Dinkleberry 🫐

Are you one of the 92,000+ people¹ stuck with a D-Link NAS vulnerable to CVE-2024-3272, and no patch in sight?

This tool uses the exploit itself to patch a vulnerable device.

¹: See original disclosure in refs

What it does

Dinkleberry will execute a command to swap out the vulnerable nas_sharing.cgi file with a patched version - overwriting the system() call with NOPs.

The /usr/local/modules folder (where the file lives) is read-only, so instead a copy is created in /usr/local/config, and the symlink in /var/www/cgi-bin is updated to point to the safe(r) version.

I have chosen to only NOP the system call so that the command still responds as usual, just without actually executing anything.

Note

The filesystem is re-loaded from flash on boot. Applying this patch will only work until you reboot the device. If you want a more permanent fix, you'll have to re-flash the firmware.

I leave this as an exercise for the reader ;)

Usage

aliask:~/git/dinkleberry$ python3 ./src/main.py -h                                                                                                                   10:01:02
usage: dinkleberry [-h] [--telnet] [--kill-telnet] [--test] [--verbose] target

positional arguments:
  target         Target NAS to patch

options:
  -h, --help     show this help message and exit
  --telnet       Start telnet server
  --kill-telnet  Stop telnet server
  --test         Test if device is vulnerable
  --verbose, -v  Set this to print debug messages

If no optional flags are applied, the script performs the patching.

Telnet

If you just want to poke around on the device, use the --telnet command, which starts a telnet session on port 23.

This is hilariously insecure, but your device is already hilariously insecure so may as well take the convenient shell.

Disclaimer

Caution

Use this tool at your own peril. It's modifying the actual device software.

I am not responsible for:

• Your device stopping working
• Losing data stored on the NAS
• Starting a fire
• The TA who was happily exploiting this your device being upset

Final Words

During analysis of the nas_sharing.cgi and libsmbif.so binaries, it quickly became clear that the software on this device is extremely vulnerable. Unmaintainable-rewrite-from-scratch vulnerable.

There are like 80 calls to system() in nas_sharing.cgi alone - many of these have a pathway for user input. I haven't bothered analysing them all to look for more holes to patch, but here's one S-tier example:

/*  Why use system() instead of libc fopen/fwrite?
    What if you want to write a long string or your filename is long?
    Painfully obvious command injection playground 🤦 */
void append_to_file(const char* string, const char* file) {
  char s_cmd[1024];
  sprintf(s_cmd, "echo %s >> %s", string, file);
  system(s_cmd);
  return;
}

Besides all these insane system calls, there are more buffer overflows than you can poke a stick at - and I can poke a lot of sticks.

This CVE is on CISA's KEV list - If you have one of these things on the internet, take it offline. Like now.

Maybe even take D-Link's advice and replace the EOL device. But I wouldn't buy a D-Link product that's for sure.

References

• Original disclosure: https://github.com/netsecfish/dlink
• NVD page: https://nvd.nist.gov/vuln/detail/CVE-2024-3272