Command Injection Vulnerability in /bin/protest Binary on Multiple D-Link Routers
MediumSynopsis
Command Injection in /bin/protest
AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H (7.8/7.1)
The /bin/protest binary on various D-Link router firmware images is vulnerable to command injection. This allows an authenticated attacker to execute arbitrary shell commands as root, and can easily be used to obtain a root shell on the device.
In order to exploit this vulnerability, we first need to obtain access to the /bin/cli interface over telnet. In order to access this interface on the DIR-2640, we must first:
- download the router's configuration binary
- decrypt and unpack that binary using D-Link's own mkconfig binary, which can be found on several of their firmware images
- set the telnetEnabled field in config_2g to 1
- repack and re-encrypt the config file using the same tool
- upload the modified config through the router's web interface
- connect to the router over telnet on port 23
We will then be prompted for a password. The password will be the one set as the admin password for the web UI followed by the suffix @twsz2018.
This will take us to the "router> " prompt.
The command injection vulnerability can then be triggered with the following input:
protest --fota -client_secret -w ;telnetd\${IFS}-b0.0.0.0:4444\${IFS}-l\${IFS}/bin/sh\${IFS}
This will launch a telnet shell, listening on port 4444, which may then be accessed without providing any further authentication.
Demonstration of Vulnerability on DIR-2640 Firmware Version 1.11B2
We have established that this vulnerability exists on the DIR-2640 router, running firmware version 1.11B2, as shown in the animated GIF below.
By running tests in a series of virtual environments, I have also been able to establish, with reasonable confidence, that the router models and firmware versions indicated in this advisory are affected by this command injection vulnerability.
Those images were tested the following fashion:
- First, the firmware image was unpacked (and decrypted, if necessary), and the root file system isolated.
- I then checked for a binary named protest was found on the filesystem. If no such binary was found, then the image was ignored.
- I would then ensure that the cli binary was present as well, and that the protest functionality could be triggered from the cli interface.
- Using a QEMU emulator for the appropriate architecture, I executed the cli binary inside a chroot jail, restricted to the firmware image's root filesystem, under supervision by strace, and fed the cli process a payload similar to the one shown above. The injected command, however, was set to
/VULNERABLE. - I then inspected the strace output to see if a system call beginning with
execve("/VULNERABLE"had taken place. If it had, this meant that command injection was possible on that build of protest, exposed through the cli interface.
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Risk Information
Olivia Lucca Fraser
7.8/7.1
AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H
DIR-1360 A1 firmware version 1.02B03
DIR-1360 A1 firmware version 1.03B02
DIR-1360 A1 firmware version 1.11B04
DIR-1360 firmware version 1.00B15
DIR-1360 firmware version 1.01B03
DIR-1360 firmware version 1.11B04 Beta for WPA2 2020/11/03
DIR-1760 firmware version 1.01B04
DIR-1760 firmware version 1.11B03 Beta for WPA2 2020/11/03
DIR-1960 A1 firmware version 1.02B01
DIR-1960 A1 firmware version 1.03B03
DIR-1960 A1 firmware version 1.11B03
DIR-1960 firmware version 1.11B03 Beta for WPA2 2020/11/03
DIR-2640 A1 firmware version 1.01B04
DIR-2640 A1 firmware version 1.11B02
DIR-2640 firmware version 1.11B02 Beta for WPA2 2020/11/03
DIR-2660 A1 firmware version 1.04B03
DIR-2660 A1 firmware version 1.11B04
DIR-2660 firmware version 1.00B14
DIR-2660 firmware version 1.01B03
DIR-2660 firmware version 1.02B01
DIR-2660 firmware version 1.03B04
DIR-2660 firmware version 1.11B04 Beta for WPA2 2020/11/03
DIR-3040 A1 firmware version 1.11B02
DIR-3040 A1 firmware version 1.12B01
DIR-3040 A1 firmware version 1.13B03
DIR-3040 A1 firmware version 1.20B03
DIR-3040 firmware version 1.13B03 Beta for WPA2 2020/11/03
DIR-3060 A1 firmware version 1.01B07
DIR-3060 A1 firmware version 1.02B03
DIR-3060 A1 firmware version 1.11B02 Beta for Guest zone connect issue 2020/01/19
DIR-3060 A1 firmware version 1.11B04
DIR-3060 firmware version 1.00B12
DIR-3060 firmware version 1.11B04 Beta for WPA2 2020/11/03
DIR-867 A1 firmware version 1.20B10
DIR-867 firmware version 1.10B04
DIR-867 firmware version 1.30B07
DIR-878 firmware version 1.20B05
DIR-878 firmware version 1.30B08
DIR-882 A1 firmware version 1.30B06
DIR-882 A1 firmware version 1.30B10
DIR-882 firmware version 1.20B06
Medium
router
command injection