Talos Vulnerability Report

SUMMARY

An os command injection vulnerability exists in the nas.cgi remove_dir() functionality of Wavlink AC3000 M33A8.V5030.210505. A specially crafted HTTP request can lead to arbitrary code execution. An attacker can make an authenticated HTTP request to trigger this vulnerability.

CONFIRMED VULNERABLE VERSIONS

The versions below were either tested or verified to be vulnerable by Talos or confirmed to be vulnerable by the vendor.

Wavlink AC3000 M33A8.V5030.210505

PRODUCT URLS

Wavlink AC3000 - https://www.wavlink.com/en_us/product/WL-WN533A8.html

CVSSv3 SCORE

9.1 - CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H

CWE

CWE-77 - Improper Neutralization of Special Elements used in a Command (‘Command Injection’)

DETAILS

The Wavlink AC3000 wireless router is predominately one of the most popular gigabit routers in the US, in part due to both its potential wireless and wired speed capabilities and extremely low price point (costing at the time of this writing ~$60 USD). Among the configuration options, it’s also able to act as a standalone wireless gateway, a basic network router, or a wireless repeater.

When interacting with and configuring the Wavlink AC3000 wifi router, as is typical of most wifi routers, an administrator logs in via some web portal and configures appropriate options via the HTTP interface. In the case of this particular router, and in another somewhat common execution pattern, these HTML pages can invoke .cgi binaries due to how the lighttpd server is configured. Since all of these .shtml and .cgi files are located in the web root, anyone with network access to the device doesn’t actually need to log in to the device to interact with these .cgi files, and it usually is the responsibility of the .cgi binary to check if the authentication is completed successfully. On this device, one will see a check_valid_user() function in each individual .cgi binary which will check the session cookie of the HTTP request to see if it’s coming from a validly logged in user.

Assuming that we’ve passed this check in the nas.cgi binary, we then run into a set of functions that we can call based off of what we pass for the page= parameter in our HTTP POST request. Of the available commands, we focus on the following:

00400bfc          if (contlenp1 s>= 2)
00400c08              if (contlenp1 s>= 0x200)
00400d58                  contlenp1 = 0x200
00400c1c              char inpbuf[0x200]
00400c1c              memset(&inpbuf, 0, 0x200)
00400c38              fgets(&inpbuf, contlenp1, *stdin)
00400c54              int32_t $v0_8 = web_get("page", &inpbuf, 0)
// [...]
00400cb4              else if (strcmp($v0_8, "rmdir") == 0)
00400e28                  remove_dir(&inpbuf, 0x400000)

While our input POST data is limited to 0x200 bytes, if we provide page=rmdir, we enter the remove_dir function and our provided POST data is further parsed therein.

00401530  int32_t remove_dir(int32_t arg1)

00401570      do_system("rm -rf "%s"", web_get("dir_path", arg1, 0)) // [1]
00401588      int32_t $v0_1 = getenv("HTTP_REFERER")
0040159c      if ($v0_1 == 0)
004015bc          return web_redirect("#") __tailcall
004015a8      return web_redirect($v0_1) __tailcall

Couldn’t be more straight forward, we just throw a subshell command into our dir_path HTTP POST parameter and we run an arbitrary command on the system, resulting in code execution.

TIMELINE

2024-07-25 - Initial Vendor Contact
2024-07-29 - Requesting reply from vendor
2024-07-30 - Vendor confirms receipt
2024-07-30 - Vendor Disclosure
2024-07-30 - Vendor confirms receipt
2024-09-02 - Status update request sent
2024-10-15 - Status update request. Upcoming expiration date announced.
2024-10-22 - Vendor replies product has been discontinued, but patches are being worked on
2024-11-04 - Status update request for patch release dates
2024-11-12 TALOS advisory release date announced
2025-01-14 - Public Release