Talos Vulnerability Report

SUMMARY

A buffer overflow vulnerability exists in the internet.cgi set_add_routing() functionality of Wavlink AC3000 M33A8.V5030.210505. A specially crafted HTTP request can lead to stack-based buffer overflow. 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-120 - Buffer Copy without Checking Size of Input (‘Classic Buffer Overflow’)

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 internet.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:

00401a18              else if (strcmp(page_get, "addrouting") == 0)
00401ae4                  set_add_routing(malloc_contlen)

If we provide page=addrouting, we enter the set_wzdrepeater function and our provided POST data is further parsed therein:

00402f78  int32_t set_add_routing(int32_t arg1)

00402fc0      char buff_0x100_1[0x100]
00402fc0      memset(&buff_0x100_1, 0, 0x100)
00402fdc      char buff_0x100_2[0x100]
00402fdc      memset(&buff_0x100_2, 0, 0x100)
00402ff4      web_debug_header()
00403028      int32_t dest_1 = strdup(web_get("dest", arg1, 1))   // [1]
// [...]
004031ac      if (sx.d(*dest) != 0)
00403228          void* cmd_buff = &buff_0x100_1[strlen(&buff_0x100_1)]
00403238          *(cmd_buff + 3) = 'ut'
00403248          *(cmd_buff - 1) = 'ro'
0040324c          *(cmd_buff + 7) = 'ad'
00403254          *(cmd_buff + 3) = 'e '
00403258          *(cmd_buff + 9) = ' '
00403264          *(cmd_buff + 8) = 'd'
00403268          *(cmd_buff + 0xa) = 0
00403284          char* $a0_10 = &buff_0x100_1
00403280          if (strcmp(hostnet, "net") == 0)
004035a4              __builtin_strncpy(dest: &buff_0x100_1[strlen($a0_10)], src: "-net ", n: 6)
00403280          else
004032b8              __builtin_strncpy(dest: &buff_0x100_1[strlen($a0_10)], src: "-host ", n: 7)
004032d0          strcat(&buff_0x100_1, dest)  // [2]

Among the different POST parameters that this function can read in, we see most importantly that the dest field is read in to the heap without length checking at [1], and then read into the stack with strcat at [2]. Since our input dest field can easily reach 0x528 bytes (the stack offset of the buff_0x100_1 buffer), we can overflow and overwrite the return address of the function, resulting in arbitrary code execution.

Crash Information

Thread 2.1 "internet.cgi" hit Breakpoint 3, 0x00402f9c in set_add_routing ()
(gdb) b *0x4032d0
Breakpoint 4 at 0x4032d0
(gdb) c
Continuing.

Thread 2.1 "internet.cgi" hit Breakpoint 4, 0x004032d0 in set_add_routing ()
(gdb) x/1s $a0
0x736f682d:     <error: Cannot access memory at address 0x736f682d>
(gdb) x/1s $a1
0x55f550:       'A' <repeats 200 times>...
(gdb) c
Continuing.
[Detaching after fork from child process 31553]

Thread 2.1 "internet.cgi" received signal SIGSEGV, Segmentation fault.
0x41414141 in ?? ()
(gdb) info reg
          zero       at       v0       v1       a0       a1       a2       a3
 R0   00000000 00000000 7fd903ec 00005288 00000000 0055f550 0055fa80 0055fa90
            t0       t1       t2       t3       t4       t5       t6       t7
 R8   77cfd2b4 77cfc6e4 00000000 ffffffff 77e64000 f0000000 00000001 004031dc
            s0       s1       s2       s3       s4       s5       s6       s7
 R16  41414141 41414141 41414141 41414141 41414141 41414141 41414141 41414141
            t8       t9       k0       k1       gp       sp       s8       ra
 R24  0000004e 77d01288 00000000 00000000 77e82010 7fd90a28 41414141 41414141
        status       lo       hi badvaddr    cause       pc
      0100fc13 00111044 00000030 41414140 50800008 41414141
          fcsr      fir      hi1      lo1      hi2      lo2      hi3      lo3
      00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
        dspctl  restart
      00000000 00000000

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