Talos Vulnerability Report

SUMMARY

Multiple OS command injection vulnerabilities exist in the adm.cgi sch_reboot() functionality of Wavlink AC3000 M33A8.V5030.210505. A specially crafted HTTP request can lead to a arbitrary code execution. An attacker can make an authenticated HTTP request to trigger these vulnerabilities.

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 adm.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 only focus on the following:

00401a60                          else if (strcmp(webget_page, "sch_reboot") == 0)
00401b5c                              sch_reboot(contlen_buf)

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

004133fc  int32_t sch_reboot(int32_t arg1)

0041342c      char var_90
0041342c      memset(&var_90, 0, 0x80)
00413454      var_90 = 0x30
00413468      int32_t $v0_1 = strdup(web_get("restart_hour", arg1, 0)) // [1]
004134a0      int32_t $v0_3 = strdup(web_get("restart_min", arg1, 0))  // [2]
004134d8      int32_t $v0_5 = strdup(web_get("restart_week", arg1, 0)) // [3]
004134f8      if (sx.d(*$v0_1) == 0 || (sx.d(*$v0_1) != 0 && sx.d(*$v0_3) == 0))
00413514          nvram_bufset(0, "SCH_Reboot", 0x41628c)
004134f8      if (sx.d(*$v0_1) != 0 && sx.d(*$v0_3) != 0)
004135e0          snprintf(&var_90, 0x80, "%s %s * * %s /sbin/sch_reboot.sh reboot", $v0_3, $v0_1, $v0_5, 0x439d20) // [4]
004135fc          nvram_bufset(0, "SCH_Reboot", &var_90)  //[5]
00413624          if (access("/tmp/web_log", 0) == 0)
00413638              int32_t $v0_8 = fopen("/dev/console", &data_415758)
00413644              if ($v0_8 != 0)
00413678                  fprintf($v0_8, "%s:%s:%d:SCH_Reboot = %s \n\n", "adm.c", "sch_reboot", 0x10ae, &var_90)
00413690                  fclose($v0_8)
0041352c      nvram_commit(0)
00413544      do_system("killall schedule.sh")
0041355c      sleep(1)
00413574      do_system("schedule.sh init") // [6]
0041358c      sleep(1)
004135c0      return free_all(2, $v0_1, $v0_3)

Our provided restart_hour [1] ,restart_min [2], and restart_week [3] POST parameters are all combined into a buffer [4], and then written to the SCH_Reboot nvram item at [5]. This buffer resembles a crontab item and as we will soon see within further scripts, this line will indeed be added to a crontab and run. To see this we must look at the system call to schedule.sh init at [6]:

// [...]
echo "0 12 * * * echo 3 > /proc/sys/vm/drop_caches" >> /var/spool/cron/crontabs/"$user"
echo "0 23 * * * echo 3 > /proc/sys/vm/drop_caches" >> /var/spool/cron/crontabs/"$user"
echo "0 23 * * * killall lighttpd" >> /var/spool/cron/crontabs/"$user"
echo "1 23 * * * lighttpd -f /etc_ro/lighttpd/lighttpd.conf -m /etc_ro/lighttpd/lib" >> /var/spool/cron/crontabs/"$user"
echo  "*/2  * * * * monitor_process.sh" >> /var/spool/cron/crontabs/"$user"
echo "0 5 * * * echo 0 > /tmp/url_filter_lib_state" >> /var/spool/cron/crontabs/"$user"
if [ N`nvram_get 2860 MeshMode` == "N1" ]
then
    echo  "*/1  * * * * generate_arp.sh" >> /var/spool/cron/crontabs/"$user"
fi
#           echo "0 3 * * * init_system restart" >> /var/spool/cron/crontabs/"$user"
crond

#check current time
while true
do
    ntp_year=`date "+%Y"`
    [ $ntp_year -gt 2000 ] && break
    sleep 20
done
killall crond
sleep 1

Inside of this script we can see a crontab being created for the adm2860 user and eventually written to /var/spool/cron/crontabs/adm2860. The script then waits until the ntp service is running and there is a correct date in place. Assuming so, it continues on with the following:

// [...]
echo "excute shc_reboot.sh"
sch_reboot.sh init
// [...]

Continuing into the /sbin/sch_reboot.sh script:

#!/bin/sh

# schedule reboot
user=`nvram_get 2860 Login`
SCH_Reboot=`nvram_get 2860 SCH_Reboot`

echo "$1"
if [ "$1" = "init" ]; then
        if [ "$SCH_Reboot" != "" ]; then
            echo "$SCH_Reboot" >> /var/spool/cron/crontabs/"$user"
        fi
fi

if [ "$1" = "reboot" ]; then
    reboot
fi

We clearly see our SCH_Reboot nvram item get read in and written into the adm2860 crontab. Thus, as long as our original restart_hour [1] ,restart_min [2], or restart_week [3] variables are formatted correctly, we can inject crontab configuration into the crontab and quickly establish code execution.

CVE-2024-39781 - restart_hour injection

004133fc  int32_t sch_reboot(int32_t arg1)

0041342c      char var_90
0041342c      memset(&var_90, 0, 0x80)
00413454      var_90 = 0x30
00413468      int32_t $v0_1 = strdup(web_get("restart_hour", arg1, 0)) 

// [...]
004134f8      if (sx.d(*$v0_1) != 0 && sx.d(*$v0_3) != 0)
004135e0          snprintf(&var_90, 0x80, "%s %s * * %s /sbin/sch_reboot.sh reboot", $v0_3, $v0_1, $v0_5, 0x439d20) 

CVE-2024-39782 - restart_min injection

004133fc int32_t sch_reboot(int32_t arg1)

0041342c      char var_90
0041342c      memset(&var_90, 0, 0x80)
00413454      var_90 = 0x30
// [...]
004134a0      int32_t $v0_3 = strdup(web_get("restart_min", arg1, 0))  
// [...]
004134f8      if (sx.d(*$v0_1) != 0 && sx.d(*$v0_3) != 0)
004135e0          snprintf(&var_90, 0x80, "%s %s * * %s /sbin/sch_reboot.sh reboot", $v0_3, $v0_1, $v0_5, 0x439d20) 

CVE-2024-39783 - restart_week injection

0041342c      char var_90
0041342c      memset(&var_90, 0, 0x80)
00413454      var_90 = 0x30
// [...]
004134d8      int32_t $v0_5 = strdup(web_get("restart_week", arg1, 0)) // [3]
// [...] 
004134f8      if (sx.d(*$v0_1) != 0 && sx.d(*$v0_3) != 0)
004135e0          snprintf(&var_90, 0x80, "%s %s * * %s /sbin/sch_reboot.sh reboot", $v0_3, $v0_1, $v0_5, 0x439d20) // [4]

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