TOTOLINK A7000R Stack-Based Buffer Overflow Vulnerability

A stack-based buffer overflow vulnerability, tracked as CVE-2026-6168, has been identified in TOTOLINK A7000R routers with firmware versions up to 9.1.0u.6115. The vulnerability resides within the setWiFiEasyGuestCfg function located in the /cgi-bin/cstecgi.cgi file. Successful exploitation allows a remote attacker to execute arbitrary code on the device. Publicly available exploit code exists, increasing the risk of widespread exploitation. Given the widespread use of TOTOLINK devices, this vulnerability poses a significant threat to home and small business networks. Exploitation is possible with low privileges, as it only requires authentication to the device’s web interface.

Attack Chain

1. Attacker authenticates to the TOTOLINK A7000R web interface. This step assumes default credentials or compromised credentials.
2. The attacker crafts a malicious HTTP POST request targeting the /cgi-bin/cstecgi.cgi endpoint.
3. The request includes the setWiFiEasyGuestCfg function call.
4. The ssid5g argument within the POST request is populated with a string exceeding the buffer’s capacity.
5. The vulnerable setWiFiEasyGuestCfg function in /cgi-bin/cstecgi.cgi processes the oversized ssid5g argument without proper bounds checking.
6. This leads to a stack-based buffer overflow, overwriting adjacent memory regions.
7. The attacker leverages the overflow to inject and execute arbitrary code on the device.
8. Successful code execution can grant the attacker full control of the router, enabling further malicious activities.

Impact

Successful exploitation of CVE-2026-6168 allows a remote attacker to execute arbitrary code on the vulnerable TOTOLINK A7000R device. This can lead to complete compromise of the router, including the ability to intercept network traffic, modify DNS settings, inject malicious scripts into websites, and use the router as a pivot point for further attacks within the network. This vulnerability affects potentially thousands of devices, particularly in home and small business environments.

Recommendation

• Apply firmware updates immediately if TOTOLINK releases a patch for CVE-2026-6168.
• Monitor web server logs for POST requests to /cgi-bin/cstecgi.cgi with unusually long ssid5g parameters, using the provided Sigma rule.
• Implement network intrusion detection systems (IDS) rules to detect attempts to exploit stack-based buffer overflows targeting TOTOLINK devices.
• Restrict access to the router’s web interface to trusted IP addresses, if possible.
• Enforce strong and unique passwords for all router accounts.