Totolink WA300 Buffer Overflow Vulnerability in UploadCustomModule

A buffer overflow vulnerability has been identified in Totolink WA300 wireless router, specifically version 5.2cu.7112_B20190227. The vulnerability resides within the UploadCustomModule function of the /cgi-bin/cstecgi.cgi file, a component of the POST Request Handler. The identified vulnerability allows a remote attacker to cause a buffer overflow through manipulation of the File argument within a crafted POST request. Public proof-of-concept exploit code is available, increasing the likelihood of exploitation. This vulnerability poses a significant risk, as successful exploitation could lead to arbitrary code execution, potentially allowing attackers to fully compromise affected devices. Defenders should prioritize detection and mitigation strategies to prevent exploitation.

Attack Chain

1. Attacker identifies a vulnerable Totolink WA300 device running firmware version 5.2cu.7112_B20190227.
2. Attacker crafts a malicious POST request targeting the /cgi-bin/cstecgi.cgi endpoint.
3. The POST request includes a File argument with a payload exceeding the buffer size allocated for the UploadCustomModule function.
4. The UploadCustomModule function processes the POST request without proper bounds checking on the File argument.
5. The oversized File argument overwrites adjacent memory regions, including potentially critical program data and control flow instructions.
6. The buffer overflow allows the attacker to inject and execute arbitrary code on the device.
7. The attacker gains remote shell access to the device with elevated privileges.
8. The attacker could then use the compromised device to pivot into the internal network or cause a denial-of-service condition.

Impact

Successful exploitation of this buffer overflow vulnerability can lead to complete compromise of the affected Totolink WA300 device. An attacker could gain unauthorized access to the device’s configuration, intercept network traffic, or use the device as a bot in a larger attack. Given the high CVSS score of 8.8, the impact is considered critical. Home and small business networks using the affected router model are at risk. The vulnerability allows for remote code execution, leading to significant potential for damage.

Recommendation

• Deploy the Sigma rule Detect Totolink WA300 UploadCustomModule Buffer Overflow Attempt to detect malicious POST requests targeting the vulnerable endpoint.
• Monitor web server logs for POST requests to /cgi-bin/cstecgi.cgi with unusually large File parameters, as indicated in the Sigma rule.
• Apply any available firmware updates from Totolink to patch CVE-2026-7717 if they become available.
• Implement network segmentation to limit the impact of a compromised router on other internal network resources.