Totolink WA300 Buffer Overflow Vulnerability (CVE-2026-7719)

A critical buffer overflow vulnerability, identified as CVE-2026-7719, has been discovered in Totolink WA300 version 5.2cu.7112_B20190227. This vulnerability resides within the loginauth function of the /cgi-bin/cstecgi.cgi file, affecting the POST Request Handler component. The vulnerability is triggered by manipulating the http_host argument in a POST request. The exploit is publicly available, increasing the risk of widespread exploitation. This vulnerability allows for remote code execution, potentially granting attackers full control over the affected device. The affected version was released in February 2019. Defenders should prioritize patching or mitigating this vulnerability to prevent potential compromise.

Attack Chain

1. The attacker identifies a vulnerable Totolink WA300 device running firmware version 5.2cu.7112_B20190227.
2. The attacker crafts a malicious HTTP POST request targeting the /cgi-bin/cstecgi.cgi endpoint.
3. The crafted POST request includes a specially crafted http_host argument designed to overflow the buffer in the loginauth function.
4. The vulnerable loginauth function processes the http_host argument without proper bounds checking.
5. The oversized http_host argument overwrites adjacent memory regions, including the return address on the stack.
6. Upon completion of the loginauth function, the overwritten return address is used, redirecting execution to attacker-controlled code.
7. The attacker-controlled code executes with elevated privileges, allowing the attacker to execute arbitrary commands on the device.
8. The attacker gains complete control of the device, potentially using it for malicious purposes such as botnet participation, data theft, or further network penetration.

Impact

Successful exploitation of CVE-2026-7719 allows a remote attacker to execute arbitrary code on the vulnerable Totolink WA300 device. This can lead to complete device compromise, allowing the attacker to steal sensitive information, use the device as a botnet node, or pivot to other devices on the network. Given the public availability of the exploit, widespread exploitation is possible, potentially affecting a large number of home and small business networks using the vulnerable device.

Recommendation

• Deploy the Sigma rule Detect Totolink WA300 HTTP Host Buffer Overflow Attempt to identify exploitation attempts in web server logs.
• Monitor web server logs for POST requests to /cgi-bin/cstecgi.cgi with unusually long http_host headers.
• Consider deploying a web application firewall (WAF) rule to filter out malicious requests targeting CVE-2026-7719.
• Upgrade to a patched version of the firmware or replace the affected device to remediate the vulnerability.