Attack Chain

1. The attacker identifies a vulnerable Totolink A8000RU router running firmware version 7.1cu.643_b20200521.
2. The attacker sends a crafted HTTP request to the /cgi-bin/cstecgi.cgi endpoint, targeting the setIpQosRules function.
3. The HTTP request includes a malicious payload within the Comment argument designed to inject OS commands.
4. The web server processes the request and passes the Comment argument to the vulnerable setIpQosRules function without proper sanitization.
5. The injected OS commands are executed with the privileges of the web server process.
6. The attacker gains remote code execution on the router.
7. The attacker can then perform actions such as modifying router configurations, installing backdoors, or pivoting to other devices on the network.
8. The attacker achieves complete control over the compromised router.

Impact

Successful exploitation of CVE-2026-9475 results in complete compromise of the Totolink A8000RU router. An attacker can gain full control of the device, potentially leading to data theft, network disruption, or use of the router as part of a botnet. Given the ease of exploitation and the availability of public exploits, a large number of devices could be targeted, impacting both home and small business networks.

Recommendation

• Apply the vendor patch as soon as it becomes available.
• Monitor web server logs for suspicious POST requests to /cgi-bin/cstecgi.cgi with unusual characters in the Comment parameter, as detected by the Sigma rule “Detect CVE-2026-9475 Exploitation Attempt via Web Logs”.
• Implement network intrusion detection system (IDS) rules to detect and block exploitation attempts targeting CVE-2026-9475.
• Disable remote administration access to the router to limit the attack surface.
• Deploy the Sigma rule “Detect CVE-2026-9475 Command Injection via Process Creation” to identify processes spawned from the web server with injected commands.