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 POST request to /cgi-bin/cstecgi.cgi, targeting the setLoginPasswordCfg function.
3. The POST request includes the admpass argument containing a malicious payload designed for OS command injection.
4. The setLoginPasswordCfg function processes the admpass argument without proper sanitization.
5. The injected OS command is executed by the underlying operating system with the privileges of the web server.
6. The attacker gains arbitrary code execution on the router.
7. The attacker pivots to other internal systems.

Impact

Successful exploitation of CVE-2026-7155 allows a remote attacker to execute arbitrary commands on the affected Totolink A8000RU device. This can lead to complete compromise of the router, including modification of settings, interception of network traffic, or the use of the router as a botnet node. Given the prevalence of these devices in home and small business networks, a large number of devices are potentially vulnerable. The high CVSS score of 9.8 reflects the severity and ease of exploitation.

Recommendation

• Deploy the Sigma rule Detect Totolink A8000RU Command Injection Attempt to detect exploitation attempts against this vulnerability by monitoring web server logs.
• Apply available patches or firmware updates provided by Totolink for A8000RU 7.1cu.643_b20200521 to remediate CVE-2026-7155, if available.
• Monitor network traffic for suspicious outbound connections originating from Totolink A8000RU devices, potentially indicating successful exploitation.