CERT/CC disclosed CVE-2026-11405, an undocumented authentication backdoor affecting multiple Tenda router firmware versions that can let attackers bypass normal login checks and gain full administrative access to the web management interface. The flaw is located in the /bin/httpd binary's login() function, where failed authentication can fall through to an alternate path that compares the supplied password against a configuration value using plaintext strcmp() logic; the associated rzadmin username is not properly validated, so any username may succeed if paired with the backdoor password.
A successful exploit could allow remote attackers to change network settings, disable security protections, redirect traffic, install malicious firmware, and maintain persistence for man-in-the-middle activity or lateral movement. CERT/CC said the issue was reported by an anonymous researcher, published as Vulnerability Note VU#213560, and remained unpatched at disclosure time after unsuccessful vendor coordination attempts, prompting guidance to disable remote web management, change the default LAN IP address, monitor for firmware updates, and consider replacing affected devices if no fix becomes available.

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On 2026-07-06, CERT/CC published Vulnerability Note VU#213560 disclosing CVE-2026-11405, an undocumented authentication backdoor in multiple Tenda router firmware versions that can grant full administrative access. The disclosure said no official patch was available at the time and recommended mitigations such as disabling remote web management.
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