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CVE-2026-51722 – Unauthenticated Wi-Fi Repeater Reconfiguration / MITM – TOTOLINK T6 4.1.5cu.748_B20

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Summary

CVE-2026-51722 is an incorrect access control vulnerability in the setWiFiRepeaterCfg function of the TOTOLINK T6 router, firmware 4.1.5cu.748_B20211015. It allows an unauthenticated remote attacker to send a crafted request to the device’s web management CGI interface and repoint the router to an attacker-controlled upstream Wi-Fi network. The flaw carries a CVSS v3.1 base score of 9.1 (Critical).

Technical details

  • Root cause: The setWiFiRepeaterCfg function, exposed via /cgi-bin/cstecgi.cgi, fails to enforce proper authentication/authorization checks before processing configuration requests (CWE-284: Improper Access Control).
  • Trigger condition: An attacker sends a crafted HTTP POST request to /cgi-bin/cstecgi.cgi invoking the setWiFiRepeaterCfg action, without needing valid session credentials.
  • Attack vector: Network-based; no privileges and no user interaction required.
  • Impact: The attacker can alter the device’s Wi-Fi repeater/upstream configuration, redirecting the router’s traffic through an attacker-controlled Wi-Fi network — enabling traffic interception, man-in-the-middle positioning, or further network compromise. The vulnerability affects confidentiality and integrity (no direct availability impact).

Affected software

  • TOTOLINK T6, firmware version 4.1.5cu.748_B20211015

Severity

  • CVSS v3.1 Base Score: 9.1 (Critical)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Mitigation and recommended actions

  • Immediate: Check TOTOLINK’s official firmware download page for an updated release for the T6 model that addresses this issue, and apply it as soon as it is available.
  • If no patch is available: Restrict access to the router’s web management interface (/cgi-bin/cstecgi.cgi) so it is not reachable from the public internet; disable remote/WAN administration; place management access behind a VPN or firewall ACL limited to trusted internal hosts; monitor for unexpected Wi-Fi repeater/upstream configuration changes.

References

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