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CVE-2026-51721 – Unauthenticated Access Control Bypass – TOTOLINK T6 4.1.5cu.748_B20211015

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Summary

CVE-2026-51721 is an incorrect access control vulnerability in the setPairCfg function of the TOTOLINK T6 web management interface, firmware version 4.1.5cu.748_B20211015. It allows an unauthenticated remote attacker to alter the device’s mesh pairing state, and has been assigned a CVSS v3.1 base score of 9.1 (Critical).

Technical details

  • Root cause: the setPairCfg function does not enforce authentication or authorization checks before processing requests (CWE-284, Improper Access Control).
  • Trigger condition: an attacker sends a crafted HTTP POST request to the /cgi-bin/cstecgi.cgi endpoint invoking setPairCfg.
  • Attack vector: network-based, no authentication or user interaction required, low attack complexity.
  • Impact: unauthenticated modification of the device’s mesh pairing configuration/state, with high confidentiality and integrity impact and no 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: no official patched firmware version has been identified for this issue at time of writing; check TOTOLINK’s support/download portal for updated firmware for the T6 model and apply it as soon as it becomes available.
  • If no patch is available: restrict access to the device’s web management interface (/cgi-bin/cstecgi.cgi) to trusted internal networks only, disable remote/WAN-facing management, and place the device behind a firewall or VPN so it is not directly reachable from the internet.

References

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