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CVE-2026-51687 – Unauthenticated Guest Wi-Fi Configuration Tampering – TOTOLINK T6 (Firmware 4.1.5cu

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Summary

CVE-2026-51687 is an improper access control vulnerability (CWE-284) in TOTOLINK T6 router firmware 4.1.5cu.748_B20211015. The setWiFiEasyGuestCf function in the router’s /cgi-bin/cstecgi.cgi endpoint fails to enforce authentication, allowing unauthenticated network attackers to create or weaken the device’s guest wireless network configuration. The flaw carries a Critical CVSS v3.1 base score of 9.1.

Technical details

  • Root cause: the setWiFiEasyGuestCf handler in /cgi-bin/cstecgi.cgi does not verify that the requester is authenticated before processing guest Wi-Fi configuration changes.
  • Trigger condition: an attacker sends a crafted HTTP POST request to /cgi-bin/cstecgi.cgi invoking the setWiFiEasyGuestCf action.
  • Attack vector: Network — no authentication or user interaction is required, and the endpoint is reachable by anyone able to send requests to the device’s management interface.
  • Impact: attackers can create a new guest wireless network or weaken/remove security settings on an existing guest network, exposing the local network to unauthorized wireless access. Confidentiality and integrity impacts are rated High; availability impact is None.

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 fixed firmware version has been published by TOTOLINK for this issue at the time of writing. Check the TOTOLINK support/download portal regularly for a firmware update addressing this CVE and apply it as soon as it is released.
  • If no patch is available: Restrict access to the router’s web management interface (/cgi-bin/cstecgi.cgi) to trusted internal networks only, and disable remote/WAN-side administration. Place management interfaces behind a VPN or firewall rule limiting access to known administrator IP addresses. Monitor for unexpected changes to guest wireless network configuration.

How IONIX identifies potentially affected assets

IONIX matches the following signals against data already collected when it crawled the asset; identifying the technology sends no request beyond that crawl.

  • Raw response body: /cgi-bin/cstecgi.cgi
  • Page title: TOTOLINK

References

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Map your entire attack surface (continously)

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