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CVE-2026-51733 – Unauthenticated Configuration Tampering – TOTOLINK T6 4.1.5cu.748_B20211015

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Summary

CVE-2026-51733 is an incorrect access control vulnerability in the FirmwareUpgrade function of the TOTOLINK T6 wireless router, firmware 4.1.5cu.748_B20211015. It allows a remote, unauthenticated attacker to send a crafted HTTP POST request to the device’s management CGI interface and remove Wi-Fi schedule entries without any credentials. The flaw carries a CVSS v3.1 base score of 9.8 (Critical).

Technical details

  • Root cause: the FirmwareUpgrade handler within /cgi-bin/cstecgi.cgi fails to enforce authentication/authorization checks before processing requests that modify device configuration.
  • Trigger condition: an attacker sends a specially crafted POST request to /cgi-bin/cstecgi.cgi targeting the vulnerable function.
  • Attack vector: network-based, no user interaction and no privileges required.
  • Impact: unauthorized removal of Wi-Fi schedule entries, indicating broader improper access control on the management interface; CVSS impact metrics rate confidentiality, integrity, and availability impact as High.
  • This CVE is one of several similarly-structured incorrect access control findings disclosed for the same TOTOLINK T6 firmware build and CGI endpoint.

Affected software

  • TOTOLINK T6, firmware version 4.1.5cu.748_B20211015

Severity

  • CVSS v3.1 Base Score: 9.8 (Critical)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Mitigation and recommended actions

  • Immediate: No official TOTOLINK patch has been confirmed for this specific firmware build at time of writing; check the TOTOLINK support/download portal for an updated firmware release for the T6 model and apply it as soon as it becomes available.
  • If no patch: Restrict network access to the router’s management interface (/cgi-bin/cstecgi.cgi) so it is not reachable from the public internet; disable remote/WAN administration; place the device behind a firewall or VPN limiting access to trusted management networks; monitor for unexpected configuration changes such as removed Wi-Fi schedules.

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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1

Map your entire attack surface (continously)

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2

Monitor for new CVEs

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3

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Not all CVEs matter. IONIX filters vulnerabilities by asking attacker-centric questions: Can it be reached from the internet? Does it require authentication? Is it being exploited in the wild? This dramatically reduces noise and focuses teams on threats that can actually be weaponized.

4

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5

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6

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Results are routed through integrations with ticketing, SOAR, and SIEM tools. Issues are written in plain language, bundled into remediation clusters, and prioritized based on asset criticality, exploitability, and blast radius. This shortens mean time to remediation (MTTR) and empowers teams to act with confidence.

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