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CVE-2026-51734 – Unauthenticated Access Control Bypass – TOTOLINK T6 4.1.5cu.748_B20211015

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Summary

CVE-2026-51734 is an incorrect access control vulnerability (CWE-284) in the informSlaveUpdate function of the TOTOLINK T6 router, firmware version 4.1.5cu.748_B20211015. The flaw allows an unauthenticated remote attacker to trigger mesh slave update coordination logic on the device by sending a crafted POST request to the device’s web management CGI endpoint. The issue is rated CRITICAL with a CVSS v3.1 base score of 9.8.

Technical details

  • Root cause: The informSlaveUpdate function, exposed via /cgi-bin/cstecgi.cgi, does not enforce authentication or authorization checks before processing requests.
  • Trigger conditions: An attacker sends a specially crafted HTTP POST request to /cgi-bin/cstecgi.cgi targeting the informSlaveUpdate function.
  • Attack vector: Network-based; the affected CGI endpoint is reachable over the device’s web management interface without any credentials.
  • Impact: Unauthenticated attackers can invoke mesh slave update coordination functionality on the router, affecting confidentiality, integrity, and availability of the device.

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 vendor-supplied patched firmware version has been identified in public sources at the time of this writing. Check TOTOLINK’s official download page for the T6 product line for an updated firmware release addressing this issue and apply it as soon as it is available.
  • If no patch is available: Restrict access to the device’s web management interface to trusted internal networks only; disable remote/WAN management; place the device behind a firewall or VPN so that /cgi-bin/cstecgi.cgi is not reachable from the public internet; monitor for unexpected POST requests to this endpoint.

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, N600R (Firmware version V, TOTOLINK

References

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How IONIX’s External Exposure Management Platform Detects and Validates
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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

Identify Potential External Exposures

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

Create Safe, Scalable Exploit Validations

IONIX transforms real-world PoCs into safe, non-intrusive test payloads that can be run in production environments without disruption. These simulations are precisely targeted to the systems that are vulnerable, ensuring rapid validation without unnecessary load.

5

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By combining context about software stack, versioning, exposure status, and reachability, IONIX ensures that only the right payloads are executed against the right assets, maximizing efficiency and minimizing risk.

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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