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CVE-2026-51677 – Unauthenticated UPnP Configuration Tampering – TOTOLINK T6 (Firmware 4.1.5cu.748_B2

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Summary

CVE-2026-51677 is an incorrect access control vulnerability (CWE-284) in the setUPnPCfg function of the TOTOLINK T6 router web management interface, firmware version 4.1.5cu.748_B20211015. The flaw allows an unauthenticated, remote attacker to change the device’s UPnP service state by sending a crafted POST request to /cgi-bin/cstecgi.cgi. It is rated CRITICAL with a CVSS v3.1 base score of 9.1.

Technical details

  • Root cause: the setUPnPCfg handler exposed via /cgi-bin/cstecgi.cgi does not enforce authentication before processing UPnP configuration requests.
  • Trigger condition: an attacker sends a specially crafted HTTP POST request targeting the setUPnPCfg action on the CGI endpoint.
  • Attack vector: network-based, requiring no privileges and no user interaction.
  • Impact: unauthorized attackers can enable or disable the router’s UPnP service state, altering device configuration without credentials; the disclosed impact is limited to confidentiality and integrity of the affected configuration setting, with no availability impact reported.

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

  • No fixed firmware version has been confirmed in vendor or public sources at the time of writing; check TOTOLINK’s official download portal for updates to the T6 line before deploying any patch.
  • If no patch is available: restrict management interface access to trusted internal networks only, disable remote/WAN administration, and do not expose /cgi-bin/cstecgi.cgi or the device’s web management port to the internet.
  • Disable UPnP on the device if it is not required, to remove the affected functionality from the attack surface.
  • Monitor for unexpected changes to UPnP service state as an indicator of exploitation attempts.

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 HTTP response body: /cgi-bin/cstecgi.cgi, N600R (Firmware version V...), TOTOLINK

References

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1

Map your entire attack surface (continously)

IONIX uses multi-factor discovery methods, including DNS analysis, certificate mapping, metadata inspection, and more, to automatically map every internet-facing asset across your environment. This includes cloud instances, third-party platforms, shadow IT, and even forgotten infrastructure that traditional tools miss.

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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