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CVE-2026-51724 – Unauthenticated Improper Access Control – TOTOLINK T6 4.1.5cu.748_B20211015

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Summary

CVE-2026-51724 is an improper access control vulnerability (CWE-284) affecting the delSmartQosCfg function on TOTOLINK T6 routers running firmware 4.1.5cu.748_B20211015. The flaw allows an unauthenticated remote attacker to remove configured Smart QoS rules by sending a crafted POST request to the device’s CGI interface. The vulnerability carries a CVSS v3.1 base score of 9.8 (Critical).

Technical details

  • Root cause: the delSmartQosCfg function in the device’s web management CGI handler does not enforce authentication or authorization checks before processing requests that delete Smart QoS configuration entries.
  • Trigger condition: an attacker sends a specially crafted HTTP POST request to /cgi-bin/cstecgi.cgi invoking the delSmartQosCfg action.
  • Attack vector: Network — the endpoint is reachable over the network with no prior authentication, no privileges, and no user interaction required.
  • Impact: unauthorized removal of Smart QoS rules, altering the device’s traffic-shaping/QoS configuration without owner consent; the vulnerability is rated with high impact to confidentiality, integrity, and availability.

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: Check TOTOLINK’s official download page for a firmware update addressing this issue for the T6 model and apply it as soon as it is available; no fixed version is confirmed in the public record at this time.
  • If no patch is available: restrict access to the router’s web management interface (/cgi-bin/cstecgi.cgi) to trusted internal networks only, disable remote/WAN management, and place the device behind a firewall or VPN to prevent unauthenticated internet-facing access to the CGI interface.

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
Zero-Days to Shrink MTTR

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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