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CVE-2026-51698 – Unauthenticated Access Control Bypass (URL Filter Policy Tampering) – TOTOLINK T6 4

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Summary

CVE-2026-51698 is an incorrect access control vulnerability in the setUrlFilterRules function of TOTOLINK T6 routers running firmware 4.1.5cu.748_B20211015. The flaw allows an unauthenticated, remote attacker to modify device browsing/URL filtering policies by sending a crafted POST request to the device’s /cgi-bin/cstecgi.cgi endpoint. It carries a CRITICAL CVSS v3.1 base score of 9.1.

Technical details

  • Root cause: The setUrlFilterRules handler within /cgi-bin/cstecgi.cgi fails to enforce proper access control (CWE-284), allowing configuration-changing requests to be processed without authentication.
  • Trigger conditions: An attacker sends a specially crafted HTTP POST request to /cgi-bin/cstecgi.cgi invoking the setUrlFilterRules function.
  • Attack vector: Network-based (AV:N), low attack complexity, no privileges or user interaction required.
  • Impact: Confidentiality and integrity are both rated High — an attacker can alter the device’s URL/browsing filter rules, potentially exposing or redirecting network traffic; 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 vendor-issued patched firmware version is confirmed in the published CVE record as of this writing; check the TOTOLINK support/download portal for updated firmware for the T6 model and apply it as soon as it becomes available.
  • If no patch is available:
    • Do not expose the router’s web management interface (/cgi-bin/cstecgi.cgi) to the public internet.
    • Restrict access to the management interface to trusted internal networks only, using firewall rules or network segmentation.
    • Disable remote/WAN-side administration if enabled.
    • Monitor for unexpected changes to URL filtering/browsing policy configuration 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 response body: /cgi-bin/cstecgi.cgi, 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

Dozens of threat intel feeds using agentic technology are continuously analyzed to detect the appearance of proof-of-concept code, exploit kits, and indicators of active targeting. IONIX goes further by applying AI to proactively evaluate whether emerging vulnerabilities are likely to be exploited, even before PoCs go public.

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

Execute Exploit Validations

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

Drive Fast and Actionable Remediation

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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