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CVE-2026-51715 – Unauthenticated MAC Filter Rule Deletion – TOTOLINK T6 4.1.5cu.748_B20211015

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Summary

CVE-2026-51715 is an incorrect access control vulnerability in the delMacFilterRules function of the TOTOLINK T6 router’s web management interface (firmware 4.1.5cu.748_B20211015). It allows a remote, unauthenticated attacker to remove configured MAC filter rules by sending a crafted POST request to /cgi-bin/cstecgi.cgi. The flaw carries a CVSS v3.1 base score of 9.8 (Critical).

Technical details

  • Root cause: the delMacFilterRules handler exposed via /cgi-bin/cstecgi.cgi does not enforce session/authentication checks before processing requests that delete MAC filter rules.
  • Trigger conditions: an attacker sends a crafted HTTP POST request containing the delMacFilterRules action/topic to the device’s CGI endpoint; no valid credentials or prior session are required.
  • Attack vector: Network — the web management interface must be reachable over the network (including the internet, if exposed).
  • Impact: an unauthenticated attacker can remove MAC address filtering rules, weakening the device’s access-control posture and potentially allowing unauthorized devices onto the network. The associated CVSS vector (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H) reflects high confidentiality, integrity, and availability impact.

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 the TOTOLINK support/download site for a firmware update addressing this vulnerability for the T6 model and apply it as soon as it is available; no patched version was confirmed at the time of publication.
  • If no patch is available: Restrict access to the router’s web management interface to trusted internal networks only (disable remote/WAN administration), place the device behind a firewall or VPN, and monitor for unexpected changes to MAC filter configurations.

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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How IONIX’s External Exposure Management Platform Detects and Validates
Zero-Days to Shrink MTTR

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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