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CVE-2026-79911 – Unauthenticated RCE via Stack Buffer Overflow – TOTOLINK N600R 4.3.0cu.7647_B202101

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Summary

CVE-2026-79911 is a stack-based buffer overflow vulnerability in the CGI handler of TOTOLINK N600R routers, specifically in the setSystemConfig function of /cgi-bin/cstecgi.cgi. The flaw is triggered through improper handling of the Hostname argument and can be exploited remotely without authentication to achieve memory corruption and potentially arbitrary code execution. The vulnerability carries a maximum CVSS score of 10.0 (Critical).

Technical details

  • Root cause: The setSystemConfig function in /cgi-bin/cstecgi.cgi fails to properly validate or bound-check the length of the Hostname parameter before copying it into a fixed-size stack buffer, resulting in a stack-based buffer overflow (CWE-121).
  • Trigger condition: An attacker sends a crafted HTTP request to the device’s web management CGI endpoint, supplying an oversized value for the Hostname argument to setSystemConfig.
  • Attack vector: Network-based; no authentication or user interaction is required to exploit the endpoint.
  • Impact: Successful exploitation can corrupt process memory on the stack, potentially leading to denial of service or remote code execution on the affected device, with full impact to confidentiality, integrity, and availability.

Affected software

  • TOTOLINK N600R — firmware version 4.3.0cu.7647_B20210106

Severity

  • CVSS v3.1 Base Score: 10.0 (Critical)
  • Vector: AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

Mitigation and recommended actions

  • Immediate: No vendor-supplied patched firmware version has been confirmed in public disclosure records as of this writing. Check TOTOLINK’s official support channels for a firmware update addressing this issue for the N600R and apply it as soon as it becomes available.
  • If no patch is available:
    • Restrict access to the device’s web management interface (/cgi-bin/cstecgi.cgi) to trusted internal networks only; do not expose it to the public internet.
    • Place the device behind a firewall or VPN, and disable remote/WAN-side administration if not strictly required.
    • Monitor for anomalous requests to setSystemConfig or unusually long Hostname values in web management traffic.
    • Consider replacing or isolating end-of-life TOTOLINK devices that no longer receive vendor security updates.

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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