CVE-2026-51631 Overview
CVE-2026-51631 is an incorrect access control vulnerability in the getStaticDhcpRules function of TOTOLINK T6 firmware version 4.1.5cu.748_B20211015. The flaw allows unauthenticated attackers on an adjacent network to obtain Wi-Fi Protected Setup (WPS) runtime status by sending a crafted HTTP POST request to /cgi-bin/cstecgi.cgi. The weakness is categorized under [CWE-284] Improper Access Control.
Critical Impact
Unauthenticated attackers within the adjacent network can enumerate WPS runtime status without credentials, exposing device configuration data useful for follow-on attacks.
Affected Products
- TOTOLINK T6 router, firmware version 4.1.5cu.748_B20211015
- Web management CGI endpoint /cgi-bin/cstecgi.cgi
- getStaticDhcpRules handler function
Discovery Timeline
- 2026-08-28 - CVE-2026-51631 published to NVD
- 2026-09-01 - Last updated in NVD database
Technical Details for CVE-2026-51631
Vulnerability Analysis
The TOTOLINK T6 router exposes a Common Gateway Interface (CGI) endpoint at /cgi-bin/cstecgi.cgi that multiplexes administrative operations based on a request parameter. One dispatched handler, getStaticDhcpRules, returns configuration data including WPS runtime status.
The handler does not verify that the requester holds an authenticated administrative session before returning the data. Any device that can reach the router's management interface can query the endpoint and receive the response. Because the attack vector is Adjacent Network (AV:A), an attacker must be positioned on the same logical or physical network segment as the router.
The disclosure impacts confidentiality only. Integrity and availability of the device are not affected by this specific access-control gap, though the leaked WPS state can support subsequent attacks against the Wi-Fi authentication stack.
Root Cause
The root cause is a missing authentication check inside getStaticDhcpRules. The function returns operational data without validating the session token or cookie provided by the client. This pattern reflects [CWE-284] Improper Access Control, where the resource is served to any caller that reaches the endpoint.
Attack Vector
Exploitation requires network adjacency to the vulnerable router and the ability to issue an HTTP POST request to /cgi-bin/cstecgi.cgi with a crafted body invoking getStaticDhcpRules. No credentials, no user interaction, and no elevated privileges are required. The router responds with WPS runtime status information that would normally be restricted to authenticated administrators.
Refer to the GitHub CVE Coordination Resource for the coordinated disclosure record and additional technical context.
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Stop Identity AttacksDetection Methods for CVE-2026-51631
Indicators of Compromise
- Unauthenticated HTTP POST requests to /cgi-bin/cstecgi.cgi originating from clients on the local or guest network.
- Request bodies containing the getStaticDhcpRules action or topic parameter without a preceding successful login.
- Anomalous polling patterns against the router management interface from non-administrator hosts.
Detection Strategies
- Inspect HTTP traffic destined for router management interfaces and flag requests to cstecgi.cgi that reference getStaticDhcpRules outside of authenticated administrator sessions.
- Correlate management-plane requests with authentication events; requests without a prior authenticated session should be treated as suspicious.
- Baseline expected administrative source IPs and alert on new or unmanaged hosts querying router configuration endpoints.
Monitoring Recommendations
- Forward router access logs and network flow data to a centralized analytics platform for retention and query.
- Monitor for repeated POST requests to /cgi-bin/cstecgi.cgi from IoT segments, guest Wi-Fi, or untrusted VLANs.
- Track WPS status changes and correlate them with unauthenticated queries against the management interface.
How to Mitigate CVE-2026-51631
Immediate Actions Required
- Restrict access to the router management interface to trusted administrative hosts using firewall or ACL rules.
- Segment IoT devices, guest Wi-Fi, and unmanaged clients away from the router LAN interface used for administration.
- Disable WPS on the TOTOLINK T6 until a firmware update is available to reduce downstream exposure from leaked WPS state.
- Rotate administrator credentials and Wi-Fi pre-shared keys if suspicious queries against cstecgi.cgi are observed.
Patch Information
At the time of publication, no vendor advisory or patched firmware for TOTOLINK T6 has been referenced in the NVD entry. Check the TOTOLINK Download Page and the TOTOLINK Official Website for firmware releases superseding 4.1.5cu.748_B20211015.
Workarounds
- Place the router management interface behind a management VLAN reachable only from administrator workstations.
- Block inbound traffic to /cgi-bin/cstecgi.cgi from untrusted network segments at an upstream firewall where feasible.
- Replace end-of-support consumer routers with devices that receive active vendor security maintenance if a firmware fix is not published.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
