CVE-2026-51626: TOTOLINK T6 Authentication Bypass Vulnerability

CVE-2026-51626 Overview

CVE-2026-51626 is an incorrect access control vulnerability [CWE-284] in the getWiFiWpsCfg function of the TOTOLINK T6 router running firmware version 4.1.5cu.748_B20211015. Unauthenticated attackers can retrieve the Wi-Fi Protected Setup (WPS) configuration, including the current PIN, by sending a crafted POST request to the /cgi-bin/cstecgi.cgi endpoint. Disclosure of the WPS PIN enables adversaries to associate with the wireless network and pivot into internal segments. The flaw requires no authentication and no user interaction, and it is exploitable over the network.

Critical Impact

An unauthenticated attacker with network reachability to the device web interface can obtain the WPS PIN and gain wireless access to the protected network.

Affected Products

• TOTOLINK T6 router firmware 4.1.5cu.748_B20211015
• The vulnerable getWiFiWpsCfg handler in /cgi-bin/cstecgi.cgi
• Deployments exposing the device management HTTP interface to untrusted networks

Discovery Timeline

• 2026-08-28 - CVE-2026-51626 published to the National Vulnerability Database
• 2026-09-01 - Last updated in NVD database

Technical Details for CVE-2026-51626

Vulnerability Analysis

The TOTOLINK T6 web management interface exposes a Common Gateway Interface (CGI) binary at /cgi-bin/cstecgi.cgi that dispatches configuration requests based on a function selector in the POST body. The getWiFiWpsCfg handler returns the current WPS configuration, including the active PIN, but does not verify that the requester holds an authenticated administrative session. Any client that can reach the HTTP endpoint can invoke the handler and receive sensitive configuration data in the response. The WPS PIN is a short numeric secret used to authorize wireless association. Once exposed, it allows an attacker to join the wireless LAN without knowing the Wi-Fi passphrase. See the coordination write-up at DarkBoulder CVE-Vendor-Coordination and ShengWu00 CVE-Vendor-Coordination for reference details.

Root Cause

The root cause is a missing authorization check on a sensitive configuration handler. The CGI dispatcher routes requests to getWiFiWpsCfg without validating a session cookie, token, or source restriction. This is a classic broken access control weakness [CWE-284] where the function trusts the request context implicitly.

Attack Vector

An attacker crafts a POST request to /cgi-bin/cstecgi.cgi targeting the getWiFiWpsCfg handler. No credentials are attached. The device returns a JSON payload containing WPS state and the current PIN. The attacker then uses the PIN with a standard WPS client to associate with the wireless network. Exploitation is trivial to script and can be executed remotely if the management interface is reachable, or from the LAN or adjacent wireless segment in a default deployment.

No verified proof-of-concept code is published in the enriched data. Refer to the linked vendor coordination repositories for further technical detail.

Detection Methods for CVE-2026-51626

Indicators of Compromise

• HTTP POST requests to /cgi-bin/cstecgi.cgi referencing the getWiFiWpsCfg function from unexpected source addresses
• Outbound responses from the router containing WPS PIN fields to non-administrative hosts
• Unrecognized wireless client associations shortly after suspicious HTTP activity against the router management interface

Detection Strategies

• Inspect router access logs and any upstream network sensor for POST requests to cstecgi.cgi that reference WPS configuration retrieval
• Correlate HTTP requests to the router management endpoint with subsequent new wireless client MAC addresses on the same network
• Deploy network monitoring rules that flag unauthenticated queries against embedded CGI endpoints on SOHO gateway devices

Monitoring Recommendations

• Restrict and log all access to the router HTTP management interface, and alert on requests originating outside the management VLAN
• Track WPS association events on the wireless controller or access point and treat unexpected WPS-based joins as high priority
• Baseline expected administrative source addresses and alert on deviations targeting /cgi-bin/cstecgi.cgi

How to Mitigate CVE-2026-51626

Immediate Actions Required

• Disable WPS on the TOTOLINK T6 device until a fixed firmware is available
• Block access to the router HTTP management interface from the WAN and from untrusted internal segments
• Rotate the Wi-Fi passphrase and any pre-shared keys after confirming no unauthorized associations have occurred
• Inventory all TOTOLINK T6 units running firmware 4.1.5cu.748_B20211015 and prioritize them for remediation

Patch Information

No vendor patch is referenced in the enriched CVE data at the time of publication. Monitor the TOTOLINK Download Page and the TOTOLINK Official Website for firmware updates addressing the getWiFiWpsCfg access control flaw. Apply the fixed firmware to all affected T6 units once released.

Workarounds

• Turn off WPS in the router administrative UI to prevent PIN-based wireless association even if the PIN is disclosed
• Place the router management interface behind an access control list that only permits designated administrative hosts
• Segment the wireless network from sensitive internal assets so that a compromised Wi-Fi association does not grant lateral access

# Example firewall restriction limiting management access to a trusted host
iptables -A INPUT -p tcp --dport 80 -s 192.0.2.10 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP