CVE-2026-51710: TOTOLINK T6 Auth Bypass Vulnerability

CVE-2026-51710 Overview

CVE-2026-51710 is an improper access control vulnerability in the setParentalRules function of the TOTOLINK T6 router running firmware 4.1.5cu.748_B20211015. The flaw allows unauthenticated remote attackers to alter parental-control behavior by sending a crafted HTTP POST request to the /cgi-bin/cstecgi.cgi endpoint. The weakness is classified under CWE-284 (Improper Access Control) and is exploitable over the network without user interaction.

Critical Impact

Unauthenticated attackers on the same network as the router can modify parental-control policy, bypassing intended access restrictions and impacting the confidentiality and integrity of the device configuration.

Affected Products

• TOTOLINK T6 router
• Firmware version 4.1.5cu.748_B20211015
• CGI endpoint /cgi-bin/cstecgi.cgi handling the setParentalRules function

Discovery Timeline

• 2026-08-31 - CVE-2026-51710 published to the National Vulnerability Database (NVD)
• 2026-09-01 - Last updated in NVD database

Technical Details for CVE-2026-51710

Vulnerability Analysis

The TOTOLINK T6 router exposes a common gateway interface (CGI) handler at /cgi-bin/cstecgi.cgi. This handler dispatches requests to internal functions based on parameters supplied in the request body. The setParentalRules function accepts and applies parental-control policy changes without validating whether the caller is authenticated or authorized.

Because the function is reachable via unauthenticated POST requests, an attacker with network access to the router's management interface can invoke it directly. The request format follows the standard cstecgi.cgi JSON body pattern used across TOTOLINK devices, where a topicurl field selects the target function and additional fields carry the policy parameters.

Successful exploitation lets an attacker enable, disable, or rewrite parental-control rules that govern which clients can reach which destinations. This affects the integrity of enforced network policy on the device.

Root Cause

The root cause is a missing authorization check inside the setParentalRules handler. The CGI dispatcher does not require a valid session token, nor does the handler verify caller identity before mutating the configuration. This is a classic instance of CWE-284 where access-control logic is absent from a privileged administrative function.

Attack Vector

Exploitation requires only network reachability to the router's HTTP service. An attacker sends a crafted HTTP POST to /cgi-bin/cstecgi.cgi with a JSON body invoking setParentalRules and the desired policy parameters. No credentials, tokens, or user interaction are required. Attackers on the local network, on a compromised device inside the LAN, or with access to devices where the management interface is exposed to a wider network can trigger the flaw.

No verified exploit code is publicly indexed for this identifier. Technical coordination details are available in the DarkBoulder CVE coordination repository and the ShengWu00 CVE coordination repository.

Detection Methods for CVE-2026-51710

Indicators of Compromise

• Unauthenticated HTTP POST requests to /cgi-bin/cstecgi.cgi containing a topicurl value of setParentalRules.
• Unexpected changes in parental-control rules, MAC filter lists, or scheduled blocking entries on the TOTOLINK T6.
• Repeated POST requests to cstecgi.cgi from a single LAN host or external source over a short interval.

Detection Strategies

• Inspect router HTTP access logs for POST requests to /cgi-bin/cstecgi.cgi that lack a preceding authentication request from the same source.
• Baseline the router's configuration and alert on any change to parental-control policy that does not correlate with an administrator session.
• Deploy network intrusion detection signatures for POST bodies referencing setParentalRules originating from non-administrative hosts.

Monitoring Recommendations

• Forward router syslog and management-plane logs to a centralized logging platform for retention and correlation.
• Monitor DHCP and ARP tables for new devices that immediately begin scanning management ports on the gateway.
• Track outbound traffic from clients whose parental-control policy has changed to detect abuse of loosened restrictions.

How to Mitigate CVE-2026-51710

Immediate Actions Required

• Restrict access to the router's web management interface to trusted administrative hosts on the LAN and disable any WAN-side management exposure.
• Change the router administrator password and audit the parental-control configuration for unauthorized modifications.
• Segment untrusted clients away from the router's management VLAN or subnet where feasible.

Patch Information

No vendor patch is referenced in the NVD entry at time of publication. Users should monitor the TOTOLINK official website and the TOTOLINK product download page for firmware updates addressing this issue on the T6 platform.

Workarounds

• Block inbound traffic to /cgi-bin/cstecgi.cgi from any host that is not an authorized administrator using an upstream firewall or ACL where possible.
• Place the router behind a network segment that filters HTTP requests to the management interface from general user devices.
• Replace affected firmware 4.1.5cu.748_B20211015 with a fixed version once released by the vendor, or migrate to a supported device if no fix is planned.

# Example: restrict router management interface access on an upstream firewall
# Replace 192.0.2.10 with your administrator workstation and 192.0.2.1 with the router
iptables -I FORWARD -p tcp -d 192.0.2.1 --dport 80  -s 192.0.2.10 -j ACCEPT
iptables -I FORWARD -p tcp -d 192.0.2.1 --dport 80  -j DROP
iptables -I FORWARD -p tcp -d 192.0.2.1 --dport 443 -s 192.0.2.10 -j ACCEPT
iptables -I FORWARD -p tcp -d 192.0.2.1 --dport 443 -j DROP