CVE-2026-51629 Overview
CVE-2026-51629 is an incorrect access control vulnerability in the getStaticDhcpRules function of the TOTOLINK T6 router running firmware version 4.1.5cu.748_B20211015. Unauthenticated attackers on an adjacent network can retrieve static DHCP reservation rules by sending a crafted POST request to /cgi-bin/cstecgi.cgi. The flaw exposes network configuration data without requiring credentials or user interaction. It is categorized under [CWE-284] Improper Access Control.
Critical Impact
Adjacent-network attackers can enumerate static DHCP mappings, revealing MAC-to-IP bindings and internal device identifiers that support further reconnaissance and lateral movement.
Affected Products
- TOTOLINK T6 router
- Firmware version 4.1.5cu.748_B20211015
- CGI endpoint /cgi-bin/cstecgi.cgi
Discovery Timeline
- 2026-08-28 - CVE-2026-51629 published to NVD
- 2026-09-01 - Last updated in NVD database
Technical Details for CVE-2026-51629
Vulnerability Analysis
The TOTOLINK T6 web management interface exposes administrative functionality through the /cgi-bin/cstecgi.cgi handler. The getStaticDhcpRules function within this handler returns the router's static DHCP reservation configuration. According to the advisory, the function does not enforce authentication or session validation before returning configuration data.
An attacker on the same Layer 2 network segment can issue a POST request that invokes this function and receive the router's static DHCP rules in the response. These rules typically contain MAC addresses, reserved IP addresses, and human-readable device labels assigned by the administrator.
The exposure supports pre-attack reconnaissance. Attackers can map internal hosts, identify high-value systems by hostname or label, and plan targeted follow-on activity such as ARP spoofing, DNS redirection, or credential harvesting against specific endpoints.
Root Cause
The root cause is a missing authorization check on the getStaticDhcpRules handler [CWE-284]. The CGI dispatcher routes requests to the function based on a topicurl or equivalent parameter in the POST body without verifying that the caller holds a valid administrative session. The function treats any well-formed request as authorized.
Attack Vector
The vulnerability requires network adjacency, meaning the attacker must reach the router's LAN or Wi-Fi interface. A guest Wi-Fi client, a compromised endpoint, or a device on a shared broadcast segment can send the crafted POST request directly. No credentials, tokens, or user interaction are required.
The attacker sends an HTTP POST to http://<router_ip>/cgi-bin/cstecgi.cgi with a JSON body specifying the getStaticDhcpRules action. The device returns the static DHCP configuration in the response body. Full exploitation details are described in the referenced TOTOLINK Vendor Coordination Guide.
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Stop Identity AttacksDetection Methods for CVE-2026-51629
Indicators of Compromise
- Unexpected POST requests to /cgi-bin/cstecgi.cgi from LAN or guest-network clients that do not correspond to legitimate administrator sessions.
- Requests to cstecgi.cgi referencing the getStaticDhcpRules action or equivalent topicurl value from unauthenticated sources.
- Anomalous traffic to the router management interface originating from guest VLANs or Wi-Fi client isolation zones.
Detection Strategies
- Enable HTTP access logging on the router where supported and forward logs to a central collector for review.
- Deploy network sensors on management VLANs to alert on POST traffic to cstecgi.cgi from non-administrative hosts.
- Correlate router configuration read attempts with subsequent scanning or ARP anomalies on the same segment.
Monitoring Recommendations
- Baseline normal administrative traffic to the router and alert on deviations in source IP, frequency, or request body content.
- Monitor for reconnaissance patterns such as sequential CGI action enumeration against /cgi-bin/cstecgi.cgi.
- Track guest-network clients that initiate connections to the router management IP address.
How to Mitigate CVE-2026-51629
Immediate Actions Required
- Restrict access to the router web management interface to a dedicated management VLAN or trusted admin hosts only.
- Disable remote management over Wi-Fi and enable client isolation on guest wireless networks.
- Check the TOTOLINK Firmware Download Page for updated firmware addressing the affected version.
- Rotate any credentials or device identifiers that may have been inferred from exposed DHCP reservations.
Patch Information
At the time of publication, no vendor patch is referenced in the NVD entry for firmware 4.1.5cu.748_B20211015. Administrators should monitor the TOTOLINK Official Website and the Vendor Coordination Guide for firmware updates that add authorization checks to the getStaticDhcpRules handler.
Workarounds
- Place the router management interface on a segregated VLAN unreachable from guest and IoT networks.
- Apply firewall rules on upstream infrastructure to block inbound HTTP traffic to the router from untrusted segments.
- Replace the affected device with hardware that receives active security maintenance if a firmware fix does not become available.
# Configuration example: restrict management access using iptables on an upstream gateway
iptables -A FORWARD -s 192.168.10.0/24 -d 192.168.1.1 -p tcp --dport 80 -j DROP
iptables -A FORWARD -s 192.168.20.0/24 -d 192.168.1.1 -p tcp --dport 80 -j DROP
iptables -A FORWARD -s 192.168.1.10/32 -d 192.168.1.1 -p tcp --dport 80 -j ACCEPT
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
