CVE-2026-51659 in TOTOLINK
Summary
by MITRE • 08/28/2026
Incorrect access control in the getUrlFilterRules function of TOTOLINK T6 4.1.5cu.748_B20211015 allows unauthenticated attackers to obtain DMZ configuration information via sending a crafted POST request to /cgi-bin/cstecgi.cgi.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 08/28/2026
The vulnerability identified in the TOTOLINK T6 router, specifically within version 4.1.5cu.748_B20211015, represents a critical failure in access control mechanisms that allows unauthenticated actors to extract sensitive network configuration data. The flaw resides in the getUrlFilterRules function, which is exposed through the device's web management interface via the endpoint /cgi-bin/cstecgi.cgi. This component is designed to retrieve and return filter rules governing internet connectivity and security policies, but it lacks proper authentication checks or session validation before processing incoming requests. Consequently, any external user with network access to the router can interact directly with this function without needing valid administrative credentials.
From a technical perspective, the issue stems from an improper implementation of authorization logic within the CGI script handling POST requests. When an attacker sends a crafted POST request to the specified endpoint, the server processes the command and returns the current DMZ (Demilitarized Zone) configuration details along with other filter rules. This behavior indicates that the function does not verify whether the requester has been authenticated or possesses the necessary privileges to view such sensitive information. The absence of these checks creates a direct path for data exfiltration, bypassing standard security boundaries intended to protect administrative settings from unauthorized access.
The operational impact of this vulnerability is significant, as it exposes critical network topology and security policy details to potential adversaries. By obtaining DMZ configuration information, an attacker can identify which internal IP addresses are exposed directly to the internet without NAT protection. This knowledge facilitates targeted attacks against specific devices within the local network, such as servers or IoT devices that may have weaker inherent security postures. Furthermore, understanding the existing filter rules allows attackers to map out allowed traffic patterns and potentially craft packets that evade detection by manipulating protocol headers or port numbers in ways consistent with the known open ports and protocols.
This vulnerability aligns closely with CWE-284, which describes Improper Access Control, as it involves a failure to enforce proper authorization policies for sensitive functions. Additionally, from an offensive security standpoint, this behavior is characteristic of techniques found in MITRE ATT&CK framework under T1506, specifically the component related to Defense Discovery where adversaries gather information about defensive mechanisms like firewalls and intrusion detection systems. The ability to retrieve these configurations remotely without authentication significantly lowers the barrier for entry, allowing less sophisticated attackers to perform reconnaissance that would typically require higher privilege levels or physical access.
Mitigation strategies should focus on immediate remediation of the underlying code defect by enforcing strict authentication checks before any sensitive configuration data is retrieved. Developers must ensure that all administrative functions within the CGI interface validate user sessions and verify role-based permissions prior to execution. In addition to patching, network administrators are advised to restrict access to the router's management interface through IP whitelisting or VPN tunnels where possible, reducing the attack surface exposed to untrusted networks. Until a firmware update is available, disabling remote administration features if they are not strictly necessary can further limit exposure to this type of unauthorized data retrieval attempt.