CVE-2026-51655 in TOTOLINK
Summary
by MITRE • 08/28/2026
Incorrect access control in the getMacFilterRules function of TOTOLINK T6 4.1.5cu.748_B20211015 allows unauthenticated attackers to obtain MAC filter rules via sending a crafted POST request to /cgi-bin/cstecgi.cgi.
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Analysis
by VulDB Data Team • 08/28/2026
The vulnerability identified in the getMacFilterRules function of TOTOLINK T6 router firmware version 4.1.5cu.748_B20211015 represents a critical failure in access control mechanisms, specifically classified under CWE-284: Improper Access Control. This flaw allows unauthenticated attackers to retrieve sensitive network configuration data without requiring valid credentials or session tokens. The core technical issue lies within the handling of HTTP POST requests directed at the /cgi-bin/cstecgi.cgi endpoint. In a properly secured system, functions responsible for retrieving administrative settings such as MAC filter rules should enforce strict authentication checks and verify user privileges before executing any logic that exposes internal state information. However, in this specific firmware version, the getMacFilterRules function fails to validate whether the incoming request originates from an authenticated administrator or an external unauthenticated entity. This oversight effectively bypasses the intended security boundary, treating requests from anonymous sources with the same level of trust as those from authorized users.
From a technical perspective, the vulnerability exploits the lack of input validation and authorization checks within the Common Gateway Interface (CGI) script that processes administrative commands. When an attacker sends a crafted POST request to /cgi-bin/cstecgi.cgi containing parameters designed to invoke the getMacFilterRules function, the server executes the logic without verifying the requester's identity. This behavior is indicative of broken object level authorization or missing function level access control, where specific API endpoints are exposed publicly rather than being restricted to authenticated sessions. The ability to retrieve MAC filter rules provides attackers with detailed insights into the network segmentation policies configured by the administrator. These rules typically define which devices are permitted or denied connectivity based on their Media Access Control addresses, serving as a primary layer of access control for local networks.
The operational impact of this vulnerability is significant, particularly in home and small office environments where routers often serve as the sole perimeter defense device. By obtaining MAC filter rules, an attacker can map out which devices are actively protected by filtering policies and which might be left open or whitelisted. This information facilitates targeted attacks against specific endpoints that may have weaker security postures compared to others on the network. Furthermore, knowledge of these rules allows for potential evasion techniques; attackers can spoof MAC addresses that match those already permitted in the filter list, thereby gaining unauthorized access to restricted network segments without triggering alerts or being blocked by the router's built-in protections. This undermines the integrity and confidentiality of the local area network, potentially leading to further compromise of connected devices such as IoT gadgets, personal computers, and mobile phones.
In terms of industry standards mapping, this vulnerability aligns with MITRE ATT&CK technique T1087: Account Discovery, specifically within the context of Local Accounts or Network Configuration discovery. The attacker is effectively enumerating configuration details to understand the security landscape before launching more intrusive exploits. Additionally, it falls under CWE-200: Exposure of Sensitive Information to an Unauthorized Actor, as the sensitive network policy data is disclosed without proper authorization controls. The lack of authentication for a critical administrative function also reflects weaknesses in session management and access control design principles outlined in OWASP guidelines for web application security.
To mitigate this vulnerability, users should immediately update their TOTOLINK T6 router firmware to the latest version released by the manufacturer, which likely includes patches addressing these access control deficiencies. If an updated firmware is not yet available or cannot be applied due to operational constraints, temporary mitigations include disabling remote management features if they are enabled, as this restricts exposure of administrative interfaces to external networks. Additionally, changing default administrator passwords and ensuring that only trusted IP addresses can access the router's web interface via firewall rules on upstream devices can reduce the attack surface. Network segmentation strategies should also be reviewed; relying solely on MAC filtering is insufficient for robust security due to its susceptibility to spoofing, so it should be supplemented with stronger authentication mechanisms and encryption protocols where applicable. Regular monitoring of network traffic for unusual POST requests to CGI endpoints may also help in detecting exploitation attempts in real-time.