CVE-2026-51702 in TOTOLINK
Summary
by MITRE • 08/31/2026
Incorrect access control in the setIpPortFilterRules function of TOTOLINK T6 4.1.5cu.748_B20211015 allows unauthenticated attackers to alter firewall policies via sending a crafted POST request to /cgi-bin/cstecgi.cgi.
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Analysis
by VulDB Data Team • 08/31/2026
The vulnerability identified in the setIpPortFilterRules function within TOTOLINK T6 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 manipulate firewall policies by sending crafted POST requests to the /cgi-bin/cstecgi.cgi endpoint. The root cause lies in the application's insufficient validation of user privileges before executing administrative functions that modify network security configurations. In a properly secured system, any request intended to alter firewall rules must be preceded by an authenticated session with appropriate administrator-level permissions. However, due to this implementation error, the server processes these modification requests without verifying the identity or authorization level of the requester, effectively bypassing authentication controls entirely.
From a technical perspective, the vulnerability exploits the lack of state verification and privilege checks within the CGI script handling IP port filter rules. The setIpPortFilterRules function is designed to update packet filtering parameters that dictate which traffic is allowed or denied through the router's network interface. By sending a specifically crafted HTTP POST request containing maliciously formatted data, an attacker can inject arbitrary firewall rules into the device configuration. This capability enables the modification of access control lists without any form of authentication, demonstrating a severe breakdown in security architecture where sensitive administrative functions are exposed to public or untrusted networks. The attack vector is remote and requires no prior interaction with the system other than network connectivity to the target device's management interface.
The operational impact of this vulnerability is significant, as it directly compromises the integrity and confidentiality of network traffic managed by the router. An attacker who successfully exploits this flaw can disable existing firewall protections, open specific ports for unauthorized access, or redirect traffic through malicious intermediaries. This effectively neutralizes one of the primary security layers provided by home and small business routers, leaving connected devices vulnerable to intrusion, data exfiltration, and further exploitation within the local network segment. Furthermore, because the attacker can alter filtering rules at will, they may also facilitate persistent backdoors or covert communication channels that are difficult for standard monitoring tools to detect due to their integration into legitimate firewall configurations.
This vulnerability aligns with several entries in the MITRE ATT&CK framework, particularly those related to privilege escalation and defense evasion through configuration manipulation. It exemplifies how improper access control can lead to unauthorized system modifications, a common pattern in IoT device vulnerabilities where security is often secondary to functionality during development. The ability to modify firewall rules remotely without authentication places this flaw in the category of high-severity issues that require immediate attention from network administrators and vendors alike.
Mitigation strategies must focus on both immediate remediation and long-term architectural improvements. Users should immediately update their TOTOLINK T6 firmware to a version where this access control issue has been resolved, ensuring that all administrative functions are properly gated behind strong authentication mechanisms. Network segmentation can also serve as an interim protective measure by isolating the router's management interface from untrusted networks or restricting access to trusted IP addresses only via ACLs on upstream devices if available. Additionally, vendors must implement rigorous code review processes and adopt secure development lifecycle practices that include automated testing for common vulnerabilities such as broken authentication and insufficient authorization checks before releasing firmware updates. Regular security audits of embedded web interfaces are essential to prevent similar flaws in future releases.