CVE-2026-51660 in TOTOLINK
Summary
by MITRE • 08/28/2026
Incorrect access control in the getIpPortFilterRules function of TOTOLINK T6 4.1.5cu.748_B20211015 allows unauthenticated attackers to obtain IP and port filtering 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 TOTOLINK T6 router firmware version 4.1.5cu.748_B20211015 represents a critical failure in access control mechanisms within the device's web management interface. Specifically, the flaw resides in the getIpPortFilterRules function, which is responsible for retrieving network filtering configurations such as IP and port rules used to manage traffic flow and security policies on the local area network. This component fails to enforce proper authentication checks before processing requests intended to expose sensitive configuration data. As a result, any unauthenticated actor who can reach the device's web interface over the network can exploit this weakness without needing valid credentials or session tokens.
The technical mechanism of exploitation involves sending a crafted POST request directly to the /cgi-bin/cstecgi.cgi endpoint, which serves as the primary gateway for executing administrative commands on many embedded devices based on similar firmware architectures. By targeting the getIpPortFilterRules function through this interface, an attacker can trigger the retrieval and transmission of internal filtering rules back to their machine. These rules typically contain detailed information about allowed or blocked IP addresses, specific port numbers, and potentially other network segmentation policies that define how traffic is permitted or denied within the local environment. The lack of authentication verification at this stage indicates a fundamental oversight in the security design of the CGI handler logic.
The operational impact of this vulnerability extends beyond simple data leakage. By obtaining these filtering rules, an attacker gains significant insight into the defensive posture of the target network. This information can be used to map out which services are exposed to external traffic and which internal hosts or ports are protected by firewall rules. Such knowledge facilitates more effective lateral movement within a compromised network segment, as the attacker can identify gaps in coverage where specific protocols or devices remain unprotected due to overly permissive filtering configurations. Furthermore, understanding these rules allows for precise evasion techniques that bypass existing security controls during subsequent attack phases.
This vulnerability aligns with CWE-284, which describes Improper Access Control, specifically highlighting failures where authorization checks are omitted or incorrectly implemented in critical functions. In the context of the MITRE ATT&CK framework, this behavior corresponds to T1506, Defense Discovery, as it enables adversaries to gather information about security mechanisms and network architecture that could hinder their operations if left undetected. The ability to extract configuration details remotely without authentication significantly lowers the barrier for entry in automated scanning campaigns targeting vulnerable IoT devices across the internet.
Mitigation strategies should prioritize immediate patching of the router firmware to a version where this access control flaw has been remediated by the vendor. If an update is not immediately available, network administrators can implement compensating controls such as restricting access to the web management interface via IP whitelisting or placing it behind a secure administrative VPN. Additionally, deploying intrusion detection systems that monitor for suspicious POST requests targeting /cgi-bin/cstecgi.cgi with parameters related to rule retrieval can help detect exploitation attempts in real-time. Regular audits of exposed services and disabling unnecessary remote administration features are also recommended to reduce the attack surface associated with embedded web interfaces.