CVE-2026-51701 in TOTOLINK
Summary
by MITRE • 08/31/2026
Incorrect access control in the setMacFilterRules function of TOTOLINK T6 4.1.5cu.748_B20211015 allows unauthenticated attackers to change device access control 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 setMacFilterRules function within TOTOLINK T6 firmware version 4.1.5cu.748_B20211015 represents a critical failure in access control mechanisms, specifically categorized under CWE-284 Improper Access Control. This flaw allows unauthenticated attackers to manipulate device security settings by sending crafted HTTP POST requests to the /cgi-bin/cstecgi.cgi endpoint without requiring valid authentication credentials or session tokens. The absence of proper authorization checks means that any external actor with network access to the management interface can execute administrative functions intended only for authorized users, fundamentally undermining the integrity and confidentiality of the device configuration.
From a technical perspective, the root cause lies in the server-side validation logic associated with the setMacFilterRules API endpoint. Typically, such endpoints should verify user privileges before processing requests that modify firewall rules or access control lists. In this instance, the application fails to validate whether the requester possesses administrative rights, effectively treating unauthenticated traffic as if it originated from a privileged session. This oversight enables attackers to bypass authentication gates entirely, allowing them to inject malicious MAC filter rules into the device’s configuration database. These rules can be designed to block legitimate network traffic or permit unauthorized devices to connect to the local area network, depending on the attacker's intent and payload construction.
The operational impact of this vulnerability is severe, as it directly compromises the security posture of the affected router. By altering MAC filter rules, an adversary can effectively isolate specific users from the network while granting access to rogue devices that would otherwise be blocked by existing policies. This capability facilitates unauthorized network entry points, potentially leading to further exploitation such as lateral movement within the internal network or interception of sensitive data in transit. Furthermore, since routers often serve as gateways between trusted and untrusted networks, compromising their configuration can expose all downstream devices to increased risk, including IoT appliances, workstations, and servers that rely on the router for secure connectivity.
This vulnerability aligns with several entries in the MITRE ATT&CK framework, particularly T1548 Abuse Elevation Control Mechanism, where attackers exploit misconfigurations to bypass access controls, and T1078 Valid Accounts if combined with credential theft scenarios, though here it is exploited without valid accounts due to the lack of authentication checks. It also relates to CWE-269 Improper Privilege Management, as the system fails to enforce appropriate privilege levels for sensitive operations. The ability to modify access control lists remotely via a web interface highlights common weaknesses in embedded device firmware development where security considerations are often secondary to functionality and ease of deployment.
Mitigation strategies must focus on immediate patching and network-level defenses until official updates are applied by the vendor. Administrators should update the TOTOLINK T6 firmware to the latest version that addresses this access control flaw, ensuring that proper authentication checks are enforced for all administrative endpoints. In environments where updating is not immediately feasible, restricting access to the management interface through IP whitelisting or placing it behind a VPN can significantly reduce exposure. Additionally, deploying intrusion detection systems configured to monitor for anomalous POST requests targeting /cgi-bin/cstecgi.cgi may help detect exploitation attempts in real time. Regular security audits and penetration testing of network infrastructure components are essential to identify similar misconfigurations across other devices within the enterprise environment.