CVE-2026-51719 in TOTOLINK
Summary
by MITRE • 08/31/2026
Incorrect access control in the delUrlFilterRules function of TOTOLINK T6 4.1.5cu.748_B20211015 allows unauthenticated attackers to remove URL filtering rules 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 delUrlFilterRules 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 bypass authentication requirements and execute administrative functions that should be restricted to authorized users only. The core technical issue lies in the lack of proper validation checks within the delUrlFilterRules function, which processes HTTP POST requests directed at the /cgi-bin/cstecgi.cgi endpoint without verifying the identity or privileges of the requesting entity. This absence of authentication enforcement means that any external actor with network connectivity to the device can interact directly with this administrative interface component.
From an operational perspective, the ability to remove URL filtering rules has significant implications for network security and content management policies. URL filtering is typically employed by home and small business routers to block access to malicious websites, adult content, or other undesirable categories of internet traffic. By exploiting this vulnerability, an attacker can systematically strip these protective filters from the device configuration. This effectively neutralizes a primary defense mechanism against phishing sites, malware distribution networks, and potentially harmful online content. The removal of such rules leaves connected devices on the network exposed to increased risks of compromise through malicious web destinations that were previously blocked by the router's built-in security features.
This vulnerability aligns with several entries in the MITRE ATT&CK framework, particularly those related to Defense Evasion and Privilege Escalation techniques where attackers manipulate system configurations to avoid detection or maintain access. The exploitation vector involves sending a crafted POST request, which indicates that the attack can be performed remotely over the network without requiring prior authentication credentials. This remote exploitability significantly lowers the barrier for entry, allowing even low-skilled threat actors to compromise the integrity of the router's security posture. The impact extends beyond simple configuration changes; it undermines trust in the device as a secure gateway and may facilitate further lateral movement within a local network if other services are similarly exposed or dependent on these filtering rules for segmentation logic.
Mitigation strategies must focus on addressing both the immediate technical flaw and broader architectural weaknesses. Users should immediately update their TOTOLINK T6 firmware to any version released after this vulnerability was disclosed, as vendors typically patch such access control failures in subsequent releases. In cases where updating is not feasible or possible due to hardware obsolescence, network segmentation becomes critical; placing IoT devices and routers behind additional firewalls with strict ingress filtering can limit exposure. Additionally, administrators should disable remote management features if they are not actively required, thereby reducing the attack surface available to external actors. Regular auditing of router configurations for unauthorized changes is also recommended to detect potential exploitation attempts early.