CVE-2026-51651 in TOTOLINK
Summary
by MITRE • 08/28/2026
Incorrect access control in the getSmartQosCfg function of TOTOLINK T6 4.1.5cu.748_B20211015 allows unauthenticated attackers to obtain Smart QoS configuration and 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 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 getSmartQosCfg function, which is designed to retrieve Quality of Service configuration parameters and associated rules for network traffic prioritization. Under normal operational conditions, such administrative functions should require valid authentication credentials to ensure that only authorized users can view or modify sensitive network settings. However, due to an implementation error, this specific endpoint fails to enforce proper authorization checks before processing requests. This oversight allows unauthenticated attackers to interact with the function directly without needing to log in first.
The technical mechanism of exploitation involves sending a crafted POST request to the /cgi-bin/cstecgi.cgi script, which serves as the gateway for various administrative commands on the router's embedded web server. By targeting the getSmartQosCfg endpoint through this interface, an attacker can bypass authentication entirely and retrieve detailed information about how the network prioritizes different types of traffic. This includes specific rules defining bandwidth allocation, priority levels for applications or devices, and potentially other configuration details that define the operational behavior of the local area network. The lack of session validation or token verification means that any external actor with network access to the router's management interface can execute this request successfully.
The operational impact of this vulnerability is significant as it leads to a severe information disclosure scenario. Smart QoS configurations often contain implicit insights into the internal network topology, such as which devices are considered critical and how traffic flows are managed between different subnets or interfaces. An attacker gaining access to these rules can map out the network structure with greater precision than previously possible through general reconnaissance alone. This intelligence can be leveraged for further attacks, including targeted denial-of-service attempts against high-priority services, manipulation of traffic shaping policies to degrade performance for specific targets, or simply understanding the security posture of the environment to plan more sophisticated intrusions. The exposure of administrative configuration details also aids in identifying other potential misconfigurations that might exist within the device's firmware.
From a classification perspective, this vulnerability aligns with CWE-284, which describes Improper Access Control, specifically where access control is not properly enforced for sensitive functions. It also relates to CWE-200, Information Exposure, as it results in the unauthorized disclosure of information that could be detrimental to security. In terms of adversary tactics, this exploitation technique corresponds to ATT&CK tactic T1592, Gather Victim Host Information, and specifically sub-technique T1592.004, which involves gathering network configuration details from a target system. The ability to extract these settings without authentication places the vulnerability in the initial access or discovery phase of an attack chain, depending on whether the attacker is already inside the local network perimeter.
Mitigation strategies for this issue primarily involve applying vendor-provided firmware updates that address the authorization logic within the getSmartQosCfg function. Administrators should ensure their devices are running patched versions where proper authentication checks have been implemented to restrict access to administrative endpoints. In cases where immediate patching is not feasible, network segmentation can help limit exposure by ensuring that the management interface of routers is only accessible from trusted internal subnets rather than being exposed to untrusted networks or the internet. Additionally, disabling remote administration features if they are not strictly necessary reduces the attack surface available to potential attackers seeking to exploit this flaw remotely. Regular auditing of device configurations and monitoring for unusual access patterns can also aid in detecting attempts to probe these vulnerable endpoints before successful exploitation occurs.