CVE-2026-51767 in TOTOLINK
Summary
by MITRE • 09/01/2026
Incorrect access control in the recvClearPairCfg function of TOTOLINK T6 4.1.5cu.748_B20211015 allows unauthenticated attackers to reset pairing state and reboot the device via sending a crafted MQTT message to the cs_broker component.
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Analysis
by VulDB Data Team • 09/01/2026
The vulnerability identified in TOTOLINK T6 firmware version 4.1.5cu.748_B20211015 represents a critical failure in access control mechanisms within the network device's communication subsystem. Specifically, the flaw resides in the recvClearPairCfg function, which is responsible for handling configuration clearing and pairing state management requests via MQTT protocols. This component interacts with the cs_broker service, acting as an intermediary for message routing between internal system modules and external clients. The core technical deficiency lies in the absence of proper authentication checks before processing these specific administrative commands. Consequently, any entity capable of reaching the device's network interface can invoke this function without providing valid credentials or session tokens, effectively bypassing intended security boundaries designed to protect sensitive configuration states.
From a technical perspective, the exploitation vector involves sending a specially crafted MQTT message directly to the cs_broker component. Because the recvClearPairCfg endpoint does not validate the identity of the sender prior to execution, an unauthenticated attacker can trigger the function at will. The operational consequence of this action is severe: it forces the device to reset its pairing state and subsequently reboot. This behavior disrupts normal network operations by breaking established connections with paired devices or management platforms that rely on persistent session states. Furthermore, the forced reboot introduces a denial-of-service condition, rendering the router temporarily unavailable until the system completes its restart cycle. In environments where high availability is critical, such as industrial IoT deployments or secure home networks, this instability can lead to significant operational downtime and potential data loss during reconnection processes.
This vulnerability aligns with CWE-284, which describes Improper Access Control, specifically highlighting scenarios where authorization checks are missing for sensitive operations. Additionally, the exploitation technique maps closely to MITRE ATT&CK techniques related to Command and Scripting Interpreter abuse or Service Stop/Start actions, as the attacker leverages a legitimate service interface to disrupt system availability. The ability to reset pairing states also touches upon CWE-602, Client-Side Injection, if interpreted broadly in terms of manipulating client-side state through untrusted input, though it is more accurately classified under privilege escalation or unauthorized configuration modification due to the administrative nature of the command being executed remotely without authentication.
Mitigation strategies must focus on implementing robust access control policies within the MQTT broker and its associated handler functions. Developers should enforce strict authentication requirements for all administrative endpoints, ensuring that only authorized users with valid credentials can invoke commands like recvClearPairCfg. Implementing role-based access control (RBAC) would further restrict these operations to specific user groups designated for device management. Additionally, input validation mechanisms should be strengthened to verify the integrity and origin of MQTT messages before they are processed by critical system functions. For immediate risk reduction in deployed environments, network segmentation is recommended to isolate IoT devices from untrusted networks, limiting exposure to potential attackers who might attempt to exploit this flaw over local or wide area networks until a firmware patch addressing these access control deficiencies is released and applied.