CVE-2026-51766 in TOTOLINK
Summary
by MITRE • 09/01/2026
Incorrect access control in the setDevReboot function of TOTOLINK T6 4.1.5cu.748_B20211015 allows unauthenticated attackers to reboot the local device and, on a master, fan out reboot commands to mesh slaves 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 device's internal communication architecture. Specifically, the flaw resides in the setDevReboot function, which is responsible for initiating system restarts on the router hardware. This component fails to enforce proper authentication or authorization checks before executing reboot commands. Consequently, any actor with network-level connectivity to the affected MQTT broker service can trigger this functionality without providing valid credentials. The absence of these security controls allows unauthenticated remote attackers to exert significant control over the operational state of the device, undermining the fundamental availability and integrity guarantees expected from enterprise-grade networking equipment.
The technical mechanism of exploitation involves interacting with the cs_broker component via the MQTT protocol. MQTT is a lightweight publish-subscribe messaging transport often used in Internet of Things (IoT) environments for its efficiency and low overhead. In this specific implementation, the broker does not validate whether the sender of a reboot command possesses administrative privileges or any form of valid session token. An attacker can craft a malicious MQTT message containing the appropriate payload to invoke the setDevReboot function. This action forces the local device to restart immediately. The severity is amplified by the mesh networking capabilities inherent in this router model, which allows for coordinated management across multiple nodes in a network topology.
The operational impact of this vulnerability extends beyond simple denial-of-service on a single unit due to its ability to fan out commands to slave devices within a mesh network. When executed on a master node that is configured as part of a mesh setup, the crafted MQTT message can propagate reboot instructions to connected slave nodes. This capability enables an attacker to perform a coordinated distributed denial-of-service attack against the entire local area network segment managed by these routers. By simultaneously or sequentially triggering reboots across multiple devices, the attacker can cause widespread connectivity loss, disrupt critical business operations relying on stable network infrastructure, and potentially create windows of opportunity for further exploitation during the reboot process when security services may be temporarily unavailable or restarting with default configurations.
From a classification perspective, this vulnerability aligns closely with CWE-284, which describes Improper Access Control, as it involves bypassing intended restrictions to perform privileged actions. Furthermore, the use of MQTT for remote command execution and control maps directly to MITRE ATT&CK technique T1565.002, known as Stored Data Manipulation via Client-Side Injection or more broadly under Remote Services such as MQTT being abused for lateral movement or impact. The ability to trigger reboots across a mesh network also reflects aspects of T1499, Endpoint Denial of Service, particularly when considering the cascading effect on multiple endpoints within the local infrastructure.
Mitigation strategies must focus on hardening the access control mechanisms surrounding the MQTT broker and the setDevReboot function. The most effective immediate remediation is to apply vendor-provided firmware updates that patch this specific flaw if available. In environments where updating is not immediately feasible, network segmentation should be implemented to restrict MQTT traffic (typically port 1883 or 8883) to only trusted management subnets and administrative hosts. Additionally, enabling TLS encryption for MQTT connections can help prevent eavesdropping and ensure that message integrity is maintained, although it does not directly solve the authentication flaw unless client certificate mutual authentication is strictly enforced. Security monitoring should also be configured to detect anomalous spikes in MQTT traffic or repeated reboot events originating from untrusted sources within the network perimeter.