CVE-2026-51764 in TOTOLINK
Summary
by MITRE • 09/01/2026
Incorrect access control in the recvSlaveCloudCheckStatus function of TOTOLINK T6 4.1.5cu.748_B20211015 allows unauthenticated attackers to overwrite cloud-result tracking files 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 router firmware version 4.1.5cu.748_B20211015 represents a critical failure in access control mechanisms within the device's cloud connectivity subsystem. Specifically, the flaw resides in the recvSlaveCloudCheckStatus function, which is responsible for processing status checks and updates from the manufacturer’s cloud infrastructure via MQTT protocol. This component acts as an intermediary between the local network environment and external cloud services, handling sensitive operational data that dictates how the router reports its health and configuration state to remote management platforms. The absence of proper authentication or authorization checks within this specific function allows any entity capable of reaching the cs_broker service on the network to interact with it without valid credentials. This lack of enforcement is a fundamental design error that undermines the integrity of the communication channel between the device and its cloud backend, creating an open vector for malicious actors operating within the same local area network or potentially over the internet if port forwarding rules are misconfigured.
From a technical perspective, this vulnerability enables unauthenticated attackers to overwrite cloud-result tracking files by injecting crafted MQTT messages into the cs_broker component. These tracking files likely contain metadata regarding previous connection attempts, status reports, and synchronization states that the router uses to maintain consistency with the manufacturer’s dashboard. By manipulating these files through maliciously formatted MQTT payloads, an attacker can alter the perceived state of the device in the cloud management interface. This capability goes beyond simple denial of service; it allows for persistent manipulation of the device's reported status. For instance, an attacker could falsify connectivity logs to hide their own network activities or disrupt automated monitoring systems that rely on accurate data from these tracking files. The exploitation requires only the ability to send a specific MQTT message to the targeted port and function, making it relatively straightforward to execute for any adversary with local network access who possesses basic networking tools capable of crafting custom protocol messages.
The operational impact of this vulnerability is significant for both individual users relying on remote management features and organizations using these devices in enterprise environments where centralized monitoring is critical. If an attacker successfully overwrites the cloud-result tracking files, they can obscure malicious activities such as unauthorized configuration changes, data exfiltration attempts, or the installation of backdoors within the router’s firmware. This obscuration makes incident detection and forensic analysis considerably more difficult for administrators who rely on cloud-based logs to identify anomalies. Furthermore, if the cloud management platform uses these tracking files to trigger automated responses or alerts, an attacker could potentially suppress security warnings or generate false positives that distract legitimate operators. In a broader context, compromised routers often serve as gateways for lateral movement within a network; therefore, undermining the integrity of their reporting mechanisms facilitates deeper infiltration and reduces the likelihood of early detection by security operations centers monitoring cloud-connected endpoints.
This flaw aligns with CWE-284, which describes Improper Access Control, specifically highlighting failures in authorization checks that allow unauthorized actions to be performed. Additionally, the exploitation technique maps to MITRE ATT&CK techniques related to Command and Scripting Interpreter abuse or potentially T1071 Application Layer Protocol if viewed as a means of maintaining persistent communication channels while evading detection through log manipulation. The use of MQTT for this interaction also touches upon CWE-923 regarding Improper Restriction of Communication between Components, as the internal component cs_broker fails to validate the source or intent of incoming messages before processing them into sensitive file structures.
To mitigate this vulnerability, users should immediately update their TOTOLINK T6 firmware to a patched version that addresses the access control deficiencies in the recvSlaveCloudCheckStatus function if such an update is available from the manufacturer. In environments where updates are not yet deployed or applicable, network segmentation strategies should be implemented to restrict MQTT traffic on the affected ports to only trusted internal management subnets. Firewall rules can also be configured to block inbound connections to the cs_broker service from untrusted networks, effectively isolating the vulnerable component from potential external attackers. Additionally, administrators should enable strict logging and monitor for unusual patterns in cloud connectivity logs that might indicate attempts to manipulate tracking files, although this is a compensatory measure rather than a fix for the underlying code flaw. Regular audits of router configurations and disabling unnecessary remote management features can further reduce the attack surface associated with such internet-facing or network-accessible services.