CVE-2026-51757 in TOTOLINK
Summary
by MITRE • 09/01/2026
Incorrect access control in the meshSlaveUpdate function of TOTOLINK T6 4.1.5cu.748_B20211015 allows unauthenticated attackers to start a firmware download or flash workflow on the slave 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 router firmware version 4.1.5cu.748_B20211015 represents a critical failure in access control mechanisms within the meshSlaveUpdate function. This flaw specifically affects the cs_broker component, which is responsible for handling communication between devices in a mesh network configuration. The core issue lies in the absence of proper authentication checks before initiating sensitive operational workflows. An unauthenticated attacker who can reach the affected device over the network can exploit this deficiency by sending a specially crafted MQTT message to the broker service. This action triggers the firmware download or flashing process on the slave device without requiring valid credentials, effectively bypassing security controls designed to prevent unauthorized modifications to system software.
From a technical perspective, the vulnerability stems from insufficient validation of user privileges within the meshSlaveUpdate function. In secure implementations, any request to update firmware should require explicit authentication and authorization checks to ensure that only authorized administrators can initiate such high-impact operations. The cs_broker component fails to enforce these restrictions, allowing external actors to inject commands directly into the system's update pipeline. This type of flaw is commonly categorized under CWE-284 Improper Access Control, as it allows unauthorized entities to perform actions reserved for privileged users. Furthermore, this vulnerability aligns with MITRE ATT&CK technique T1530 Data from Information Repositories or potentially T1059 Command and Scripting Interpreter if the MQTT message contains executable payloads, though in this specific case, it primarily facilitates unauthorized firmware updates which can lead to further compromise through malicious code injection.
The operational impact of this vulnerability is severe due to the nature of firmware flashing operations. By forcing a slave device to download or flash new firmware via an unauthenticated request, attackers can potentially install modified versions of the operating system that contain backdoors, malware, or other malicious modifications. This could result in complete loss of confidentiality, integrity, and availability for devices within the mesh network. Attackers may use this vector to establish persistent access, exfiltrate sensitive data processed by these routers, or disrupt network operations entirely. Since mesh networks often involve multiple interconnected devices, compromising one slave device through this method can serve as a foothold for lateral movement across the entire local area network, amplifying the potential damage significantly beyond a single endpoint.
Mitigation strategies must focus on immediate remediation and long-term architectural improvements. The most effective solution is to apply vendor-provided firmware updates that patch the access control logic in the meshSlaveUpdate function. Administrators should verify their current version against known vulnerable releases and update promptly upon availability of fixed versions. In environments where updating is not immediately feasible, network segmentation can help isolate affected devices from untrusted networks or users who might attempt exploitation. Additionally, implementing strict firewall rules to restrict MQTT traffic on port 1883 (or relevant broker ports) to only trusted IP addresses reduces the attack surface significantly. Future development should enforce principle of least privilege by ensuring all administrative functions require multi-factor authentication and role-based access control checks before execution. Regular security audits focusing on API endpoints and message brokers are essential to detect similar misconfigurations early in the software lifecycle.