CVE-2026-51760 in TOTOLINK
Summary
by MITRE • 09/01/2026
Incorrect access control in the informSyncUpgfw function of TOTOLINK T6 4.1.5cu.748_B20211015 allows unauthenticated attackers to mass-trigger firmware update activity across 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 routers running version 4.1.5cu.748_B20211015 represents a critical failure in access control mechanisms within the device's mesh networking architecture. Specifically, the flaw resides in the informSyncUpgfw function, which is responsible for synchronizing firmware update states across devices in a mesh network. This component interacts with the cs_broker, an MQTT-based message broker that facilitates communication between the router’s internal services and connected slave nodes. The core technical deficiency lies in the absence of proper authentication or authorization checks when processing incoming messages intended to trigger synchronization events. Consequently, any entity capable of reaching the MQTT endpoint can inject malicious payloads without providing valid credentials, effectively bypassing security controls designed to restrict administrative actions to authorized users only.
From a technical perspective, this vulnerability allows unauthenticated attackers to mass-trigger firmware update activity across all mesh slave devices connected to the primary router. By sending a crafted MQTT message to the cs_broker component, an attacker can force the system into a state where it attempts to apply or synchronize firmware updates indiscriminately. This action is not limited by user privileges and does not require prior authentication, making it accessible to any network participant who has access to the relevant communication channels. The ability to trigger these operations remotely exploits the trust relationship inherent in mesh networking protocols, where slave devices are expected to follow commands from the central controller without rigorous verification of command origin or intent.
The operational impact of this vulnerability is severe and multifaceted. First, it enables a denial-of-service condition by forcing multiple devices into an update cycle simultaneously. Firmware updates typically involve rebooting devices and re-establishing network connections, which can lead to significant downtime for all affected nodes in the mesh topology. This disruption affects not only local connectivity but also any external services relying on these devices. Second, if the attacker controls or manipulates the firmware image referenced during this forced synchronization process, they could potentially deploy malicious code across the entire mesh network. This would result in a widespread compromise of device integrity, allowing for persistent backdoors, data exfiltration, or use of the compromised devices as part of a botnet. The lack of authentication means that even external attackers with limited network access can exploit this flaw if they can intercept or inject traffic into the MQTT broker interface.
This vulnerability aligns with CWE-284, which describes Improper Access Control, specifically highlighting failures in authorization checks for critical functions. Furthermore, it maps to MITRE ATT&CK techniques related to Initial Access and Execution via remote services, as well as potential Persistence mechanisms if malicious firmware is deployed. The exploitation vector leverages the MQTT protocol’s publish-subscribe model, where message brokers often struggle with default configurations that prioritize ease of use over security, such as allowing anonymous access or lacking topic-level permissions.
Mitigation strategies must address both immediate remediation and long-term architectural improvements. Users should immediately apply any available firmware updates provided by TOTOLINK that patch this specific vulnerability in the informSyncUpgfw function. If no official patch is yet available, network administrators should isolate affected devices from untrusted networks and restrict MQTT broker access to localhost or authenticated internal services only. Implementing strong authentication mechanisms for all MQTT topics, particularly those related to system management and firmware updates, is essential. Additionally, deploying intrusion detection systems that monitor for anomalous MQTT traffic patterns can help identify exploitation attempts in real-time. Future development should enforce strict role-based access control on all administrative functions within the mesh network protocol stack to prevent unauthorized entities from triggering critical state changes.