CVE-2026-51743 in TOTOLINK
Summary
by MITRE • 09/01/2026
Incorrect access control in the guest_wifi_sync function of TOTOLINK T6 4.1.5cu.748_B20211015 allows unauthenticated attackers to disable guest virtual AP interfaces 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 internal communication architecture. Specifically, the flaw resides in the guest_wifi_sync function, which is responsible for managing and synchronizing settings related to guest wireless network interfaces. This component interacts with an MQTT broker service known as cs_broker, which facilitates message-based communication between various system modules. The core issue arises from the absence of proper authentication or authorization checks when processing incoming messages directed at this synchronization endpoint. Consequently, any entity capable of reaching the MQTT broker can execute commands that alter critical network configurations without providing valid credentials.
From a technical perspective, an unauthenticated attacker who has network access to the router's internal services can exploit this weakness by sending a specifically crafted MQTT message. This malicious payload triggers the guest_wifi_sync function with parameters designed to disable or manipulate guest virtual AP interfaces. Since the system does not verify the identity of the sender before executing these administrative actions, the vulnerability allows for remote configuration manipulation without any form of user interaction or privilege escalation beyond basic network connectivity. This type of flaw is characteristic of insecure direct object references where internal functions are exposed via message brokers without adequate security boundaries, aligning with CWE-284 Improper Access Control and CWE-798 Use of Hard-coded Credentials if default MQTT topics lack authentication by design.
The operational impact of this vulnerability is significant for network administrators and end-users relying on the guest Wi-Fi feature. By disabling the guest virtual AP interface through an unauthenticated attack, an adversary can effectively cut off access to the isolated guest network segment. This disruption not only causes a denial of service for legitimate guests but may also indicate deeper instability within the router's firmware logic. Furthermore, if the synchronization function interacts with other security policies or firewall rules associated with the guest network, its manipulation could inadvertently weaken the overall segmentation strategy, potentially allowing lateral movement from the guest VLAN to the trusted internal network depending on how strictly the isolation is enforced at the kernel level.
This vulnerability maps directly to MITRE ATT&CK techniques involving configuration changes and service disruption. It falls under T1562 Impair Defenses as it disables a security feature (guest isolation) and can be classified under T1078 Valid Accounts if the MQTT broker relies on weak or default credentials, though in this case, no account is required at all due to the lack of authentication checks entirely. The attack vector leverages network-based interactions with internal services, highlighting risks associated with exposing management interfaces or inter-process communication channels without strict access controls.
Mitigation strategies for this vulnerability primarily involve applying vendor-provided firmware updates that patch the guest_wifi_sync function and enforce proper authentication on MQTT broker endpoints. Until an update is available, administrators should isolate the router's management interface from untrusted networks and disable any unnecessary internal services or ports if possible. Network segmentation policies should be reviewed to ensure that even if a single device compromises the router's configuration capabilities, the blast radius remains contained within the local network segment. Additionally, monitoring for unusual MQTT traffic patterns on the host system can aid in early detection of exploitation attempts targeting this specific function.