Description

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.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "9.8",
  "pubDate": "2026-09-01T14:17:36.407Z",
  "pubdate": "2026-09-01T14:17:36.407Z",
  "executiveSummary": "This vulnerability involves an incorrect access control flaw within the TOTOLINK T6 router firmware (version 4.1.5cu.748_B20211015) that permits unauthorized firmware update operations.\nThe vulnerability manifests in the 'informSyncUpgfw' function, which fails to adequately validate the authenticity or authorization of incoming requests.\nUnauthenticated remote attackers can exploit this by injecting crafted MQTT messages directed at the 'cs_broker' component, effectively forcing mesh slave devices to initiate a firmware update process.\nThe primary risk implication is the potential for mass-disruption of the mesh network, forced downtime, or the deployment of arbitrary, potentially malicious, firmware if the update mechanism lacks robust code-signing verification.\nSuccessful exploitation requires no prior authentication and relies on the attacker's ability to communicate with the device's MQTT broker service over the network.\nGiven that these devices are typically internet-facing or part of a home/office network, this issue presents a significant threat to the availability and integrity of the mesh ecosystem.",
  "technicalDetails": "The root cause of the vulnerability resides in the 'informSyncUpgfw' function, which serves as the handler for synchronization-based firmware upgrade commands within the device's firmware management logic.\nThe system architecture utilizes an MQTT message broker, specifically the 'cs_broker' component, to facilitate inter-node communication across the mesh network.\nAnalysis of the affected function reveals that it lacks sufficient access control checks for incoming MQTT packets, failing to verify whether the command originated from a legitimate administrative source or a trusted peer.\nThe attack flow proceeds as follows: First, an unauthenticated attacker identifies the accessible MQTT interface managed by 'cs_broker'. Second, the attacker constructs a malicious MQTT message designed to trigger the firmware update sequence, specifically targeting the logic handled by 'informSyncUpgfw'.\nThird, upon receiving and processing the crafted message, the 'cs_broker' component routes the command to 'informSyncUpgfw' without applying authentication tokens or source validation. Finally, the function interprets the command and executes the firmware update routine across connected mesh slave devices.\nThis behavior allows an attacker to gain indirect control over the update lifecycle of the mesh cluster. By forcing slave units into a firmware update state, an attacker can intentionally disrupt service availability or potentially downgrade the device to a version containing known vulnerabilities if the update mechanism does not properly enforce version rollback protections.\nBecause the 'cs_broker' component processes these messages globally within the mesh environment, a single packet sent to the broker can cause a cascade effect, triggering updates across multiple interconnected devices simultaneously. The lack of cryptographic signing or nonce verification within the MQTT payload exchange exacerbates this issue, as the device accepts the payload as a legitimate administrative command solely based on the message structure rather than the identity of the sender.\nThis flaw effectively bypasses the web interface and administrative login mechanisms, providing an unauthenticated execution path for sensitive maintenance functions."
}