A critical stack-based buffer overflow vulnerability in Tenda AC21 routers exposes devices to remote denial-of-service attacks and potential code execution.

The vulnerability exists in the fromSetIpMacBind function within the /bin/httpd binary, specifically triggered by the list parameter of the /goform/SetIpMacBind endpoint. Due to the use of strcpy without boundary checks, a specially crafted HTTP POST request exceeding 128 bytes can cause a stack buffer overflow, requiring low-privileged authentication.

Successful exploitation of this vulnerability allows an attacker to crash the router, resulting in a denial-of-service for all connected users and business operations relying on the network. With a CVSS score of 8.8, the high severity reflects the potential for remote exploitation and the critical nature of the affected networking hardware. Compromise of edge devices often serves as a primary entry point for deeper lateral movement within a corporate or home network.

Immediate Action: There is currently no official patch available from the vendor. Administrators should immediately restrict access to the router management interface to trusted internal segments or disable remote management until a firmware update is released.

Proactive Monitoring: Monitor network traffic for anomalous HTTP POST requests directed at the /goform/SetIpMacBind endpoint, particularly those containing excessively long strings in the list parameter.

Compensating Controls: Deploy a Web Application Firewall or an Intrusion Prevention System with custom rules to drop requests containing oversized parameters directed at the identified vulnerable endpoint.

Public Exploit Available: Yes, a published proof-of-concept exists, as documented in the research write-up provided by the Northwestern Polytechnical University School of Cybersecurity.

Given the high CVSS score and the public availability of exploit code, Tenda AC21 users must treat this vulnerability with high priority. Organizations should isolate the management interfaces of these routers from the public internet immediately to prevent remote exploitation. Monitor vendor communication channels closely for the release of a patched firmware version and apply it as soon as it becomes available.