A critical stack-based buffer overflow vulnerability in the Tenda AC20 router allows remote attackers to trigger memory corruption and potential code execution.

The vulnerability exists in the /goform/SetFirewallCfg function, where the strcpy operation fails to perform bounds checking on the firewallEn parameter. An authenticated attacker can submit an oversized string to this parameter, resulting in a stack-based buffer overflow.

The exploitation of this vulnerability can lead to a complete compromise of the affected network device, including denial of service or remote code execution. With a CVSS score of 8.8, this flaw represents a high risk to organizational infrastructure, as attackers gaining control over core routing equipment can intercept traffic, pivot into internal segments, or disrupt business operations.

Immediate Action: Since no official patch is currently identified, administrators should restrict management access to the device to trusted internal networks only and disable remote administration features if they are not strictly required.

Proactive Monitoring: Monitor firewall and web logs for anomalous POST requests directed at the /goform/SetFirewallCfg endpoint, specifically looking for unusually long string payloads.

Compensating Controls: Implement a Web Application Firewall (WAF) or an intrusion prevention system (IPS) rule to inspect and block traffic containing oversized input in the firewallEn parameter.

Public Exploit Available: Yes, a published proof-of-concept exists, as documented in the referenced GitHub research repository.

Given the availability of a public proof-of-concept and the critical nature of the impact, organizations utilizing the Tenda AC20 router must prioritize the mitigation of this vulnerability. As no vendor patch is confirmed, enforcing strict network segmentation and limiting access to the device management interface is essential to reduce the attack surface until the vendor releases a secure firmware update.