A stack-based buffer overflow vulnerability in the Tenda FH1202 router, identified as CVE-2026-3808, allows remote authenticated attackers to achieve code execution or system crashes.

The vulnerability resides within the formWebTypeLibrary function in the /goform/webtypelibrary endpoint. An authenticated attacker can trigger a stack-based buffer overflow by providing an excessively long string to the webSiteId argument, which is processed by the strcat function without adequate length validation.

Successful exploitation of this vulnerability poses a severe risk to network integrity and availability. An attacker gaining remote code execution on a network device can intercept traffic, pivot into internal segments, or render the device unresponsive, leading to significant operational downtime. Given the high CVSS score of 8.8, this flaw represents a critical security failure that could compromise the entire local network environment.

Immediate Action: There is currently no official patch available from the vendor. Administrators should immediately restrict access to the web management interface to trusted IP addresses only or disable remote management entirely.

Proactive Monitoring: Monitor device access logs for unusual POST requests directed at the /goform/webtypelibrary endpoint, particularly those containing abnormally long payloads in the webSiteId parameter.

Compensating Controls: If the device supports it, implement strict network segmentation to isolate the management interface from the internal network and external internet access.

Public Exploit Available: Yes, a functional proof-of-concept is available via the researcher's GitHub repository.

The severity of this vulnerability necessitates immediate administrative intervention. Because no vendor patch is currently available, organizations must treat the affected Tenda FH1202 devices as high-risk assets. Restricting management access and monitoring for malicious traffic patterns are the only viable defenses until the manufacturer releases a firmware update addressing the buffer overflow.