A critical buffer overflow vulnerability in Tenda F456 firmware version 1.0.0.5 presents a significant risk of remote code execution.

This is a stack-based buffer overflow occurring within the fromPPTPUserSetting function of the httpd component. By sending a crafted POST request to the /goform/PPTPUserSetting endpoint with an excessively long delno parameter, an authenticated attacker can trigger memory corruption to achieve remote code execution.

Successful exploitation of this vulnerability can lead to a complete compromise of the affected router, potentially granting an attacker persistent access to the network. Given the CVSS score of 8.8, the vulnerability is classified as High, reflecting the potential for total loss of system integrity and availability. This could result in unauthorized data interception, lateral movement within the network, or prolonged service outages for critical business operations.

Immediate Action: Since no official patch is currently available, administrators should restrict access to the router management interface to trusted internal segments only. Disable the PPTP feature if it is not strictly required for business operations to reduce the attack surface.

Proactive Monitoring: Review web access logs for unusual POST requests directed at /goform/PPTPUserSetting. Monitor device stability for unexpected crashes or reboots that may indicate automated exploitation attempts.

Compensating Controls: Implement a Web Application Firewall (WAF) or network-based Intrusion Prevention System (IPS) rule to inspect and block excessively long input strings sent to the identified vulnerable endpoint.

Public Exploit Available: Yes, a functional proof-of-concept is documented in the research write-up by Li Tengzheng.

The severity of this flaw and the public availability of exploit material necessitate immediate attention. Organizations utilizing Tenda F456 devices should prioritize network segmentation and the restriction of management access until the manufacturer releases a firmware update that addresses this buffer overflow.