CVE-2026-3677 is a stack-based buffer overflow vulnerability identified in the Tenda FH451 router firmware version 1.0.0.9. The flaw resides in the fromSetCfm function within the /goform/setcfm endpoint, which processes HTTP requests containing the parameters funcname and funcpara1. Improper validation or bounds checking on these parameters allows an attacker to overflow the stack buffer, potentially overwriting the return address or other control data. This can enable remote attackers to execute arbitrary code with elevated privileges on the device. The vulnerability is remotely exploitable without requiring authentication or user interaction, increasing its risk profile. The CVSS v4.0 score is 8.7 (high), reflecting the ease of exploitation and the severe impact on confidentiality, integrity, and availability. While no confirmed exploits in the wild have been reported, a public exploit exists, indicating that attackers could weaponize this vulnerability. The lack of available patches at the time of disclosure necessitates immediate mitigation efforts. Given the critical role of routers in network infrastructure, exploitation could lead to network compromise, data interception, or persistent footholds for attackers.

The impact of CVE-2026-3677 is significant for organizations using Tenda FH451 routers, as successful exploitation can lead to full device compromise. Attackers could execute arbitrary code remotely, potentially gaining control over network traffic, intercepting sensitive data, or launching further attacks within the network. This threatens confidentiality by exposing data, integrity by allowing unauthorized changes to device configuration or firmware, and availability by causing device crashes or denial of service. The vulnerability's remote and unauthenticated nature increases the attack surface, making it feasible for widespread exploitation, especially in environments where these routers are exposed to untrusted networks. Organizations relying on these devices for critical connectivity or security functions face risks of operational disruption and data breaches. Additionally, compromised routers could be leveraged as part of botnets or for lateral movement within enterprise networks.

1. Immediately restrict remote access to the router’s management interface by disabling WAN-side access or implementing strict firewall rules to limit access to trusted IP addresses. 2. Monitor network traffic for unusual requests targeting the /goform/setcfm endpoint, especially those containing suspicious funcname or funcpara1 parameters. 3. If possible, upgrade the router firmware to a version that addresses this vulnerability once released by Tenda. 4. In the absence of patches, consider deploying network-level protections such as Web Application Firewalls (WAFs) or Intrusion Prevention Systems (IPS) configured to detect and block exploit attempts targeting this vulnerability. 5. Conduct regular security audits of network devices to identify and isolate vulnerable hardware. 6. Educate network administrators about this vulnerability and ensure incident response plans include steps for potential exploitation scenarios. 7. Where feasible, replace affected devices with models from vendors with timely security update practices.