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, where improper handling of the input parameters funcname and funcpara1 allows an attacker to overflow the stack buffer. This vulnerability can be triggered remotely over the network without requiring authentication or user interaction, making it highly exploitable. The overflow can lead to arbitrary code execution with elevated privileges, potentially allowing attackers to take full control of the device. The vulnerability has a CVSS 4.0 base score of 8.7, indicating high severity, with network attack vector, low attack complexity, no privileges or user interaction needed, and high impact on confidentiality, integrity, and availability. Although no confirmed exploits are currently active in the wild, the public availability of exploit code increases the likelihood of attacks. The affected product, Tenda FH451, is a consumer and small office router, commonly deployed in various regions, particularly in Asia and emerging markets. The vulnerability poses significant risks including device takeover, network compromise, and lateral movement within affected networks. No official patches or mitigation links have been provided yet, emphasizing the need for immediate risk management and defensive measures.

The impact of CVE-2026-3677 is substantial for organizations and individuals using the Tenda FH451 router version 1.0.0.9. Successful exploitation can lead to complete device compromise, allowing attackers to execute arbitrary code with elevated privileges. This can result in unauthorized access to internal networks, interception or manipulation of network traffic, disruption of network services, and potential pivoting to other connected systems. The confidentiality of sensitive data passing through the router can be breached, integrity of network communications compromised, and availability of network services disrupted. Given the router’s role as a gateway device, exploitation can severely undermine network security posture. The remote, unauthenticated nature of the vulnerability increases the attack surface and risk, especially for organizations with exposed or poorly segmented networks. The lack of patches or official mitigations further exacerbates the threat, potentially leading to widespread exploitation if attackers leverage the public exploit code.

1. Immediate mitigation should include isolating affected Tenda FH451 devices from untrusted networks, especially the internet, to reduce exposure. 2. Network administrators should implement strict firewall rules to restrict access to the /goform/setcfm endpoint, blocking unauthorized inbound traffic. 3. Employ network segmentation to limit the impact of a compromised router and prevent lateral movement. 4. Monitor network traffic for unusual activity indicative of exploitation attempts, such as malformed requests targeting /goform/setcfm. 5. Use intrusion detection and prevention systems (IDS/IPS) with updated signatures to detect exploitation attempts. 6. Contact Tenda support or monitor official channels for firmware updates or patches addressing this vulnerability and apply them promptly once available. 7. Consider replacing affected devices with models from vendors with a stronger security track record if patches are delayed. 8. Educate users and administrators about the risks and signs of compromise related to this vulnerability. 9. Regularly audit and update device configurations to minimize attack surface and disable unnecessary services or endpoints. 10. Implement strong network access controls and authentication mechanisms to reduce risk from other potential vulnerabilities.