CVE-2026-3679 identifies a stack-based buffer overflow vulnerability in the Tenda FH451 router firmware version 1.0.0.9. The vulnerability resides in the formQuickIndex function, specifically in the handling of the mit_linktype and PPPOEPassword parameters within the /goform/QuickIndex endpoint. By crafting malicious requests that manipulate these parameters, an attacker can overflow a stack buffer, potentially overwriting control data such as return addresses or function pointers. This can lead to arbitrary code execution or cause the device to crash, resulting in denial of service. The vulnerability is remotely exploitable without requiring authentication or user interaction, making it highly accessible to attackers scanning for vulnerable devices. The CVSS 4.0 vector indicates network attack vector (AV:N), low attack complexity (AC:L), no privileges required (PR:L), no user interaction (UI:N), and high impact on confidentiality, integrity, and availability (C:H, I:H, A:H). Although no active exploitation has been reported, a public exploit exists, increasing the likelihood of future attacks. The lack of available patches at the time of publication necessitates immediate mitigation efforts. This vulnerability highlights the risks associated with insecure input validation in embedded device web interfaces, which are common attack vectors in IoT and networking equipment.

The impact of CVE-2026-3679 is significant for organizations relying on Tenda FH451 routers. Successful exploitation can lead to full compromise of the affected device, allowing attackers to execute arbitrary code with elevated privileges. This can result in unauthorized access to internal networks, interception or manipulation of network traffic, and disruption of network services through denial of service. The confidentiality, integrity, and availability of organizational data and systems connected through these routers are at risk. Given the remote exploitability without authentication, attackers can scan and compromise vulnerable devices en masse, potentially using them as footholds for lateral movement or as part of botnets for broader attacks. The vulnerability poses a particular threat to small and medium enterprises, ISPs, and home users who may not have robust network defenses or timely patch management. Additionally, compromised routers can be leveraged to bypass network security controls, undermining overall organizational security posture.

To mitigate CVE-2026-3679, organizations should immediately restrict remote access to the Tenda FH451 management interface by disabling WAN-side administration and limiting access to trusted internal networks only. Network segmentation should be employed to isolate vulnerable devices from critical infrastructure. Monitoring network traffic for unusual requests targeting /goform/QuickIndex or abnormal authentication attempts can help detect exploitation attempts. If possible, upgrade the router firmware to a version that addresses this vulnerability once released by the vendor. In the absence of an official patch, consider deploying web application firewalls or intrusion prevention systems with custom signatures to block exploit attempts. Regularly audit and update router configurations to disable unused services and enforce strong authentication mechanisms. Additionally, organizations should maintain an inventory of affected devices and plan for their replacement if vendor support is discontinued. Educating users about the risks of exposed network devices and encouraging secure configuration practices will further reduce exposure.