CVE-2026-3679 is a stack-based buffer overflow vulnerability identified in the Tenda FH451 router firmware version 1.0.0.9. The flaw resides in the formQuickIndex function, specifically in the handling of the mit_linktype and PPPOEPassword parameters submitted to the /goform/QuickIndex endpoint. Improper validation or bounds checking of these parameters allows an attacker to overflow the stack buffer, potentially overwriting the return address or other control data. This can lead to arbitrary code execution or cause the device to crash, resulting in denial of service. The vulnerability is remotely exploitable over the network without requiring authentication or user interaction, making it highly accessible to attackers. The CVSS v4.0 score of 8.7 reflects the high impact on confidentiality, integrity, and availability, combined with low attack complexity and no privileges required. Although no active exploitation has been reported, a public exploit exists, increasing the likelihood of future attacks. The affected product, Tenda FH451, is a consumer-grade router widely used in various regions, making this vulnerability a significant threat to home and small office networks. The lack of an official patch at the time of publication necessitates immediate mitigation efforts to reduce exposure.

The vulnerability allows remote attackers to execute arbitrary code or cause denial of service on affected Tenda FH451 routers. Successful exploitation can compromise the confidentiality of network traffic, integrity of device configurations, and availability of network services. This can lead to unauthorized network access, interception or manipulation of data, and disruption of internet connectivity. For organizations relying on these routers for critical connectivity, this could result in operational downtime, data breaches, or serve as a foothold for further network intrusion. The ease of exploitation and absence of required authentication significantly increase the risk, especially in environments where these devices are directly exposed to the internet. The presence of a public exploit further elevates the threat level, potentially enabling widespread attacks. The impact extends beyond individual users to ISPs and enterprises that deploy these devices at scale, potentially affecting large user bases and critical infrastructure.

1. Immediately isolate affected Tenda FH451 devices from untrusted networks to prevent remote exploitation. 2. Monitor vendor communications closely for official firmware updates or patches addressing CVE-2026-3679 and apply them promptly upon release. 3. If patching is not yet available, implement network-level protections such as firewall rules to block access to the /goform/QuickIndex endpoint or restrict management interfaces to trusted internal networks only. 4. Employ intrusion detection/prevention systems (IDS/IPS) with signatures tuned to detect exploitation attempts targeting this vulnerability. 5. Change default credentials and disable remote management features if not required to reduce attack surface. 6. Conduct network segmentation to limit the exposure of vulnerable devices. 7. Regularly audit router configurations and logs for signs of compromise or anomalous activity. 8. Educate users on the risks of using outdated firmware and encourage timely updates. 9. Consider replacing affected devices with models from vendors with stronger security track records if timely patching is not feasible.