CVE-2025-65226 identifies a buffer overflow vulnerability in the Tenda AC21 router firmware version V16.03.08.16. The vulnerability is triggered via the deviceId parameter in the /goform/saveParentControlInfo HTTP endpoint. Buffer overflow (CWE-120) occurs when the input data exceeds the allocated buffer size, potentially overwriting adjacent memory. This can lead to denial of service conditions such as device crashes or reboots, impacting the router's availability. The vulnerability is remotely exploitable over the network with an attack vector classified as adjacent network (AV:A), meaning the attacker must be on the same local network or connected via VPN but does not require privileges or user interaction. The CVSS v3.1 score is 4.3 (medium), reflecting low impact on confidentiality and integrity but some impact on availability. No known exploits have been reported in the wild, and no patches or firmware updates have been published at this time. The lack of authentication requirements increases the risk in environments where the router management interface is exposed or accessible by untrusted users. The vulnerability affects a widely deployed consumer router model, which is often used in small offices and home environments, potentially serving as a pivot point for further network attacks if exploited.

For European organizations, exploitation of this vulnerability could result in denial of service on affected Tenda AC21 routers, causing network outages or intermittent connectivity loss. This disruption can impact business operations, especially for small and medium enterprises relying on these routers for internet access or internal network segmentation. While the vulnerability does not directly compromise data confidentiality or integrity, the loss of availability can degrade productivity and may open secondary attack vectors if attackers use the router as a foothold. Organizations with remote or hybrid work setups that expose router management interfaces to wider networks are at increased risk. The absence of known exploits reduces immediate threat but does not eliminate the risk of future weaponization. The impact is more pronounced in environments where network redundancy is limited or where critical services depend on the affected devices.

1. Immediately restrict access to the router's management interface by limiting it to trusted internal networks only; disable remote management if not required. 2. Implement network segmentation to isolate routers from critical infrastructure and sensitive data systems. 3. Monitor network traffic and router logs for unusual requests to the /goform/saveParentControlInfo endpoint or unexpected device reboots. 4. Employ intrusion detection/prevention systems (IDS/IPS) capable of detecting buffer overflow attempts or anomalous HTTP requests targeting router management interfaces. 5. Regularly audit and update router firmware; although no patch is currently available, subscribe to vendor advisories for timely updates. 6. Consider replacing vulnerable devices with models from vendors with stronger security track records if patching is delayed. 7. Educate IT staff about this vulnerability to ensure rapid response if exploitation signs appear. 8. Use VPNs and strong authentication methods to secure remote access to network devices, reducing exposure to adjacent network attacks.