The vulnerability identified as CVE-2025-65220 affects the Tenda AC21 router running firmware version V16.03.08.16. It is a buffer overflow issue located in the /goform/SetVirtualServerCfg endpoint, specifically triggered via the 'list' parameter. Buffer overflow vulnerabilities occur when input data exceeds the allocated buffer size, potentially overwriting adjacent memory and allowing attackers to execute arbitrary code or crash the system. In this case, an attacker can send a specially crafted HTTP request to the router's web management interface targeting the vulnerable endpoint to exploit the flaw. Since the vulnerability is in a web form handler, it is likely exploitable remotely without authentication, increasing the attack surface. No CVSS score has been assigned yet, and no known exploits have been reported in the wild, but the vulnerability is publicly disclosed and published in the CVE database. The Tenda AC21 is a popular dual-band Wi-Fi 6 router used in home and small office environments, including in Europe. Exploitation could lead to full compromise of the router, enabling attackers to intercept, modify, or disrupt network traffic, launch further attacks on internal networks, or create persistent backdoors. The absence of patches or mitigation details at this time necessitates proactive defensive measures. The vulnerability's technical details indicate a high-risk scenario due to the potential for remote code execution without authentication and the critical role routers play in network security.

For European organizations, especially small and medium enterprises (SMEs) and home offices using Tenda AC21 routers, this vulnerability poses significant risks. Successful exploitation could lead to unauthorized access to internal networks, interception of sensitive data, disruption of internet connectivity, and potential lateral movement within corporate networks. Confidentiality is at risk as attackers could capture unencrypted traffic or manipulate DNS settings. Integrity could be compromised by altering network configurations or injecting malicious payloads. Availability could be affected by causing router crashes or denial of service conditions. The lack of authentication requirement means attackers can exploit the vulnerability remotely if the router's management interface is exposed to the internet or accessible from compromised internal devices. This threat is particularly concerning in countries with high adoption rates of Tenda routers and where remote work has increased reliance on home networking equipment. The impact extends beyond individual users to organizational security posture, potentially affecting business continuity and data protection compliance obligations under GDPR.

Until an official patch is released by Tenda, European organizations should implement several specific mitigation steps: 1) Immediately restrict access to the router's web management interface by disabling remote management features or limiting access to trusted IP addresses only. 2) Change default credentials to strong, unique passwords to reduce the risk of unauthorized access. 3) Monitor network traffic for unusual requests targeting the /goform/SetVirtualServerCfg endpoint or anomalous HTTP POST requests that could indicate exploitation attempts. 4) Segment networks to isolate critical systems from devices using vulnerable routers, minimizing lateral movement opportunities. 5) Educate users about the risks of exposing router management interfaces and encourage regular firmware update checks. 6) Engage with Tenda support channels to obtain information on forthcoming patches and apply updates promptly once available. 7) Consider deploying network intrusion detection/prevention systems (IDS/IPS) with signatures targeting this vulnerability once they become available. These measures go beyond generic advice by focusing on access control, monitoring, and network segmentation tailored to the specific vulnerability vector.