The vulnerability identified as CVE-2025-65226 affects the Tenda AC21 router running firmware version V16.03.08.16. It is a buffer overflow vulnerability triggered via the deviceId parameter in the /goform/saveParentControlInfo HTTP endpoint. Buffer overflow vulnerabilities occur when input data exceeds the allocated buffer size, overwriting adjacent memory and potentially allowing attackers to execute arbitrary code or crash the device. In this case, the deviceId parameter is insufficiently validated or sanitized, enabling crafted requests to overflow the buffer. Since this endpoint is part of the router's web interface, it is likely accessible to attackers on the local network or possibly remotely if remote management is enabled. No authentication requirements are specified, which implies that exploitation could be performed without credentials, increasing the attack surface. The vulnerability has been published recently with no CVSS score assigned and no known exploits in the wild yet. The absence of patches or mitigation details from the vendor means that affected users remain exposed. Given the nature of the vulnerability and the device's role as a network gateway, successful exploitation could lead to full compromise of the router, allowing attackers to intercept, modify, or disrupt network traffic, and potentially pivot to internal networks. The Tenda AC21 router is a popular consumer and small business device, making this vulnerability relevant to a broad user base.

For European organizations, the impact of this vulnerability can be significant, especially for small and medium enterprises (SMEs) and home office users relying on Tenda AC21 routers. Compromise of the router could lead to interception of sensitive communications, insertion of malicious payloads into network traffic, and disruption of internet connectivity. This could result in data breaches, loss of confidentiality, and operational downtime. Furthermore, attackers gaining control over the router could use it as a foothold to launch further attacks against internal systems or as part of a botnet for broader malicious campaigns. The lack of authentication for exploitation increases the risk of remote attacks, particularly if remote management features are enabled or if the device is exposed to the internet. Given the widespread use of Tenda routers in Europe, the vulnerability could affect a large number of endpoints, amplifying the potential impact on regional cybersecurity posture.

1. Immediately disable remote management features on Tenda AC21 routers to reduce exposure to external attackers. 2. Restrict access to the router's web interface to trusted internal networks only, using firewall rules or network segmentation. 3. Monitor network traffic for unusual or malformed requests targeting the /goform/saveParentControlInfo endpoint, which could indicate exploitation attempts. 4. Apply strict input validation and filtering at network perimeters to detect and block suspicious payloads targeting the deviceId parameter. 5. Regularly check for firmware updates from Tenda and apply patches promptly once available. 6. Consider replacing vulnerable routers with models from vendors with a strong security track record if patches are delayed. 7. Educate users about the risks of exposing router management interfaces and encourage secure configuration practices. 8. Implement network intrusion detection systems capable of identifying buffer overflow attack patterns targeting embedded devices.