CVE-2025-65220 identifies a buffer overflow vulnerability in the Tenda AC21 router firmware version V16.03.08.16. The flaw exists in the /goform/SetVirtualServerCfg endpoint, specifically in the handling of the 'list' parameter. Buffer overflow vulnerabilities occur when input data exceeds the allocated buffer size, potentially overwriting adjacent memory. This can lead to unpredictable behavior including crashes, reboots, or in some cases, arbitrary code execution. However, this particular vulnerability has a CVSS score of 4.3 (medium) with the vector indicating that the attack vector is adjacent network (AV:A), meaning the attacker must have access to the same local or adjacent network segment. No privileges are required (PR:N), no user interaction is needed (UI:N), and the impact is limited to availability (A:L) with no confidentiality or integrity impact. The vulnerability is categorized under CWE-121 (Stack-based Buffer Overflow). There are currently no known exploits in the wild and no patches have been published. The lack of authentication requirement means that an attacker on the local network could send crafted requests to the vulnerable endpoint to trigger the overflow, potentially causing denial of service by crashing the router or causing it to reboot. The absence of known exploits and patches suggests this is a newly disclosed vulnerability requiring attention from network administrators using this device. Given the nature of the vulnerability, exploitation is limited to attackers with local network access, reducing the risk from remote internet-based attackers unless the device management interface is exposed externally.

For European organizations, the primary impact of CVE-2025-65220 is on availability. A successful exploit could cause Tenda AC21 routers to crash or reboot, leading to network downtime and disruption of internet connectivity. This can affect both home users and small businesses relying on these routers for critical connectivity. While the vulnerability does not compromise confidentiality or integrity, denial of service conditions can interrupt business operations, remote work, and access to cloud services. Organizations with remote or hybrid workforces may experience productivity losses if affected routers are used in home offices. Additionally, if the router is part of a larger network infrastructure, repeated crashes could complicate network management and incident response. The requirement for adjacent network access limits exploitation to attackers who have gained some level of internal network presence, such as malicious insiders or compromised devices within the local network. This reduces the risk of wide-scale remote exploitation but highlights the importance of internal network security controls. The lack of known exploits in the wild currently reduces immediate risk but does not preclude future exploitation attempts once details become more widely known.

1. Network Segmentation: Isolate router management interfaces from general user networks to prevent unauthorized access from adjacent devices. 2. Access Control: Restrict access to the router’s management interface to trusted IP addresses or VLANs. 3. Disable Remote Management: Ensure that remote management over WAN is disabled unless absolutely necessary and secured via VPN or other strong authentication methods. 4. Monitor Network Traffic: Implement monitoring to detect unusual or malformed requests targeting /goform/SetVirtualServerCfg or other router endpoints. 5. Firmware Updates: Regularly check for firmware updates from Tenda and apply patches promptly once available. 6. Device Replacement: Consider replacing Tenda AC21 routers with devices from vendors with more robust security update policies if patching is delayed. 7. Incident Response: Prepare to respond to potential denial of service incidents by having backup connectivity options and procedures for rapid device reboot or replacement. 8. User Awareness: Educate users about the risks of connecting untrusted devices to the local network that could be used to exploit this vulnerability.