CVE-2025-8939 is a high-severity buffer overflow vulnerability affecting the Tenda AC20 router firmware versions up to 16.03.08.12. The vulnerability resides in an unspecified function within the /goform/WifiGuestSet endpoint, where manipulation of the 'shareSpeed' argument can trigger a buffer overflow condition. This flaw allows an attacker to remotely exploit the device without requiring user interaction or prior authentication, as indicated by the CVSS vector (AV:N/AC:L/AT:N/UI:N/PR:L). The vulnerability impacts confidentiality, integrity, and availability with high impact, potentially enabling remote code execution or denial of service. Although no known exploits are currently observed in the wild, the public disclosure of the exploit code increases the risk of imminent attacks. The vulnerability affects multiple firmware versions, indicating a broad attack surface for devices running these versions. The lack of available patches at the time of disclosure further exacerbates the risk, necessitating immediate mitigation efforts.

For European organizations, the exploitation of this vulnerability could lead to significant security breaches. Compromised Tenda AC20 routers could serve as entry points into corporate or home networks, allowing attackers to intercept sensitive data, disrupt network availability, or pivot to other internal systems. Given the router’s role in managing guest Wi-Fi access, attackers might also leverage this to bypass network segmentation controls. The potential for remote code execution means attackers could install persistent malware or create botnets, impacting operational continuity. Organizations relying on Tenda AC20 devices for network connectivity, especially in SMEs or home office environments, may face elevated risks. The disruption could affect data privacy compliance obligations under GDPR if personal data is exposed or network integrity is compromised.

Organizations should immediately inventory their network to identify Tenda AC20 devices running affected firmware versions. Until official patches are released, it is critical to restrict remote access to the router’s management interfaces, especially the /goform/WifiGuestSet endpoint. Network segmentation should be enforced to isolate guest Wi-Fi networks from sensitive internal resources. Employing network intrusion detection systems (NIDS) to monitor for anomalous traffic patterns targeting the vulnerable endpoint can provide early warning. Firmware updates should be applied promptly once available from Tenda. Additionally, consider replacing affected devices with models from vendors with more robust security update policies if timely patches are not forthcoming. Implementing strict firewall rules to block unsolicited inbound traffic to router management ports can further reduce exposure.