CVE-2025-8940 is a high-severity buffer overflow vulnerability affecting the Tenda AC20 router firmware versions up to 16.03.08.12. The flaw exists in the strcpy function within the /goform/saveParentControlInfo endpoint, specifically when processing the 'Time' argument. Because strcpy does not perform bounds checking, an attacker can supply a crafted input that exceeds the buffer size, causing a buffer overflow. This vulnerability can be exploited remotely without 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 at a high level, potentially allowing 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 active exploitation. The vulnerability does not require user interaction but does require low privileges (PR:L), which may correspond to an authenticated session or a low-level access vector. The absence of a patch link suggests that a fix may not yet be publicly available, increasing the urgency for mitigation. The Tenda AC20 is a widely used consumer and small office router, making this vulnerability relevant for environments relying on this device for network connectivity and security.

For European organizations, the exploitation of CVE-2025-8940 could lead to significant network compromise. Successful exploitation could allow attackers to execute arbitrary code on the router, potentially gaining control over network traffic, intercepting sensitive data, or pivoting to internal systems. This threatens the confidentiality and integrity of organizational data and could disrupt availability by causing router crashes or network outages. Small and medium enterprises (SMEs) and home offices using Tenda AC20 devices are particularly at risk, as these routers are commonly deployed in such environments due to their cost-effectiveness. Compromise of these devices could facilitate broader attacks such as man-in-the-middle, data exfiltration, or lateral movement within corporate networks. Given the router’s role as a network gateway, the impact extends beyond the device itself to all connected systems, amplifying the potential damage. The lack of a patch and public exploit availability heighten the urgency for European organizations to address this vulnerability promptly.

European organizations should immediately inventory their network infrastructure to identify any Tenda AC20 devices running affected firmware versions (up to 16.03.08.12). Until an official patch is released, organizations should implement network-level mitigations such as restricting access to the router’s management interfaces to trusted IP addresses only, ideally via VPN or internal network segments. Disable remote management features if not required. Employ network intrusion detection/prevention systems (IDS/IPS) with signatures tuned to detect exploitation attempts targeting /goform/saveParentControlInfo or suspicious strcpy-related payloads. Regularly monitor router logs for anomalous activity. Where possible, replace vulnerable devices with models from vendors with timely security updates. Additionally, enforce strong network segmentation to limit the impact of a compromised router and maintain up-to-date backups of router configurations. Engage with Tenda support channels to obtain or request firmware updates addressing this vulnerability. Finally, educate IT staff about this vulnerability and the importance of rapid response to firmware updates.