CVE-2025-8940 is a high-severity buffer overflow vulnerability affecting the Tenda AC20 router firmware versions up to 16.03.08.12. The vulnerability exists in the strcpy function within the /goform/saveParentControlInfo endpoint, which processes the 'Time' argument. Because strcpy does not perform bounds checking, an attacker can supply a specially crafted input to overflow the buffer, leading to memory corruption. This flaw can be exploited remotely without user interaction or 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, allowing potential arbitrary code execution or denial of service. Although no public exploits are currently known in the wild, the exploit code has been disclosed publicly, increasing the risk of exploitation. The vulnerability is critical for devices exposed to untrusted networks, especially those with remote management interfaces enabled. The lack of patch links suggests that a vendor fix may not yet be available, emphasizing the need for mitigation through configuration and network controls.

For European organizations, this vulnerability poses a significant risk, particularly for enterprises and service providers using Tenda AC20 routers in their network infrastructure. Exploitation could allow attackers to execute arbitrary code remotely, potentially leading to full device compromise, network infiltration, data interception, or disruption of network services. This is especially critical for organizations relying on these routers for perimeter security or remote access. Given the router's role in home and small office environments, widespread exploitation could also impact remote workers and small businesses, increasing the attack surface. The vulnerability could facilitate lateral movement within corporate networks or serve as a foothold for further attacks. Additionally, critical infrastructure sectors using these devices may face operational disruptions or data breaches, affecting compliance with European data protection regulations such as GDPR.

1. Immediately identify and inventory all Tenda AC20 devices within the network and verify firmware versions. 2. Disable remote management interfaces or restrict access to trusted IP addresses only, minimizing exposure to untrusted networks. 3. Implement network segmentation to isolate vulnerable devices from critical assets. 4. Monitor network traffic for anomalous requests targeting /goform/saveParentControlInfo or unusual payload sizes indicative of buffer overflow attempts. 5. Apply strict input validation and filtering at network perimeter devices, if possible, to block malformed requests. 6. Engage with Tenda support to obtain official patches or firmware updates addressing this vulnerability and plan prompt deployment once available. 7. Consider replacing vulnerable devices if patches are unavailable or delayed, especially in high-risk environments. 8. Educate IT staff about this vulnerability and ensure incident response plans include detection and containment measures for exploitation attempts.