CVE-2025-10815 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 HTTP POST request handler component, specifically within the /goform/SetPptpServerCfg endpoint. The vulnerability arises due to unsafe use of the strcpy function when processing the 'startIp' argument, which allows an attacker to overflow the buffer by sending a specially crafted HTTP POST request. This buffer overflow can lead to arbitrary code execution or denial of service conditions on the affected device. The vulnerability is remotely exploitable without authentication or user interaction, increasing its risk profile. The CVSS 4.0 base score is 8.7, reflecting high impact on confidentiality, integrity, and availability, with low attack complexity and no privileges required. Although no known exploits are currently observed in the wild, a public exploit is available, making exploitation feasible. The vulnerability affects a widely deployed consumer and small office router model, which is commonly used to provide network connectivity and VPN services via PPTP. Successful exploitation could allow attackers to compromise network infrastructure, intercept or manipulate traffic, and pivot into internal networks.

For European organizations, this vulnerability poses significant risks, especially for small and medium enterprises (SMEs) and home offices that rely on Tenda AC20 routers for network connectivity and VPN access. Exploitation could lead to unauthorized access to internal networks, data exfiltration, disruption of network services, and potential lateral movement to other critical systems. Given the router's role in managing VPN configurations, attackers might manipulate VPN settings to intercept or redirect sensitive communications. The lack of authentication requirement and remote exploitability means attackers can target vulnerable devices exposed to the internet or accessible from less secure network segments. This could impact confidentiality of corporate data, integrity of network configurations, and availability of network services, potentially causing operational disruptions and compliance issues under GDPR and other regulations.

Organizations should immediately identify and inventory all Tenda AC20 devices running affected firmware versions. Since no official patches or updates are referenced, mitigation should include: 1) Disabling remote management interfaces exposed to the internet, especially HTTP POST endpoints related to VPN configuration. 2) Restricting access to router management interfaces via network segmentation and firewall rules to trusted IP addresses only. 3) Monitoring network traffic for unusual POST requests targeting /goform/SetPptpServerCfg and signs of buffer overflow exploitation attempts. 4) If possible, upgrading firmware to a fixed version once released by Tenda. 5) As a temporary measure, disabling PPTP VPN services on the router to reduce attack surface. 6) Employing network intrusion detection systems (NIDS) with signatures for this vulnerability’s exploit patterns. 7) Educating IT staff about the vulnerability and ensuring incident response plans include this threat. These steps go beyond generic advice by focusing on access control, monitoring, and configuration changes specific to the vulnerable component.