CVE-2025-10815 is a high-severity buffer overflow vulnerability affecting the Tenda AC20 router firmware versions up to 16.03.08.12. The vulnerability resides in the HTTP POST request handler component, specifically in the /goform/SetPptpServerCfg function. This function uses the unsafe strcpy function to copy the startIp parameter without proper bounds checking, which allows an attacker to overflow the buffer by sending a specially crafted HTTP POST request. The overflow can corrupt adjacent memory, potentially leading to arbitrary code execution or denial of service. The vulnerability is remotely exploitable without authentication or user interaction, making it highly dangerous. The CVSS 4.0 score is 8.7, reflecting the ease of exploitation (network attack vector, low complexity), no privileges or user interaction required, and high impact on confidentiality, integrity, and availability. Although no known exploits are currently observed in the wild, a public exploit is available, increasing the risk of active exploitation. The vulnerability affects a widely deployed consumer and small office router model, which is often used as a gateway device, making it a critical point of compromise in network infrastructure. Attackers exploiting this flaw could gain control over the router, intercept or manipulate traffic, pivot into internal networks, or disrupt network connectivity.

For European organizations, the impact of this vulnerability can be significant. Many small and medium enterprises (SMEs) and residential users rely on Tenda AC20 routers for internet connectivity. Compromise of these devices could lead to unauthorized access to internal networks, interception of sensitive communications, and potential lateral movement to other critical systems. This is particularly concerning for organizations with remote or hybrid work setups where such routers are used as primary network gateways. The loss of confidentiality could expose personal or corporate data, while integrity and availability impacts could disrupt business operations. Additionally, compromised routers could be leveraged as part of botnets or for launching further attacks, amplifying the threat landscape. Given the remote exploitability and lack of required authentication, attackers can target vulnerable devices en masse, increasing the risk of widespread disruption across European networks.

1. Immediate firmware upgrade: Organizations and users should update the Tenda AC20 firmware to a version later than 16.03.08.12 once the vendor releases a patch addressing this vulnerability. 2. Network segmentation: Isolate vulnerable routers from critical internal networks to limit potential lateral movement in case of compromise. 3. Disable PPTP server functionality if not required, as the vulnerable endpoint is related to PPTP server configuration. 4. Implement network-level protections such as firewall rules to restrict access to the router’s management interface from untrusted networks, especially blocking WAN-side HTTP POST requests to /goform/SetPptpServerCfg. 5. Monitor network traffic for unusual POST requests targeting the router’s management interface and signs of exploitation attempts. 6. Replace legacy or unsupported devices with routers from vendors with strong security update policies to reduce future risk. 7. Educate users and administrators about the risks of using default or outdated firmware and encourage regular updates and security hygiene.