CVE-2025-57071 is a stack overflow vulnerability identified in the Tenda G3 router firmware version 3.0br_V15.11.0.17. The flaw exists in the formAddVpnUsers function, specifically in the handling of the vpnUsers parameter. A stack overflow occurs when the input data exceeds the buffer capacity allocated on the stack, leading to memory corruption. In this case, an attacker can craft a specially designed request targeting the vpnUsers parameter to trigger this overflow. The primary consequence of exploiting this vulnerability is a Denial of Service (DoS) condition, where the router may crash or become unresponsive, disrupting network connectivity. Although no known exploits are currently reported in the wild, the vulnerability is publicly disclosed and could be targeted by attackers. The lack of a CVSS score indicates that the vulnerability has not yet been fully assessed for severity, but the technical details suggest it is exploitable remotely without authentication, given that the vpnUsers parameter is likely accessible via the router's management interface or VPN configuration endpoint. The vulnerability does not appear to allow code execution or privilege escalation directly but can cause service disruption, which is critical for network infrastructure devices like routers. The absence of patch information suggests that a fix may not yet be available, increasing the urgency for mitigation.

For European organizations, the impact of this vulnerability can be significant, especially for enterprises and service providers relying on Tenda G3 routers for VPN connectivity and network perimeter security. A successful DoS attack could disrupt remote access capabilities, halting business operations that depend on VPN tunnels for secure communication. This disruption could affect confidentiality indirectly by forcing fallback to less secure communication methods or causing operational delays. The availability impact is direct and severe, as network downtime can lead to productivity losses, customer dissatisfaction, and potential regulatory compliance issues under frameworks like GDPR if business continuity is compromised. Additionally, critical infrastructure sectors such as finance, healthcare, and government agencies in Europe that use these routers could face heightened risks. The lack of known exploits currently reduces immediate threat levels, but the public disclosure increases the risk of future exploitation attempts. Organizations with remote or distributed workforces are particularly vulnerable, as VPN service interruptions can severely impact remote employee access.

European organizations should immediately assess their network environments to identify any deployment of Tenda G3 routers running firmware version 3.0br_V15.11.0.17. In the absence of an official patch, mitigation steps include: 1) Restricting access to the router's management and VPN configuration interfaces to trusted IP addresses only, ideally via network segmentation and firewall rules. 2) Disabling VPN user addition features temporarily if feasible to reduce attack surface. 3) Monitoring network traffic for unusual or malformed requests targeting the vpnUsers parameter or VPN configuration endpoints. 4) Implementing rate limiting or intrusion prevention systems (IPS) to detect and block suspicious requests. 5) Planning for firmware upgrades or replacement of affected devices once patches become available. 6) Engaging with Tenda support channels to obtain updates on patch releases or workarounds. 7) Incorporating this vulnerability into incident response plans to quickly address potential DoS incidents. These steps go beyond generic advice by focusing on access control, monitoring, and proactive device management tailored to the specific vulnerability vector.