CVE-2025-5851 is a critical buffer overflow vulnerability affecting the Tenda AC15 router, specifically version 15.03.05.19_multi. The flaw resides in the HTTP POST request handler component, within the function fromadvsetlanip located in the /goform/AdvSetLanip endpoint. The vulnerability is triggered by manipulating the lanMask argument, which leads to a buffer overflow condition. This type of vulnerability can allow an attacker to overwrite memory, potentially enabling arbitrary code execution or causing a denial of service. The vulnerability is remotely exploitable without requiring user interaction or authentication, as indicated by the CVSS vector (AV:N/AC:L/AT:N/UI:N/PR:L). The CVSS score of 8.7 (high severity) reflects the significant risk posed by this issue, with high impact on confidentiality, integrity, and availability. Although no known exploits are currently observed in the wild, the public disclosure of the exploit code increases the likelihood of exploitation attempts. The vulnerability affects a widely used consumer-grade router model, which is often deployed in home and small office environments, making it a potential target for attackers seeking to compromise network infrastructure or pivot into internal networks.

For European organizations, the impact of this vulnerability can be substantial, especially for small and medium enterprises (SMEs) and home offices relying on Tenda AC15 routers for network connectivity. Successful exploitation could lead to unauthorized access to internal networks, data exfiltration, or disruption of network services. Given the router’s role as a gateway device, attackers could leverage this vulnerability to intercept or manipulate network traffic, deploy malware, or establish persistent footholds. This risk extends to critical infrastructure sectors if such routers are used in less-secured environments. The lack of authentication requirement and remote exploitability heightens the threat, potentially enabling widespread automated attacks. Additionally, the buffer overflow could be exploited to cause denial of service, impacting availability of network services. The public availability of exploit code further increases the urgency for mitigation in European contexts where data protection regulations (e.g., GDPR) impose strict requirements on network security and breach prevention.

1. Immediate mitigation should include isolating or segmenting affected Tenda AC15 routers from critical network segments to limit potential lateral movement in case of compromise. 2. Network administrators should monitor network traffic for unusual POST requests to the /goform/AdvSetLanip endpoint, particularly those containing abnormal lanMask parameters, using intrusion detection/prevention systems (IDS/IPS) with custom signatures. 3. Implement strict firewall rules to restrict inbound access to router management interfaces from untrusted networks, ideally limiting access to trusted IP ranges or VPN connections. 4. Since no official patch is currently available, organizations should consider replacing affected devices with updated models or alternative routers with confirmed security updates. 5. Regularly audit and update router firmware once vendor patches are released, and subscribe to vendor security advisories for timely updates. 6. Employ network segmentation and zero-trust principles to minimize the impact of potential router compromises. 7. Educate users and administrators about the risks of exposing router management interfaces to the internet and encourage secure configuration practices.