CVE-2025-5609 is a critical buffer overflow vulnerability identified in the Tenda AC18 router, specifically in firmware version 15.03.05.05. The flaw exists in the function fromadvsetlanip within the /goform/AdvSetLanip endpoint. The vulnerability arises due to improper handling of the lanMask argument, which can be manipulated by an attacker to overflow a buffer. This overflow can lead to arbitrary code execution or cause the device to crash, potentially resulting in denial of service. The vulnerability is remotely exploitable without requiring user interaction or prior authentication, making it highly dangerous. The CVSS 4.0 score of 8.7 reflects a high severity, with network attack vector, low attack complexity, no privileges or user interaction needed, and high impact on confidentiality, integrity, and availability. Although no public exploits have been observed in the wild yet, the exploit code has been disclosed publicly, increasing the risk of imminent attacks. The lack of an official patch or mitigation from the vendor at the time of publication further exacerbates the threat. This vulnerability could allow attackers to take full control of affected routers, intercept or manipulate network traffic, and pivot into internal networks, posing significant risks to network security and data privacy.

For European organizations, the impact of this vulnerability can be substantial. Tenda AC18 routers are commonly used in small to medium-sized enterprises and home office environments, which are prevalent across Europe. Exploitation could lead to unauthorized access to internal networks, data breaches, and disruption of business operations due to denial of service. Confidentiality is at risk as attackers could intercept sensitive communications; integrity could be compromised by injecting malicious traffic or altering configurations; availability could be affected by causing router crashes or network outages. Given the remote and unauthenticated nature of the exploit, attackers could target vulnerable routers en masse, potentially impacting critical infrastructure, corporate networks, and residential users. This could also facilitate lateral movement within corporate networks, increasing the scope of compromise. The public disclosure of exploit code raises the urgency for European organizations to assess and remediate affected devices promptly to prevent exploitation.

Immediate mitigation steps include isolating affected Tenda AC18 routers from critical network segments and the internet until a patch is available. Network administrators should implement strict firewall rules to restrict access to the /goform/AdvSetLanip endpoint, ideally blocking unsolicited inbound traffic to the router’s management interfaces. Monitoring network traffic for unusual patterns or attempts to access this endpoint can help detect exploitation attempts. Organizations should inventory their network devices to identify all Tenda AC18 routers running the vulnerable firmware version 15.03.05.05. If possible, downgrade or replace affected devices with models not vulnerable to this issue. Applying vendor firmware updates is the definitive fix once released; until then, consider deploying network segmentation and intrusion detection/prevention systems to limit exposure. Additionally, educating users about the risks and encouraging secure router configurations (e.g., disabling remote management if not needed) can reduce attack surface. Regular backups of router configurations and network data will aid recovery if an attack occurs.