CVE-2025-3990 is a critical buffer overflow vulnerability identified in the TOTOLINK N150RT router, specifically affecting firmware version 3.4.0-B20190525. The vulnerability resides in an unspecified functionality related to the /boafrm/formVlan endpoint, where manipulation of the 'submit-url' argument can trigger a buffer overflow condition. This flaw allows an attacker to remotely exploit the device without requiring user interaction or prior authentication, as indicated by the CVSS vector (AV:N/AC:L/AT:N/UI:N/PR:L). The vulnerability impacts confidentiality, integrity, and availability at a high level, suggesting that successful exploitation could lead to arbitrary code execution, potentially allowing an attacker to take full control of the device, disrupt network operations, or intercept sensitive data passing through the router. 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 vulnerability does not require user interaction and has a low attack complexity, making it accessible to a wide range of threat actors. The lack of available patches at the time of publication further exacerbates the risk for affected users. Given that the TOTOLINK N150RT is a consumer-grade router commonly used in small offices and home environments, exploitation could serve as a foothold for attackers to pivot into larger networks or to create botnets for distributed denial-of-service (DDoS) attacks.

For European organizations, particularly small and medium enterprises (SMEs) and residential users relying on TOTOLINK N150RT routers, this vulnerability poses a significant risk. Compromise of these routers could lead to unauthorized access to internal networks, interception of confidential communications, and disruption of internet connectivity. In sectors where network availability and data confidentiality are critical—such as healthcare, finance, and government—such an attack could result in operational downtime, data breaches, and regulatory non-compliance. Additionally, compromised routers could be leveraged as part of larger botnets, contributing to broader cyberattacks that may indirectly affect European organizations. The high severity and ease of exploitation mean that attackers could rapidly weaponize this vulnerability, especially in environments where firmware updates are infrequent or unsupported. The lack of authentication requirement further increases the attack surface, as attackers can target devices directly over the internet without needing credentials or user interaction.

Immediately identify all TOTOLINK N150RT devices running firmware version 3.4.0-B20190525 within the network using asset management tools or network scanning. Isolate affected devices from critical network segments to limit potential lateral movement in case of compromise. Monitor network traffic for unusual activity originating from or targeting these routers, including unexpected outbound connections or anomalous DNS queries. Implement network-level protections such as firewall rules to restrict access to router management interfaces from untrusted networks, ideally limiting access to internal IP ranges only. If possible, disable remote management features on the affected routers to reduce exposure. Engage with TOTOLINK support channels to obtain any available firmware updates or patches; if none are available, consider replacing affected devices with models from vendors with active security support. Educate users and administrators about the risks of using outdated firmware and the importance of timely updates. Deploy intrusion detection/prevention systems (IDS/IPS) with signatures or heuristics capable of detecting exploitation attempts targeting the /boafrm/formVlan endpoint or buffer overflow patterns. Regularly back up router configurations and maintain an incident response plan to quickly remediate any detected compromises.