CVE-2025-5911 is a critical buffer overflow vulnerability identified in the TOTOLINK EX1200T router, specifically affecting firmware versions up to 4.1.2cu.5232_B20210713. The vulnerability resides in an unknown functionality within the HTTP POST request handler component, particularly in the /boafrm/formDMZ endpoint. An attacker can exploit this flaw by sending a crafted HTTP POST request to the affected endpoint, causing a buffer overflow condition. This overflow can potentially allow remote code execution or denial of service without requiring authentication or user interaction. The vulnerability is remotely exploitable over the network, increasing its risk profile. The CVSS v4.0 score is 8.7 (high severity), reflecting the ease of exploitation (network vector, low attack complexity, no privileges or user interaction required) and the significant impact on confidentiality, integrity, and availability. Although no public exploit is currently known to be in the wild, the exploit code has been disclosed publicly, increasing the likelihood of exploitation attempts in the near future. The vulnerability affects the HTTP POST request handler, which is a critical component for router management and configuration, making successful exploitation potentially devastating to network security and device stability.

For European organizations, the exploitation of CVE-2025-5911 could lead to severe consequences. Compromised TOTOLINK EX1200T routers could allow attackers to gain unauthorized control over network infrastructure, leading to interception or manipulation of sensitive data, disruption of network services, or pivoting to internal systems for further attacks. This is particularly critical for small and medium enterprises (SMEs) and home office environments that commonly deploy consumer-grade routers like TOTOLINK EX1200T without advanced security monitoring. The vulnerability could also be leveraged to create botnets or launch distributed denial-of-service (DDoS) attacks, affecting broader network availability. Given the router’s role as a gateway device, exploitation could undermine the confidentiality, integrity, and availability of organizational networks, potentially causing operational downtime, data breaches, and regulatory compliance issues under GDPR and other European data protection laws.

Organizations should immediately verify if they are using TOTOLINK EX1200T devices with firmware versions up to 4.1.2cu.5232_B20210713. Since no official patch links are currently provided, it is critical to: 1) Restrict network access to the router’s management interface, ideally limiting it to trusted internal IP addresses and disabling remote management over WAN. 2) Employ network segmentation to isolate vulnerable devices from critical infrastructure. 3) Monitor network traffic for unusual POST requests targeting /boafrm/formDMZ or other suspicious activity indicative of exploitation attempts. 4) Consider replacing affected devices with models from vendors that provide timely security updates. 5) Regularly check TOTOLINK’s official channels for firmware updates addressing this vulnerability and apply patches promptly once available. 6) Implement intrusion detection/prevention systems (IDS/IPS) with signatures for this vulnerability to detect and block exploit attempts. 7) Educate IT staff about the vulnerability and ensure incident response plans include steps for compromised router scenarios.