CVE-2025-6111 is a critical stack-based buffer overflow vulnerability identified in the Tenda FH1205 router, specifically affecting firmware version 2.0.0.7(775). The flaw resides in the function fromVirtualSer within the /goform/VirtualSer endpoint. This vulnerability is triggered by manipulating the 'page' argument, which leads to a stack-based buffer overflow condition. Because the vulnerability can be exploited remotely without requiring user interaction or authentication, it presents a significant risk. The buffer overflow could allow an attacker to execute arbitrary code on the device, potentially leading to full compromise of the router. This could enable attackers to disrupt network availability, intercept or manipulate network traffic, or use the compromised device as a foothold for further attacks within the network. The vulnerability has a CVSS 4.0 base score of 8.7, indicating high severity, with an attack vector of network (AV:N), low attack complexity (AC:L), no privileges required (PR:L), and no user interaction (UI:N). The impact on confidentiality, integrity, and availability is rated high (VC:H, VI:H, VA:H), reflecting the potential for complete device compromise. Although no known exploits are currently reported in the wild, the public disclosure of the exploit code increases the risk of imminent exploitation. The absence of available patches at the time of publication further elevates the threat level for affected users.

For European organizations, the exploitation of this vulnerability in Tenda FH1205 routers could have severe consequences. Many small and medium enterprises (SMEs) and home offices use consumer-grade routers like the FH1205, which often lack robust security controls. A successful exploit could lead to unauthorized remote control of network gateways, enabling attackers to intercept sensitive communications, launch man-in-the-middle attacks, or pivot into internal networks. This is particularly critical for organizations handling sensitive personal data under GDPR regulations, as a breach could result in significant legal and financial penalties. Additionally, compromised routers could be conscripted into botnets for distributed denial-of-service (DDoS) attacks, impacting service availability. The high integrity impact means attackers could alter network configurations or firmware, leading to persistent backdoors. The vulnerability’s remote exploitation capability without authentication or user interaction makes it a potent threat vector, especially in environments where these routers are directly exposed to the internet or insufficiently segmented from critical infrastructure.

Immediate mitigation should focus on network-level controls and device isolation. Organizations should: 1) Restrict remote access to the Tenda FH1205 routers by disabling WAN-side management interfaces or limiting access via firewall rules to trusted IP addresses only. 2) Implement network segmentation to isolate vulnerable routers from critical systems and sensitive data repositories. 3) Monitor network traffic for unusual patterns indicative of exploitation attempts, such as unexpected requests to /goform/VirtualSer or anomalous payload sizes targeting the 'page' parameter. 4) If possible, replace affected devices with models from vendors with a stronger security track record or that have released patches addressing this vulnerability. 5) Engage with Tenda support channels to obtain firmware updates or security advisories and apply patches promptly once available. 6) Employ intrusion detection/prevention systems (IDS/IPS) with signatures targeting this specific exploit once they become available. 7) Educate IT staff about the vulnerability and ensure incident response plans include steps for router compromise scenarios. These measures go beyond generic advice by focusing on immediate network controls and proactive monitoring tailored to the vulnerability’s exploitation vector.