CVE-2025-11676 identifies an improper input validation vulnerability (CWE-20) in the Universal Plug and Play (UPnP) modules of the TP-Link TL-WR940N V6 router, specifically affecting firmware versions up to Build 220801. The flaw allows unauthenticated attackers located on adjacent networks—such as those connected to the same local network segment or Wi-Fi—to send malformed input to the UPnP service, causing the device to crash or become unresponsive, resulting in a denial-of-service (DoS) condition. The vulnerability arises because the UPnP module fails to correctly validate incoming data, permitting crafted packets to disrupt normal operation. The CVSS v4.0 score of 7.1 reflects a high severity, with an attack vector classified as adjacent network (AV:A), no privileges or user interaction required, and a high impact on availability. No known exploits have been reported in the wild, but the lack of authentication and ease of triggering the DoS condition make this a significant risk. The affected product, TL-WR940N V6, is a widely deployed consumer and small business router, often used in home and small office environments. The absence of a patch link indicates that a fix may not yet be publicly available, emphasizing the need for interim mitigations.

For European organizations, particularly small and medium enterprises (SMEs) and home offices relying on TP-Link TL-WR940N V6 routers, this vulnerability poses a risk of network disruption through denial-of-service attacks. The inability to access network resources or the internet due to router crashes can lead to operational downtime, productivity loss, and potential security monitoring gaps. Critical services dependent on continuous connectivity may be interrupted, affecting business continuity. Since the attack requires adjacency, internal threat actors or compromised devices within the local network could exploit this vulnerability to disrupt operations. Additionally, public or semi-public Wi-Fi networks using these routers could be targeted by nearby attackers, increasing exposure. The lack of authentication and user interaction requirements lowers the barrier for exploitation, making the threat more immediate. While no data confidentiality or integrity impact is indicated, availability degradation alone can have significant operational consequences.

Organizations should prioritize the following specific mitigations: 1) Monitor TP-Link's official channels for firmware updates addressing this vulnerability and apply patches promptly once available. 2) Disable UPnP functionality on the TL-WR940N V6 routers if it is not essential for network operations, as this reduces the attack surface. 3) Segment networks to restrict access to router management and UPnP services, limiting exposure to only trusted devices. 4) Employ network access controls to prevent unauthorized devices from connecting to the local network or Wi-Fi, reducing the risk of adjacent attackers. 5) Regularly audit network devices for firmware versions and configuration settings to ensure compliance with security best practices. 6) Consider replacing affected routers with models that have confirmed security updates if patching is delayed. 7) Educate users about the risks of connecting unknown devices to internal networks to minimize insider threats. These steps go beyond generic advice by focusing on configuration changes and network architecture adjustments tailored to this vulnerability.