CVE-2025-11677 is a use-after-free vulnerability classified under CWE-416 found in the warmcat libwebsockets library, version 3. The flaw exists in the WebSocket server handshake function lws_handshake_server, specifically when the user application provides a callback function that handles the LWS_CALLBACK_HTTP_CONFIRM_UPGRADE event. This callback is part of the HTTP upgrade process to WebSocket protocol. Improper handling of memory during this callback can lead to a use-after-free condition, where the server attempts to access memory that has already been freed. This can cause undefined behavior, including crashes or denial of service (DoS). The vulnerability requires no authentication and no user interaction but has a high attack complexity, meaning exploitation demands specific conditions and knowledge of the target configuration. The CVSS v4.0 score is 6.3 (medium severity), reflecting the limited impact scope (denial of service only) and the complexity of exploitation. No known public exploits exist yet, and no patches have been linked, indicating the need for vendor action and user vigilance. The vulnerability affects libwebsockets version 3, a widely used lightweight WebSocket library in embedded systems, IoT devices, and web servers.

For European organizations, the primary impact of CVE-2025-11677 is the potential for denial of service attacks against services relying on libwebsockets version 3. This could disrupt real-time communications, IoT device management, or web applications that use WebSocket protocols for interactive features. Critical infrastructure sectors such as energy, transportation, and telecommunications that use embedded systems or web services with libwebsockets could experience service outages, impacting operational continuity. Although the vulnerability does not allow code execution or data breaches, the denial of service could degrade service availability and reliability, leading to financial losses and reputational damage. The medium severity and high attack complexity reduce the likelihood of widespread exploitation but do not eliminate risk, especially in targeted attacks against high-value assets.

Organizations should audit their use of libwebsockets version 3, particularly any custom callback implementations handling LWS_CALLBACK_HTTP_CONFIRM_UPGRADE. Until an official patch is released, consider disabling or restricting the use of this callback if feasible. Employ runtime memory protection tools and fuzz testing to detect anomalous behavior related to WebSocket handshake processing. Monitor vendor communications for security updates and apply patches promptly once available. Network-level protections such as Web Application Firewalls (WAFs) can help detect and block malformed WebSocket upgrade requests that might trigger the vulnerability. Additionally, implement robust monitoring and alerting for service crashes or abnormal terminations in WebSocket servers. For embedded or IoT devices, coordinate with device manufacturers to ensure firmware updates address this issue.