CVE-2021-4236 in web
Summary
by MITRE • 12/28/2022
Web Sockets do not execute any AuthenticateMethod methods which may be set, leading to a nil pointer dereference if the returned UserData pointer is assumed to be non-nil, or authentication bypass. This issue only affects WebSockets with an AuthenticateMethod hook. Request handlers that do not explicitly use WebSockets are not vulnerable.
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Analysis
by VulDB Data Team • 04/11/2025
This vulnerability resides in the websocket authentication mechanism of a software system where the authentication method hooks fail to execute properly during websocket connections. The flaw specifically impacts websocket implementations that have configured authentication methods through the AuthenticateMethod hook mechanism. When a websocket connection attempts to authenticate, the system does not invoke the configured authentication method, creating a critical security gap that can lead to either a denial of service through nil pointer dereference or complete authentication bypass.
The technical root cause involves a failure in the websocket protocol handling logic where the system assumes that authentication data will always be available through the UserData pointer returned by authentication methods. However, when the AuthenticateMethod hook is not executed, this pointer remains nil, causing a nil pointer dereference when subsequent code attempts to access the UserData structure. This condition creates a direct pathway for attackers to bypass authentication entirely since no proper authentication validation occurs during the websocket connection establishment process.
The operational impact of this vulnerability extends beyond simple authentication bypass to include potential system instability through denial of service conditions. When the websocket connection logic attempts to dereference a nil pointer during authentication processing, it results in application crashes or unexpected termination of the websocket service. This creates a scenario where legitimate users may experience service disruption while unauthorized users can potentially gain access to protected resources without proper authentication. The vulnerability specifically targets websocket implementations that utilize the AuthenticateMethod hook, making it a targeted issue for systems that rely on websocket-based communication with authentication requirements.
Systems affected by this vulnerability typically include web applications that use websocket protocols for real-time communication and require user authentication for access control. The impact is particularly severe in environments where websocket connections are used for sensitive operations or where authentication is critical for maintaining system security boundaries. Organizations using websocket-based services with configured authentication hooks are at risk of unauthorized access, data breaches, and potential system compromise. The vulnerability aligns with CWE-476 which describes null pointer dereference conditions, and represents a significant weakness in the authentication flow that violates standard security practices for websocket implementations.
Mitigation strategies should focus on ensuring that authentication methods are properly invoked during websocket connection establishment. The recommended approach involves implementing proper validation checks to verify that authentication methods are executed before proceeding with connection handling. Organizations should also consider implementing additional security controls such as connection rate limiting, access control lists, and monitoring for unauthorized websocket connections. The fix requires modification of the websocket protocol handler to ensure that the AuthenticateMethod hook is always invoked, regardless of the connection type, while also implementing proper null pointer checks in the authentication processing logic. This vulnerability demonstrates the importance of comprehensive security testing for protocol implementations and highlights the need for robust authentication validation across all connection types within web applications.