Spring Security versions 5.5.x prior to 5.5.1, 5.4.x prior to 5.4.7, 5.3.x prior to 5.3.10 and 5.2.x prior to 5.2.11 are susceptible to a Denial-of-Service (DoS) attack via the initiation of the Authorization Request in an OAuth 2.0 Client Web and WebFlux application. A malicious user or attacker can send multiple requests initiating the Authorization Request for the Authorization Code Grant, which has the potential of exhausting system resources using a single session or multiple sessions.

Spring Security 5.4.x prior to 5.4.4, 5.3.x prior to 5.3.8.RELEASE, 5.2.x prior to 5.2.9.RELEASE, and older unsupported versions can fail to save the SecurityContext if it is changed more than once in a single request.A malicious user cannot cause the bug to happen (it must be programmed in). However, if the application's intent is to only allow the user to run with elevated privileges in a small portion of the application, the bug can be leveraged to extend those privileges to the rest of the application.