Improper Authentication in Spring Authorization Server

Spring Authorization Server versions 1.0.0 - 1.0.5, 1.1.0 - 1.1.5, 1.2.0 - 1.2.2 and older unsupported versions are susceptible to a PKCE Downgrade Attack for Confidential Clients.

Specifically, an application is vulnerable when a Confidential Client uses PKCE for the Authorization Code Grant.

An application is not vulnerable when a Public Client uses PKCE for the Authorization Code Grant.