In versions of Spring Authorization Server 1.5.0 through 1.5.7, the authorization endpoint performs insufficient validation of the request_uri parameter. An attacker can craft a request containing an invalid request_uri paired with an unvalidated redirect_uri, which can result in an open redirect to an attacker-controlled site.
Upgrade to Spring Authorization Server 1.5.8 (OSS) or 1.5.7.1 (Enterprise Support customers). No additional mitigation is required after upgrading.