A flaw was found in Keycloak. A Keycloak server configured to support mTLS authentication for OAuth/OpenID clients does not properly verify the client certificate chain. A client that possesses a proper certificate can authorize itself as any other client, therefore, access data that belongs to other clients.
https://bugzilla.redhat.com/show_bug.cgi?id=2191668
https://access.redhat.com/security/cve/CVE-2023-2422
https://access.redhat.com/errata/RHSA-2023:3892
https://access.redhat.com/errata/RHSA-2023:3888
https://access.redhat.com/errata/RHSA-2023:3885