Red Hat Keycloak before version 2.4.0 did not correctly check permissions when handling service account user deletion requests sent to the rest server. An attacker with service account authentication could use this flaw to bypass normal permissions and delete users in a separate realm.
https://bugzilla.redhat.com/show_bug.cgi?id=1388988
https://access.redhat.com/errata/RHSA-2017:0873
https://access.redhat.com/errata/RHSA-2017:0872
http://www.securitytracker.com/id/1038180