Keycloak up to version 6.0.0 allows the end user token (access or id token JWT) to be used as the session cookie for browser sessions for OIDC. As a result an attacker with access to service provider backend could hijack user’s browser session.
https://bugzilla.redhat.com/show_bug.cgi?id=CVE-2019-3868
https://access.redhat.com/errata/RHSA-2019:2998