It was found that SAML authentication in Keycloak 3.4.3.Final incorrectly authenticated expired certificates. A malicious user could use this to access unauthorized data or possibly conduct further attacks.
https://bugzilla.redhat.com/show_bug.cgi?id=CVE-2018-10894
https://access.redhat.com/errata/RHSA-2019:0877
https://access.redhat.com/errata/RHSA-2018:3595