keycloak: XSS-Vulnerability with response_mode=form_post

A flaw was found in Keycloak 3.4.3.Final, 4.0.0.Beta2, 4.3.0.Final. When using 'responsemode=formpost' it is possible to inject arbitrary Javascript-Code via the 'state'-parameter in the authentication URL. This allows an XSS-Attack upon succesfully login...