Apache CXF before 3.3.4 and 3.2.11 provides all of the components that are required to build a fully fledged OpenId Connect service. There is a vulnerability in the access token services, where it does not validate that the authenticated principal is equal to that of the supplied clientId parameter in the request. If a malicious client was able to somehow steal an authorization code issued to another client, then they could exploit this vulnerability to obtain an access token for the other client.