An error was found in the X-Pack Security TLS trust manager for versions 5.0.0 to 5.5.1. If reloading the trust material fails the trust manager will be replaced with an instance that trusts all certificates. This could allow any node using any certificate to join a cluster. The proper behavior in this instance is for the TLS trust manager to deny all certificates.
Elasticsearch X-Pack Security versions 5.0.0 to 5.4.3, when enabled, can result in the Elasticsearch _nodes API leaking sensitive configuration information, such as the paths and passphrases of SSL keys that were configured as part of an authentication realm. This could allow an authenticated Elasticsearch user to improperly view these details.