Elasticsearch Alerting and Monitoring in versions before 6.4.1 or 5.6.12 have an information disclosure issue when secrets are configured via the API. The Elasticsearch _cluster/settings API, when queried, could leak sensitive configuration information such as passwords, tokens, or usernames. This could allow an authenticated Elasticsearch user to improperly view these details.
In Elasticsearch versions 6.0.0-beta1 to 6.2.4 a disclosure flaw was found in the _snapshot API. When the access_key and security_key parameters are set using the _snapshot API they can be exposed as plain text by users able to query the _snapshot API.