A permission issue was found in Elasticsearch versions before 5.6.15 and 6.6.1 when Field Level Security and Document Level Security are disabled and the _aliases, _shrink, or _split endpoints are used . If the elasticsearch.yml file has xpack.security.dls_fls.enabled set to false, certain permission checks are skipped when users perform one of the actions mentioned above, to make existing data available under a new index/alias name. This could result in an attacker gaining additional permissions against a restricted index.
Elasticsearch before 1.6.1 allows remote attackers to execute arbitrary code via unspecified vectors involving the transport protocol. NOTE: ZDI appears to claim that CVE-2015-3253 and CVE-2015-5377 are the same vulnerability