This indicates an attack attempt against a Directory Traversal vulnerability in ElasticSearch.
The vulnerability is due to insufficient sanitizing of user supplied inputs in the application while handling maliciously crafted requests. A remote attacker can exploit this to execute or upload arbitrary files, or reveal the content of arbitrary files anywhere on the web server.
ElasticSearch 1.4.x before 1.4.5
ElasticSearch 1.5.x before 1.5.2
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.