This indicates an attack attempt to exploit a remote Code Execution vulnerability in ElasticSearch.
The vulnerability is caused by an error when the vulnerable software handles a malicious HTTP request. A remote attacker may be able to exploit this to execute arbitrary code within the context of the application, via a crafted HTTP request.
For CVE-2014-3120: ElasticSearch 1.1.1 and prior
For CVE-2015-1427: ElasticSearch 1.4.2 and prior
System Compromise: Remote attackers can gain control of vulnerable systems.
Currently we are unaware of any vendor supplied patch for this issue.