This indicates an attack attempt against a Remote Code Execution vulnerability in Atlassian JIRA and HipChat for Atlassian JIRA plugin.
The vulnerability is caused by an improper validation of user supplied data when the vulnerable application handles a maliciously crafted request. An attacker can exploit this to gain access to execute arbitrary code in the context of the vulnerable application via a crafted request.
Atlassian JIRA version 6.4.11 and prior
HipChat For Atlassian JIRA plugin version 6.30.0 and prior
System Compromise: Remote attacker can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.