This indicates an attack attempt against an arbitrary File Upload vulnerability in GetSimple CMS.
The vulnerability is due to insufficient sanitizing of user supplied inputs when handling an crafted HTTP request. It allows a remote attacker to upload an arbitrary file onto vulnerable systems via a crafted HTTP request.
GetSimple CMS 3.2.1
System Compromise: Remote attackers can gain control of vulnerable systems.
Currently we are unaware of any vendor supplied patch for this issue.