This indicates an attack attempt to exploit a remote Code Execution Vulnerability in FreePBX.
The vulnerability is due to an user input invalidation error when handling a crafted HTTP request. A remote attacker could exploit this to execute arbitrary code execution within the context of the application, via a crafted HTTP request.
FreePBX Project FreePBX 2.10
FreePBX Project FreePBX 2.11
FreePBX Project FreePBX 12
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.