This indicates an attack attempt against an Arbitrary File Upload vulnerability in PHP-Fusion.
The vulnerability is due to insufficient sanitizing of user supplied inputs when handling a crafted file upload. It allows a remote attacker to upload an arbitrary file onto vulnerable systems via a crafted HTTP request.
PHP-Fusion version 9.03.00 and prior
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.