This indicates an attempt to exploit an Arbitrary File Upload vulnerability in PhpCollab.
The vulnerability is due to insufficient sanitizing of user supplied inputs when handling a crafted request. It allows a remote attacker to upload an arbitrary file onto vulnerable systems via a crafted HTTP request.
PhpCollab 2.5.1 and prior
System Compromise: Remote attackers can gain control of vulnerable systems.
Upgrade to the latest version available from the vendor.