This indicates an attack attempt to perform an Arbitrary File Upload vulnerability in Joomla Plugin Fabrik.
The vulnerability is due to a design flaw in the vulnerable application when handling a file upload request without authentication. A remote attacker may be able to exploit this to execute arbitrary code within the context of the application, by uploading an arbitrary file without any authentication.
Joomla Plugin Fabrik
System Compromise: Remote attackers can gain control of vulnerable systems.
Upgrade to the latest version, available from the website.