This indicates an attack attempt to exploit an Arbitrary File Upload vulnerability in Tiki Wiki ELFinder.
The vulnerability is due to insufficient sanitizing of user supplied inputs in the application when handling a crafted request. A remote attacker can exploit this to upload arbitrary files and by making a direct request to the file, also execute the script file uploaded.
Tiki Wiki ELFinder Version 2.0
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.