This indicates an attack attempt against an Remote Command Injection vulnerability in elFinder.
The vulnerability is due to an error in the vulnerable application when handling a maliciously crafted request. A remote attacker can exploit this to execute arbitrary code within the context of the target system.
elFinder version 2.1.58 and prior
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.