This indicates an attack attempt to exploit a Remote Code Injection Vulnerability in vBulletin.
The vulnerability is due to insufficient sanitizing of user-supplied input. An attacker can exploit this issue to inject arbitrary code, which will be executed in the target user's system.
vBulletin version 5.5.5 to version 5.6.2
System Compromise: Remote attackers can gain control of vulnerable systems.
Currently, we are unaware of any vendor supplied patch for this issue.