This indicates an attack attempt to exploit a Code Execution vulnerability in Wordpress CM Download Manager plugin.
The vulnerability is due to insufficient sanitizing of user supplied inputs when handling a maliciously crafted HTTP request. A remote attacker may be able exploit this to execute arbitrary code within the context of the application via a crafted request.
WordPress CreativeMinds CM Downloads Manager plugin before 2.0.4
System Compromise: Remote attackers can gain control of vulnerable systems
Apply the most recent upgrade or patch from the vendor.