This indicates an attempt to exploit a remote Code Execution vulnerability in WordPress Marketplace plugin.
The vulnerability is due to insufficient sanitizing of user supplied inputs in the application. A remote attacker may be able to exploit this to execute arbitrary code within the context of the application, via a crafted HTTP request.
WP Marketplace 2.4.0 and prior versions
System Compromise: Remote attackers can execute arbitrary code on vulnerable systems.
Upgrade to the latest version available from the website.