This indicates an attack attempt against an arbitrary File Upload vulnerability in the Asset Manager plug-in for WordPress.
The vulnerability is caused by an error when the vulnerable software handles a malicious HTTP request with a crafted URI. It allows a remote attacker to upload an arbitrary file via sending a crafted URI to a vulnerable application.
WordPress Asset Manager 0.2
System Compromise: Remote attackers can gain control of vulnerable systems.
Currently we are unaware of any vendor supplied patch for this issue.