This indicates an attack attempt against a Cross-Site Request-Forgery vulnerability in WordPress Plugin Facebook for WordPress.
The vulnerability is due to insufficient sanitization of user supplied inputs in the application. An attacker may exploit this to cause the server to perform certain actions in the context of an authorized user's session and gain unauthorized access to the affected application.
WordPress Facebook for WordPress plugin from 3.0.0 to 3.0.3
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.