This indicates an attack attempt against a Security Bypass vulnerability in Oracle Java JRE.
The vulnerability is due to a design flaw in the application when loading a crafted Java applet. An attacker can exploit this by tricking an unsuspecting user into visiting a webpage containing a malicious Java applet and execute arbitrary code within the context of the application.
Oracle Java Runtime Environment (JRE) 7 Update 21 and earlier
System Compromise: Remote attackers can execute arbitrary Java Code within the context of the vulnerable systems.
Apply the most recent upgrade or patch from the vendor.