This indicates an attack attempt to exploit a Memory Corruption vulnerability in WebKit, a component of Apple Safari.
The vulnerability is due to how the vulnerable software handles a CSS style for a title element. An attacker can exploit this by tricking an unsuspecting user into visiting a malicious webpage and execute arbitrary script code within the context of the application.
Apple Computer Safari prior to 5.1.7
System Compromise: Remote attackers can execute arbitrary script code within the security context of the targeted user.
Apply the most recent upgrade or patch from the vendor.