This indicates an attack attempt to exploit a stack-overflow vulnerability in Apple Safari.
This issue is caused by an error when the vulnerable software handles an HTML file with a malformed CSS style. It may allow remote attackers to crash the vulnerable software by sending a crafted web page.
Apple Safari 4.0.4 & Google Chrome 4.0.249
System Comromise: Remote attackers can crash the vulnerable systems.
Upgrade to the latest version, available from the vendor's web site: