CVE 2010-1417
The Cascading Style Sheets (CSS) implementation in WebKit in Apple Safari before 5.0 on Mac OS X 10.5 through 10.6 and Windows, and before 4.1 on Mac OS X 10.4, allows remote attackers to execute arbitrary code or cause a denial of service (memory corruption and application crash) via HTML content that contains multiple :after pseudo-selectors.
See the 
CVE page on Mitre.org
for more details.
