WebKit, as used in Apple iOS before 6, allows remote attackers to execute arbitrary code or cause a denial of service (memory corruption and application crash) via a crafted web site.
https://exchange.xforce.ibmcloud.com/vulnerabilities/78725
http://support.apple.com/kb/HT5503
http://lists.apple.com/archives/security-announce/2012/Sep/msg00003.html