WebKit, as used in Apple Safari before 5.0.4 and iOS before 4.3, does not properly handle unspecified "cached resources," which allows remote attackers to cause a denial of service (resource unavailability) via a crafted web site that conducts a cache-poisoning attack.
https://exchange.xforce.ibmcloud.com/vulnerabilities/66001
http://www.securitytracker.com/id?1025182
http://support.apple.com/kb/HT4566
http://support.apple.com/kb/HT4564
http://lists.apple.com/archives/security-announce/2011//Mar/msg00004.html
http://lists.apple.com/archives/security-announce/2011//Mar/msg00003.html