The Restrictions (aka Parental Controls) implementation in Apple iOS before 6 does not properly handle purchase attempts after a Disable Restrictions action, which allows local users to bypass an intended Apple ID authentication step via an app that performs purchase transactions.
https://exchange.xforce.ibmcloud.com/vulnerabilities/78721
http://support.apple.com/kb/HT5503
http://lists.apple.com/archives/security-announce/2012/Sep/msg00003.html