The queueing primitives in IOMobileFrameBuffer in Apple iOS before 4.2.9 and 4.3.x before 4.3.4 do not properly perform type conversion, which allows local users to gain privileges via a crafted application.
http://support.apple.com/kb/HT4803
http://support.apple.com/kb/HT4802
http://lists.apple.com/archives/security-announce/2011//Jul/msg00001.html
http://lists.apple.com/archives/security-announce/2011//Jul/msg00000.html