The evasi0n jailbreak leverages an impressive set of vulnerabilities that collectively enable users to fully jailbreak their iOS 6.x based device. While the user land component was an impressive feat on its own, the kernel exploit used to evade sandbox restrictions as well as code signing, holds an equally impressive array of sophisticated exploitation techniques. In this blog entry, we detail the leveraged kernel vulnerability and show how evasi0n goes to great lengths to overcome security hardenings such as kernel address space randomization and kernel address space protection.
read more.......http://blog.azimuthsecurity.com/2013/02/from-usr-to-svc-dissecting-evasi0n.html