How iOS 5.1 Jailbreak with GreenPois0n Absinthe v2.0 is working

This is at the limit of being art! you need to be a good developer to understand this

GreenPois0n Absinthe was built upon @pod2g’s Corona untether jailbreak to create the first public jailbreak for the iPhone 4S and iPad 2 on for the 5.0.1 firmware. In this paper, we present a chain of multiple exploits to accomplish sandbox breakout, kernel unsigned code injection and execution that result in a fully-featured and untethered jailbreak.

Corona is an acronym (sic) for "racoon", which is the primary victim for this attack. A format string vulnerability was located in racoon’s error handling routines, allowing the researchers to write arbitrary data to racoon’s stack, one byte at a time, if they can control racoon’s configuration file. Using this technique researchers were able to build a ROP payload on racoon’s stack to mount a rogue HFS volume that injects code at the kernel level and patch its code-signing routines.

The original Corona untether exploit made use of the LimeRa1n bootrom exploit as an injection vector, to allow developers to disable ASLR and sandboxing, and call racoon with a custom configuration script. This however left it unusable for newer A5 devices like the iPad2 and iPhone 4S, which weren’t exploitable to LimeRa1n, so another injection vector was needed.

via iClarified)

This hack be applied to nearly all iPads, the iPhone 3G, 4 and 4S, third and fourth generation iPod touch media players, and the second-generation Apple TV. Support for the new 8GB iPad 2, which features a custom-designed A5 chip, will be available soon!