Good news for owners of the iPhone 4S and iPad 2 looking to downgrade from iOS 5.1. iH8sn0w announced the discovery of a loophole that makes it possible to downgrade any A5 device to iOS 5.0.1. Not only this, but the developer has successfully restored an iPad 2 to iOS 5.0.1 using the procedure.
Found a loophole in Apple's apticket system. Restored my iPad 2 to 5.0.1 from 5.1. Works on all A5 devices. :)
— iH8sn0w (@iH8sn0w) March 25, 2012
Downgrading an iPhone, from iOS 5 to 4.3.3 for example, requires saved SHSH blobs since Apple stops signing older firmware when an update is released. It's likely that the loophole iH8sn0w has found will also require saved SHSH blobs to work.
Apple isn't playing nice with the jailbreaking community and has recently started blocking devices from restoring to older firmware. If you accidently updated to 5.0.1 and want to restore your device, hacker iH8sn0w has a new solution for you. iFaith v1.4 allows you to save your iOS device’s SHSH blobs which should allow you to downgrade your device in the future.
Unfortunately it doesn't support A5 devices. Meaning if you recently purchased an iPhone 4S, or upgraded to iOS 5.0.1, you're still out of luck for now. A4 owners are being urged by the jailbreaking community to download the latest update of iFaith and to save their SHSH blobs immediately.