updated 11:36 am EDT, Mon May 14, 2012
Reverses upgrades to iOS 5.1.1
The unofficial iPhone Dev Team has released a new version of redsn0w, its jailbreaking utility for iOS devices. The v0.9.11b4 update lets users restore old IPSW files to A5-based Apple devices, including the iPhone 4S, third-generation iPad, and iPad 2; previously, only devices prior to the iPad 2 could be downgraded, thanks to the limera1n exploit. The update means that A5 devices can now be downgraded from iOS 5.1.1 or 5.1 to 5.0.1.
A number of catches are in place. People must for instance have SHSH blobs associated with the earlier firmware, captured either through TinyUmbrella or Cydia's TSS@Home. Remote or local blobs can be used. The Dev Team also notes that the downgrade process actually updates to the latest firmware before downgrading, updating baseband at the same time, which will ruin most unofficial unlocks of the iPhone 4S except temporary SAM techniques. Apple should moreover be able to fix the exploit used for A5 downgrades, as reverse engineering shows the company is already aware of it.