The head of iPhone Dev Team has announced the release of a new Redsn0w version which supports downgrades to older versions of iOS firmwares from its interface. Users are still required to have their SHSH blobs saved.
MuscleNerd writes on the Dev Team blog that “Jailbreakers with devices that pre-date the iPad2 will always be able to downgrade (with SHSH blobs) to previous firmware versions due to geohot’s limera1n exploit, which allows us to bypass the restrictions that Apple places on restores.”
“But until now, that ability has been limited to those older devices,” he says, adding that “Starting with redsn0w version 0.9.11b1, those with newer devices (iPad2, iPad3, and iPhone4S) can join the downgrade fun too!”
MuscleNerd explains that their flagship jailbreak tool, Redsn0w, now supports IPSW restores, and that the first stab at this feature enables downgrades for people who accidentally updated to newer iOS versions, thus losing their jailbreak.
“In a radical departure from previous versions of redsn0w, it now directly supports restoring IPSWs to your device. The first use of this new feature implements a hack that allows A5 downgrades without a bootrom-level exploit,” MuscleNerd writes.
As usual, the Dev Team leader is careful to point out some important aspects regarding this procedure.
For example, users will not be able to perform the downgrade without the personalized SHSH blobs for their device at that particular (lower) firmware. In other words, if you haven't been careful to save them, you're out of luck.
“You need to have fetched those blobs while the signing window was open, using either Cydia’s built-in TSS@Home feature, or with TinyUmbrella. The new Restore screen of redsn0w lets you choose either the remote blobs or local ones (for the earlier firmware). If you don’t know where TinyUmbrella put your blobs, TinyUmbrella has a button that will show you (copy them out of that folder and feed them to redsn0w).”
Another important point is that “the A5 downgrade method actually updates to the latest firmware before downgrading to the earlier one,” which means that it updates your baseband to the newest version, hence it shouldn’t be used by iPhone 4S owners who rely on unofficial unlocks.
More important notes regarding Redsn0w 0.9.11b1 can be found at the Dev Team blog