Eminent jailbreak developer iH8sn0w has posted a screenshot (as a proof) showing iPhone 4S running iOS 5.0.1 but with iOS 5.1 baseband 2.0.10. This implies that the hacker has successfully downgraded from iOS 5.1 to iOS 5.0.1 firmware on A5 based iPhone 4S. Last week, Steven confirmed to have discovered a loophole in Apple’s APTicket system allows downgrading from iOS 5.1 to iOS 5.0.1 on A5/A5X devices but did not shared any video or image to corroborate his meaty claim.
As evident, a 4S device downgraded back to 5.0.1 doesn’t have the 5.1 baseband downgraded. This is because upon every restore the baseband is flashed and the current baseband Apple is signing is for 5.1 IPSW.
To date, restoring iPad 2 and iPhone 4S to old firmware is not possible with any of the tools available – TinyUmbrella or iFaith- since iOS 5 has new SHSH mechanism (with APTicket). iOS firmware downgrade is only possible from iOS 5.x to iOS 4.x (however, you must have saved SHSH blobs for iOS 4.x), but doesn’t work for downgrading between versions of iOS 5.x (for instance, iOS 5.1 to iOS 5.0.1). Yes, SHSH blobs will ‘always’ be required unless someone finds an untethered bootrom exploit.
We don’t have a firm ETA yet, but if you consider they’re teasing us with it already, it’s probably right around the corner. However, iH8snow has confirmed that he is planning to release it after a 5.1 jailbreak or the next iOS software update is out. Until iOS 5.1 Jailbreak for A5 devices goes live, we’ll have to hold our breath and wait.