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Apple servers briefly enabled signing of older iOS firmwares, allowing users to downgrade to earlier versions

Apple's servers started to sign older versions of iOS for a number of hours on Wednesday night, an issue that gave iPhone and iPad owners a brief opportunity to downgrade iOS to an earlier release, with some hardware found to be downgradable to iOS 6.

The servers were signing firmware versions for iOS from the latest version 11.2.2 update, released earlier this week, to as early as version 6, according to Reddit. The version available to users shown on tracker depended on the model of iPhone used, with newer devices able to revert as far back as the version of iOS available at its initial release.

By signing older versions, this allowed any user to take advantage of iTunes' firmware restore facility to use the earlier versions. This also made it easier for users wanting to jailbreak their devices, by allowing the iOS device to downgrade to a breakable version of the operating system.

The signed iOS bonanza took place for a number of hours before Apple's servers reverted back to their previous state, where only the more recent releases for each iPhone were signed and usable. It is highly likely that this was either a bug or a mistake performed by Apple employees, and was completely unintentional.

Apple has yet to comment on the event.

Shortly before the mass firmware signing took place, another post on Reddit noted that some iOS devices no longer had any signed firmware versions available. At one point, the first to third-generation iPads, iPad mini, third and fifth-generation iPod touch, and the iPhone 4S did not have a restorable version of iOS, after Apple's servers unsigned iOS 9.3.5 and iOS 5.1.1.

Apple has a policy of preventing older versions of iOS from being used on its mobile hardware, with legacy operating systems unsigned as newer firmware updates become available. Unsigning stops users from reinstalling legacy versions, forcing them onto newer releases that cannot be jailbroken, offer more security, and have the latest features available for Apple's hardware.