We’ve been getting a lot of emails lately about this and so we thought it was a good idea to do a dedicated post on it to answer this question once and for all.
With any modern version of iOS, in order to downgrade a device to a previous version of the system, users must have a backed up SHSH blob of the version they’re trying to upgrade/downgrade to, otherwise the process will just fail. This is done to protect devices from vulnerabilities present in earlier versions of iOS but it also stops jailbreakers from applying tweaks that might not be available on the current iOS.
With every iOS update released, attentions quickly turn to the hacking community to see what the state of play is regarding jailbreaking and unlocking. As was the case with the previous security update released by Apple some 12 days ago, you can still unlock your iPhone 4 running 4.3.5, but it will require purchase of the controversial yet effective Gevey SIM in order to work.
Untethered 4.3.5 jailbreak: A few hours ago, iOS 4.3.5 was released publicly, to the surprise of many. The new update, the second of its kind in one month, is not expected to receive an untethered jailbreak anytime soon, therefore users should refrain from updating at this point in time.
Earlier today, Apple released the new iOS 4.3.5 firmware to patch a critical security issue with certificate verification in iOS. It is important to note that there is currently no untethered jailbreak solution available for both iOS 4.3.4 (which was released on 15th July) and the just released iOS 4.3.5. Do NOT update to 4.3.5 or 4.3.4 if you want to keep your untethered jailbreak.
It's been little over a week since Apple scrambled to release iOS 4.3.4 to plug the easily jailbreakable 4.3.3, and already another update has surfaced which addresses "certificate validation" vulnerabilities, and unfortunately, just like iOS 4.3.4, those of you that own an iPad 2 on iOS 4.3.5 can no longer jailbreak, not even tethered like other devices.
Jailbreak 4.3.5 with Redsn0w: Apple has unexpectedly pushed out an incremental update for iOS 4.3.x, and it is dubbed as iOS 4.3.5. This minor release is no more than a security update, aiming to patch issues with certificate verification. The good news is that we have tested it and can confirm that the current version of Redsn0w can jailbreak the just released iOS 4.3.5 on iPhone 4, 3GS, and iPod touch 4G/3G.
Just months before iOS 5 is released and ten days after iOS 4.3.4 came out, one wouldn't expect to ever hear about iOS 4.3.5. It now turns out that yet another update for iOS 4.3 has been uploaded to Apple's servers, allegedly fixing a critical security issue.