We reported only a while back of Apple seeding the Gold Master release of the iOS 4.2 for developers. The good news is that the existing version of the Redsn0w based on the Limera1n exploit by Geohot is fully capable of jailbreaking all Apple devices based on the iOS 4.2.
From the iPhone Dev Team blog:
Redsn0w jailbreaks today’s 4.2 GM seed, simply by pointing redsn0w at the 4.1 IPSW (rather than the 4.2 one)… However, if all you want to do is enable afc2 (to use iFunBox or other file browsers), or to tweak settings like Battery % and Homescreen wallpapers, then go for it (if you have valid paid access to the GM seed)…
With this confirmed and if you are one of those willing to go on jailbreaking adventure the Redsn0w 0.9.6b2 will jailbreak the following devices:
As for the procedures you can follow the given step by step guide on how to jailbreak your iOS 4.2 GM with Redsn0w. One warning for all those with unlocked iPhones, they must prevent updating to the iOS 4.2. I would recommend they wait till the release of the Ultrasn0w unlock.
1. Download iOS 4.2 and iOS 4.1.
2. You will now need to update the iOS 4.2 firmware. this will be done using the IPSW file downloaded using the Beta 2 of the iTunes 10.1.
3. Initiate Redsn0w 0.9.6b2 and select iOS 4.1 to start the jailbreak. Remember you don’t need to point to the iOS 4.2 since it is not the final version.
4. Install Cydia and move on with hitting Next. Once this is being done, ensure that your iOS device is powered off and plugged to your computer. You will have to hold the Power Button and the Home button for a while after which you can release the Power button only. You will have to hold the Home button until the installation procedure begins.
5. That’s it. Redsn0w will now take charge and continue with jailbreaking your iOS device. Your iPhone or the iPod Touch will restart automatically to seal the jailbreak.