The Chronic dev team has just released GreenPois0n RC5 jailbreaking tool which can be used to jailbreak iDevices running the latest iOS 4.2.1 firmware. Only catch here is that (for now) GreenPois0n RC5 is available only for Mac and it is not a stable release (RC5 – Release candidate 5). GreenPois0n for Windows and Linux is expected to arrive soon.
With GreenPois0n RC5, you will be able to jailbreak iOS 4.2.1 (untethered) on iPhone 4, iPhone 3GS, iPod Touch 4G/3G/2G, iPad and Apple TV 2G. Unlike Redsnow 0.9.7, Greenpois0n RC5 will not need any 4.2b3 SHSH Blobs saved on Cydia for Untethered Jailbreak.
Download GreenPois0n RC5
You can download GreenPois0n RC5 from Greenpois0n RC5 or use this mirror. You can check the guide given below to use GreenPois0n RC5 to jailbreak iOS 4.2.1, but be aware of this being an unstable release and expect some problems if you don’t follow the procedure carefully.
Update: Greenpois0n RC5_2 has been released which fixes some of the previous issues. Download it here or here.
Update: GreenPois0n RC5 released for Windows. Download at greenpois0n.com or here.
How to Jailbreak iOS 4.2.1 using GreenPoisOn RC5?
Disclaimer: The guide is purely for informational and educational purposes only. Jailbreak your device at your own risk.
Do not proceed if you rely on carrier unlock. Ultrasn0w doesn’t support this baseband yet.
1. Download GreenPois0n RC5 from the links given above.
2. Connect your iDevice running iOS 4.2.1 to the USB of your mac.
3. Start GreenPois0n RC5 and click on Jailbreak button. Follow the on-screen instructions to put your device in the DFU mode.
4. Click again on Jailbreak button of Greenpois0n to start the jailbreaking process.
5. Wait for GreenPois0n to complete its steps. Once it’s complete, you will see a “Loader” icon on the springboard. Tap on it and install Cydia.
Voila! Your iDevice is now jailbroken with iOS 4.2.1! Thanks Blogsdna!