[Guide] How to jailbreak iOS 4.2.1 using Redsn0w 0.9.6b4

We previously shared a guide on how to jailbreak iOS 4.2 using PwnAgeTool 4.1 for Mac. Now the Dev Team has updated their RedSn0w jailbreak tool to version 0.9.6b4 with support for jailbreaking iOS 4.2.1.

Redsn0w 0.9.6b4 is based on Geohot’s Limera1n bootrom exploit which has already pwned all current iOS devices. The only issue is that this is a tethered jailbreak which means you will have to boot it into a “jailbroken state” on every reboot.

So if you have an iOS device running iOS 4.2.1 check out our following guide on how to jailbreak the device using Redsn0w 0.9.6b4

[NOTE] Jailbreaking your device is not recommended by Apple, and this website will not be responsible for any loss of data or device malfunction which may occur from using this guide. Please proceed at your own risk.

[NOTE] Users who rely on a carrier unlock like ultrasn0w are advised to stay away from updating their software update until an update has been released. If you use a Mac and have access to the PwnAgeTool you can always create a custom firmware which you can install on your iDevice. A Sn0wBreeze update is also on it's way for Windows users. but for now stay away from the official firmware release if you rely on the unlock.

[NOTE] This guide only applies to the new devices like: iPhone 3GS (new bootrom), iPhone 4, iPod touch 2G (MC Model), iPod touch 3G and the iPod touch 4G. Old devices like iPhone 3GS (old bootrom), iPhone 3G, iPod touch 2G (Non-MC Model) and other devices can be jailbroken-untethered right now using this latest version of Redsn0w.

1. Download iOS 4.2.1. Download it according to your iOS device.
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2. Using iTunes 10.1, Update/Restore your iOS device to iOS 4.2.1. Use the IPSW file that you have downloaded in Step 1.
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3. Download Redsn0w 0.9.6b4 [WINDOWS | MAC]
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4. Run it and browse for the iOS 4.2.1 ipsw file. Click “Next >” to proceed with the jailbreaking process.
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5. Check the “Install Cydia” option to include Cydia in this firmware. You may also want to check other options mentioned there. Check them if you need them and click “Next” to proceed.|
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6. A window will appear instructing you to power off and plug in the iOS device. Follow the instructions and proceed by clicking “Next”.
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7. After clicking next, you need to grab your iOS device to enter DFU mode. Follow the on screen instructions to enter DFU mode. Precisely, hold “Power” and “Home” button for 10 seconds and then leave “Power” button but keep holding “Home” button for further 10 seconds or until the installation begins.
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8. It is up to Redsn0w now to do the rest. Wait while it jailbreaks your iOS device. When done, your iOS device will automatically reboot to the jailbroken iOS 4.2.1 firmware.
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   For iPhone 4, 3GS (New Bootrom), iPod touch 4G / 3G / 2G, and other newer devices:
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9. As the jailbreak is tethered, the device will loose the jailbroken state on every reboot. So to start the device in jailbroken state again, just select “Just boot tethered right now” option in Redsn0w.

You could alternately consider waiting for the untethered jailbreak to be released for iOS 4.2.1