Quick take: Redsn0w 0.9.6b4 brings iOS 4.2.1 jailbreak support using the limera1n exploit, but most newer devices will be tethered.
We previously covered how to jailbreak iOS 4.2 using PwnageTool for Mac. Now the Dev Team has updated Redsn0w to version 0.9.6b4, adding support for iOS 4.2.1.
This version is based on Geohot’s limera1n bootrom exploit, which works across a wide range of iOS devices. The catch is that most newer devices will be limited to a tethered jailbreak.
Important: Jailbreaking is not supported by Apple and may void your warranty. Proceed at your own risk and make sure your data is backed up before continuing.
Unlock warning: If you rely on carrier unlock tools like ultrasn0w, avoid updating to official firmware until compatible updates are released. Consider using custom firmware tools like PwnageTool instead.
Supported devices
This guide applies to newer devices including:
- iPhone 4
- iPhone 3GS (new bootrom)
- iPod Touch 2G (MC model)
- iPod Touch 3G
- iPod Touch 4G
Jailbreak type
- Newer devices: Tethered jailbreak
- Older devices: Untethered jailbreak available
- Rebooting a tethered device requires reconnecting to Redsn0w
Step-by-step guide
- Download iOS 4.2.1 for your device from here.
- Use iTunes 10.1 to update or restore your device using the downloaded IPSW file.
- Download Redsn0w 0.9.6b4:
- Launch Redsn0w and browse for the iOS 4.2.1 IPSW file, then click Next.
- Select Install Cydia and any additional options you need, then proceed.
- Follow the on-screen instructions to power off and connect your device.
- Enter DFU mode:
- Hold Power + Home for 10 seconds
- Release Power but keep holding Home for another 10 seconds
- Wait while Redsn0w completes the jailbreak process. Your device will reboot automatically.
For tethered devices
If you are using a newer device, your jailbreak will be tethered.
What this means: Every time your device restarts, you must reconnect it to Redsn0w and select "Just boot tethered right now" to regain the jailbroken state.
Final thoughts
Redsn0w 0.9.6b4 is a solid option for getting iOS 4.2.1 jailbroken quickly, but the tethered limitation makes it less convenient for everyday use on newer hardware.
If you prefer a smoother experience, you may want to wait for a fully untethered jailbreak to be released.