Jailbreak iPhone 4.2.1 for iPhone 4 & iPhone 3GS (Windows & Mac)

How to Jailbreak iPhone 4 & iPhone 3GS with iOS Version 4.2.1 Using Greenpois0n

Warning: Jailbreak at your own risk. Please exercise caution and read the comments, as these jailbreak instructions are not guaranteed to work.

To jailbreak other iPhone versions, see my in-depth iPhone Jailbreak instructions to find the right directions.

This tutorial contains jailbreak instructions for both Windows and Mac users, using Greenpois0n.

Windows & Mac Users


  1. iPhone 4 or iPhone 3GS
  2. Firmware: 4.2.1 (check your version in Settings » General » About)
  3. Download Greenpois0n RC5 b2 (Windows or Mac)

Jailbreak Instructions

1. With your iPhone plugged in via USB and iTunes off, open Greenpois0n.

2. Click Jailbreak and follow the on-screen instructions to put your iPhone in DFU mode.

3. Once the Jailbreak is finished, your iPhone will reboot. Open the new “Loader” app on your screen.

4. Then touch Cydia to install it.

5. If you would like to remove the Loader app, open Loader, go to Options and touch Remove Loader app.

Was your jailbreak successful? Please post questions and suggestions in the comments.

9 thoughts on “Jailbreak iPhone 4.2.1 for iPhone 4 & iPhone 3GS (Windows & Mac)”

  1. I have an IPhone 3Gs and it says that my modem firmware is 05.15.04 but my version is 4.2.1 which one tells me my ios?

  2. jailbreak was not success I have tried greenpois0n about 100 times. Everytime it gets to stage 3 and counts down to 4 it shuts off and stays off.


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