Here is the step by step guide:
- Download Greenpois0n: Download for Mac and Windows
- Open GreenPois0n and click on jailbreak button
- Follow the onscreen instructions to put your iDevice in DFU mode. Once it is complete, Greenpois0n will start jailbreaking your device.
Note: You’ll get some errors initially but it should continue in a few seconds. If not, then start the whole process again.
- Your iDevice should be jailbroken. There should be a “loader” icon on your homescreen. Open it and install cydia.
Thats it. Enjoy the untethered jailbroken iPhone running iOS 4.2.6.