In order to patch the PDF exploit, an exploit that allowed JailbreakMe to jailbreak iPhones on firmware version 4.0.1 and also posed major security risks, Apple recently released iOS 4.0.2. While iPhone 4 and iPhone 3GS users who upgraded to 4.0.2 may be out of luck for the time being, the iPhone 3G and iPhone 2G (the original iPhone) can still upgrade to the newest iOS and be jailbroken with Redsn0w. Instructions follow:
Step 1: Download the correct iOS 4.0.2 version for your iPhone from Apple and update your phone to this firmware via iTunes.
Step 2: Download iOS 4.0 firmware for your iPhone and the latest version of Redsn0w (can be found with a simple Google search) which is version 0.9.5b5-5. Run Redsn0w and when prompted to select an IPSW, select the iOS 4.0 firmware you just downloaded (NOT 4.0.2).
Step 3: Select the Install Cydia check box in Redsn0w and click Next. At this point you’ll need to make sure your iPhone is plugged in to your computer and turned off. Click Next again and be prepared to follow step 4.
Step 4: After clicking Next at the previous screen, Redsn0w will give a series of instructions on how to put your device into DFU mode. When this screen appears, follow the instructions which will involve pressing and releasing the home and power buttons and various intervals. Be sure to follow the instructions precisely as they are given.
The rest of the process is done automatically by Redsn0w and requires no user input. Once Redsn0w finishes this process, your phone will be jailbroken and should restart automatically. Check under general settings and you will find you are on iOS 4.0.2 and jailbroken!
Those who also need their iPhone unlocked can do so by downloading the latest Ultrasn0w from Cydia. The 4.0.2 update did not change the baseband and therefore the Ultrasn0w carrier unlock still works as it did before. Also, you may want to check out some of the top 5 apps for jailbroken iPhones