- The following guide to root the Samsung Galaxy S3 running on Android 4.1.2 is based on JZO54K.I9300XXELLC firmware. You do not need to be running that firmware; however, you should wait a while if your device has just been updated to a new software update. It takes a while for the new recovery.img files to make their way to Chainfire who has to then update his files. Rooting too soon after an update can lead to a device that does not boot up.
BEFORE WE BEGIN
- Download and install the Samsung USB Drivers  for mobiles phones from our USB Drivers page. make sure you install that new driver before you start the guide or else it might not work for you. A Windows computer relies on your drivers to help the device, the computer and the programs that are running on that computer all communicate with each other properly.
- You are voiding the warranty by rooting the Samsung Galaxy S3 smartphone using the CF-Auto-Root tool. You can unroot the device by flashing the stock ROM and the Samsung Galaxy S3 warranty will start working again. There are no limits as to how many times you can continue rooting and unrooting for the warranty to continue working.
HOW TO ROOT SAMSUNG GALAXY S3 ON ANDROID 4.1.2
- Download the updated CF-Auto-Root tool for the GT-I9300 on 4.1.2 from this link .
- Download the Odin 1.85 for the S3 device from this link .
- Right-click over the files when they are on the desktop of your computer and pick the “Extract here” option from the menu.
- Run the Odin flash tool by clicking over the Odin executable file.
- Hold the Power button and choose “Switch Off” from the Device Options menu.
- Boot the Samsung Galaxy S3 in download mode by pressing and holding the Home + Power and Volume Down buttons together.
- Keep holding the three buttons until you can see the Volume Up option from the display on your smartphone. Release the three buttons and press the Volume Up button at this point.
- Connect the Samsung Galaxy S3 smartphone to the computer with the USB cable.
- Click the PDA button and browse the desktop of the tar.md5 file you extracted earlier.
- Click the Start button and the Odin flash tool will flash that tar.md5 file on your Samsung Galaxy S3.
- Wait for the Odin app on the computer to give you the pass message.
The Samsung Galaxy S3 smartphone should automatically reboots if things to go to plan. The rebooting needs to happen for the rooting to work because it’s going to reboot your device into recovery mode. Those who do not see their device reboot in recovery mode by apply that manually by holding the Volume Down + Home + Power buttons during a boot only.