Disclaimer
- I am not responsible if anything goes wrong with the downgrade. In a rare case that it ever goes wrong, put the device into DFU mode and just click restore in iTunes.
- There will not be a jailbreak guide, as most versions can be jailbroken untethered with Redsn0w.
Required Tools
- MacOS computer running macOS High Sierra
- An iPhone 3G[S]
- A 30-pin USB cable
- Your desired downgrade firmware
- LibUSB
- Homebrew
- Ipwndfu
- iTunes 11
Setting Thing Up - macOS
- On your macOS device, upgrade to the latest version of Xcode by upgrading through the App Store.
- To install Homebrew, paste this into a terminal window: /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install.sh)"
- Once HomeBrew finishes downloading, you'll want to install LibUSB. To do this, run HOMEBREW_NO_AUTO_UPDATE=1 brew install libusb
- After LibUSB finishes downloading, you'll need to install Ipwndfu. To do this, go to this link here, and click Code>Download Zip
- Extract the Zip file and drag the zip file to your desktop. Now, go to this website and download the attached .img3 iBSS. Once downloaded, drag the iBSS image file into the Ipwndfu folder.
- Download iTunes 11 from Apple
- Once downloaded, do not open iTunes, as we will be removing our current installation of iTunes and downgrading it.
Downgrading iTunes
- Boot into macOS Recovery mode by shutting down your Mac and booting it up whilst holding ⌘R.
- Log in, open terminal, and run csrutil disable
- Reboot back into the normal OS and open a terminal window.
- In the terminal window, run cd /Applications/, then run sudo rm -rf iTunes.app/ and enter your login password.
- Run the iTunes 11 installer.
Downgrading the phone
- Connect your iPhone 3G[S] to your computer.
- Put it in DFU mode by holding both the home and power buttons for 8 seconds, releasing the power and only hold the home for another 8 seconds.
- Open up a terminal window.
- Write cd <Drag iPwnDFU folder into terminal window>
- Press Enter or Return
- Run ./ipwndfu -p
- Wait for the confirmation that your device is in pwned DFU mode, and open up iTunes. Do not close the terminal window.
- Restore by holding option or alt whilst clicking the restore button and selecting your ipsw for the firmware you wish to downgrade to.
- Once the restore has finished, do not unplug your phone.
- Head back to the terminal window and run ./ipwndfu -p again.
- Once you get the confirmation that it is in pwned DFU mode again, finally run ./ipwndfu -x
- Your iPhone 3G[S] should now be booting up untethered to your desired firmware.