With the launch Android 13 to Pixel 6 and 6a, Google posts interesting warning on the system image website: Once you flash Android 13, you can never go back to the old version. That’s still true for anyone wanting a fully functional phone, but now, Google has posted Android 12″developer support image” which will allow developers to restore their phones even after upgrading. The “developer” marking on the image means it’s not fully functional, but will be good enough for app testing.
The reason for Google’s one-way Android 13 update is a bootloader vulnerability. The bug is in the Pixel 6, 6 Pro, and 6a, so only those Pixels get a one-way update. Android 13 has a fix for a bootloader vulnerability, and to stop attackers from returning devices to work around patches, the company is triggering anti-rollback protection on the Pixel 6 and 6a. Anti-rollback protection blows a physical fuse inside the phone’s SoC. There are several of these fuses, and each OS version has a count of how many fuses to blow to expect. If the number is too high, it means that Google has marked that OS as insecure and out of date, and won’t boot anymore.
This “developer support image” is new territory for Google. The company says this Android 12 custom image fixes a bootloader bug and has an increased fuse counter so it can still boot. However, it will not get automatic updates, and it is not approved by the Compatibility Test Suite (CTS). CTS is a check that promises to be an unmodified, unrooted, and secure OS, and some online banking and gaming apps have to pass this check in order to work. You’ll also need to do a complete wipe of the device if you want to go back to normal “public” builds and updates.
If you’re still interested, Google has built Android 12 and 12L for the Pixel 6, 6 Pro, and 6a on developer.android.com.