An oversight by Apple caused an old security bug to be reintroduced with iOS 12.4. While the bug had been patched in iOS 12.3, the exploit is present in the latest operating system from Apple and can be used for jailbreaking on compatible devices. On the flip side, the security hole presents new risks; the bug can be used by malicious parties to hack into an iPhone or iPad running 12.4.
https://www.notebookcheck.net/Apple-accidentally-rolls-back-security-patch-in-iOS-12-4-update-making-jailbreaking-possible.431179.0.html
Wonderful, now's probably the best time to upgrade my old iPP to a signed firmware.