Apple stops the possibility of signing versions before iOS 12.4, this being the latest version currently available for iOS 12. If you have iOS 12.3.1 or iOS 12.3.2 firmware and have not installed it on one of your devices, you can now erase it. Apple reason behind this is none other than protecting the security of its users.
Apple servers released iOS 12.4 on July 22, adding new features. The most important change was to focus on solving various security flaws that recently been detected through Google’s Project Zero program, and that allowed malicious code to run on the iPhone through an application exploit Messages.
Currently, Apple has already released the fourth beta of iOS 13 for both developers and public beta testers. We can say with almost certainty that iOS 12.4 will be the last update that this version of iOS will receive unless some new security flaws are detected.
According to the latest official iOS adoption data, 87% of compatible devices, sold in the last 4 years, are running iOS 12 in one of the different versions that Apple has launched to the market since its arrival in the market.
If you are waiting for any movement related to the jailbreak in iOS 12.3, at the moment, everything seems to indicate that there is nothing about it, so if you were waiting for it to do it on your usual device, it is probably convenient for you to update your device to iOS 12.4 to correct the security flaws found by Google.