Ian Beer, a Google security researcher who works for the Project Zero team, has released a kernel exploit that works could be the foundation for a future iOS 12 jailbreak. According to Beer, the exploit has already fixed in the latest iOS 12.1.3 update, meaning it should work on all iOS devices running iOS 12.1.2 or below.
Since iOS 12.1.3 was released by Apple a couple weeks ago, and the company plans to release iOS 12.1.4 to fix the FaceTime bug, Apple is likely to stop signing iOS 12.1.2 shortly after that. and it could come sooner than you expected as the exploit has been released. We recommend that those interested in the jailbreak for iOS 12 to keep a device running on iOS 12.1.2 or earlier version.
However, as Apple announced today that it will release a software update next week to address the FaceTime bug. it proposes that the Group FaceTime feature on the iOS 12.1 to iOS 12.1.3 system will be permanently blocked. If you need to use Group FaceTime, then we advise you to not to downgrade to iOS 12.1.2 or below, otherwise, users must update their devices to iOS 12.1.4 to use the feature.