iOS 12.1.2 (build 16C101) is an official Apple over-the-air update for the iPhone 5s (GSM), released on 2018-12-17T21:06:27Z. The update package is 1.35 GB. This is a delta (partial) update that requires 11.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: c5cae9e83e0e6ff262579fd9ac50030103db500c.zip.