iOS 11.2.1 (build 15C153) is an official Apple over-the-air update for the iPhone 7 (GSM), released on 2017-12-13T18:14:55Z. The update package is 57.46 MB. This is a delta (partial) update that requires 11.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 68735ab243da494f10f95d1d42cc7179c0daabfb.zip.