iOS 11.2.1 (build 15C153) is an official Apple over-the-air update for the iPhone 5s (GSM), released on 2017-12-13T18:11:37Z. The update package is 315.45 MB. 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: 3ccfed1e8bb7361ec9f1e50ef4985ee4706f3860.zip.