iOS 11.2.1 (build 15C153) is an official Apple over-the-air update for the iPhone 5s (GSM), released on 2017-12-13T18:11:26Z. The update package is 1.09 GB. This is a delta (partial) update that requires 10.1.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 99ef27332871f709702422e706dfa2afcb9e361a.zip.