iOS 12.3 (build 16F5155a) is an official Apple over-the-air update for the iPhone 5s (GSM), released on 2019-05-07T17:04:20Z. The update package is 393.32 MB. This is a delta (partial) update that requires 12.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 1aaba0e14f734e94e56605a2529e85b044a96e9f.zip.