https://arstechnica.com/gadgets/2017/10/apple-releases-macos-10-13-1-and-ios-11-1-with-a-krack-fix-and-new-emoji/

Today, Apple released iOS 11.1 and macOS High Sierra 10.13.1, which bring a notable security update, bug fixes, and a handful of other changes to modern iPhones, iPads, iPods, and Macs.

Critically, both software updates address the KRACK Wi-Fi vulnerability. It is a serious vulnerability in the WPA2 Wi-Fi security standard that allowed hostile actors to perform a key reinstallation and listen to Wi-Fi traffic for passwords and other personal data, among other things.