After many years being in the wild and widely deployed, the popular WPA2 protocol is compromised. The vulnerability allows a range of different attacks and it relates to the standard itself rather the respective implementation of the protocol. In fact, the “correct” implementation of the standard means that the underlying device is potentially vulnerable.
Users should be very cautious when using wifi access points (and public hotspots in particular), and as a first step are advised to use VPN.
Vendors are issuing patches, more information on the status can be found here.
Matt Green wrote a nice post on KRACK that’s worth a read for anyone interested in the root cause of KRACK