What does krack stand for? Key Reinstallation Attack
krack attack affects all modern WPA2 implementations, and is particularly dangerous on Android 6+/Linux – you can force a WiFi connection to use a session key consisting of zeroes alone … And that’s all because these platforms wanted to be more secure, but that’s a bit further.

Depending on the security model you use, you can: Decrypt the communication, spoof the communication (impersonate the sending packets), inject the packets.