Concretely, attackers can use this novel attack technique to read information that was previously assumed to be safely encrypted. This can be abused to steal sensitive information such as credit card numbers, passwords, chat messages, emails, photos, and so on. The attack works against all modern protected Wi-Fi networks. Depending on the network configuration, it is also possible to inject and manipulate data. For example, an attacker might be able to inject ransomware or other malware into websites.
His site: https://www.krackattacks.com
If you have a smartphone, laptop, or IoT device connected to a Wi-Fi network, the information you send over that network could be at risk.
Wi-Fi Protected Access (WPA) handshake traffic can be manipulated to induce nonce and session key reuse
Wi-Fi Protected Access (WPA, more commonly WPA2) handshake traffic can be manipulated to induce nonce and session key reuse, resulting in key reinstallation by a wireless access point (AP) or client. An attacker within range of an affected AP and client may leverage these vulnerabilities to conduct Key Reinstallation Attacks or "KRACK" attacks.