Researchers have disclosed a serious weakness in the WPA2 protocol that allows attackers within range of vulnerable device or access point to intercept passwords, e-mails, and other data presumed to be encrypted, and in some cases, to inject ransomware or other malicious content into a website a client is visiting.

The proof-of-concept exploit is called KRACK, short for Key Reinstallation Attacks. The research has been a closely guarded secret for weeks ahead of a coordinated disclosure that was scheduled for 8am Monday, East Coast time. A website disclosing the vulnerability said it affects the core WPA2 protocol itself and is effective against devices running Android, Linux, and OpenBSD, and to a lesser extent macOS and Windows, as well as MediaTek Linksys, and other types of devices. The site warned that attackers can exploit the flaw to decrypt a wealth of sensitive data that's normally encrypted by the nearly ubiquitous Wi-Fi encryption protocol.

"This can be abused to steal sensitive information such as credit card numbers, passwords, chat messages, emails, photos, and so on," researcher Mathy Vanhoef, of the Katholieke Universiteit Leuven in Belgium wrote. "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."
Read more at Ars Technica

TL;DR WiFi security is broken, but a firmware patch on your router can fix it. Just hope for an update in the next few weeks.