Weaknesses have been found in WPA2, a protocol that secures all modern protected Wi-Fi networks.
The attack (which has been nicknamed Krack) can allow an attacker to defeat encryption and view traffic which would normally be protected against viewing my an unauthorised user.
Official release and full write-up of Krack Attack is here
It is recommended to locate and apply firmware updates for your wireless devices, both Access Points, and also WiFi clients.