WPS is a method for setting up a new wireless router for a home network and it includes a way for users to set up the network via an external or internal registrar. In this method, the standard requires a PIN to be used during the setup phase. The PIN often is printed somewhere on the wireless router or access point. The vulnerability discovered in WPS makes that PIN highly susceptible to brute force attempts.

via WiFi Protected Setup Flaw Can Lead to Compromise of Router PINs | threatpost.

“I noticed a few really bad design decisions which enable an efficient brute force attack, thus effectively breaking the security of pretty much all WPS-enabled Wi-Fi routers. As all of the of the more recent router models come with WPS enabled by default, this affects millions of devices worldwide,” Viehbock said in a blog post.