What happens when you make a socket() call in Windows? This presentation will briefly walk through the rather well documented winsock user mode framework before diving into the turmoil of ring 0. There is no map to guide us here. Our adventure will begin where MSDN ends and our first stop along the way is with an IOCTL to AFD.sys, or the awkwardly named ancillary function driver.
This driver is of particular interest because it is so widely used and yet most people that use it do not even know it exists. Nearly every Windows program managing sockets depends on this driver. Even more interesting is that the device created by AFD.sys is accessible from every sandbox Google Project Zero looked at. In fact, there isn't even support to restrict access to this device until Windows 8.1.
Staying true to Windows style AFD.sys is a complex driver with over 70 reachable IOCTL’s and support for everything from SAN to TCP. It is no wonder that this driver weighs in at 500KB. This complexity combined with accessibility breed a robust ring 0 attack surface. Current fuzzing efforts will also be shared in this presentation and the time we are done you should have a good idea of what happens when making a socket() call without having to spend hours in IDA to figure it out.