There is a zero-day exploit for Windows 8.1 and Windows 10 that can be used to crash a fully patched system. This attack exploits a vulnerability in Windows's SMB network file sharing protocol, which is used to share files and printers over a network and to handle authentication to those shared resources.
ComputerWorld provides some details about how the attack works but it looks like it's a fairly tame security risk. At the moment, there appears to be no evidence that it can be used for anything else than serving you a Blue Screen of Death (BSOD).
An attacker can exploit the vulnerability by tricking a Windows system to connect to a malicious SMB server which would then send specially crafted responses. There are a number of techniques to force such SMB connections and some require little or no user interaction, CERT/CC warned.
The good news is that there are no confirmed reports of successful arbitrary code execution through this vulnerability yet. However, if this is a memory corruption issue as described by CERT/CC, code execution might be a possibility.