For the latest information regarding the Meltdown and Spectre vulnerabilities see this document: A comprehensive guide to the Meltdown and Spectre vulnerabilities (regularly updated)
Microsoft released KB4058702 late the night of 1/3/18 (out of band) to address an Intel CPU firmware vulnerability. The patches released will be added to our patch definition update to be released later today, 1/4/18.
List of patches from Microsoft:
Important information on detection logic for the Intel 'Meltdown' security vulnerability
Current definitions in Patch and Compliance referencing Support for the Intel 'Meltdown' Security Vulnerability