The December security release consists of 32 security updates in which 20 are listed as Critical and 12 are rated Important. The release consists of security updates for the following software:

Internet Explorer
Microsoft Edge
Microsoft Windows
Microsoft Office and Microsoft Services and Web Apps
Microsoft Exchange Server
Microsoft Malware Protection Engine

The updates address Remote Code Execution, Information Disclosure, "Defense in Depth" (Note: "Defense-in-Depth" is a fix that does not apply to an actively exploitable vulnerability but prevents future vulnerabilities caused by the same code when surrounding code changes expose the problem.), Security Feature Bypass, Spoofing and Denial of Service.

For more information about the updates released today, see Updates can be sorted by OS from the search box. Information about the update for Windows 10 is available at Windows 10 Update history.

Also see this month's Zero Day Initiative Zero Day Initiative The December 2017 Security Update Review by Dustin Childs in which he discusses several of the patches.

Release Notes
Windows 10 Update History