Microsoft released twelve (12) bulletins. Eight (8) bulletins are identified as Critical and the remaining four (4) are rated Important in severity. The updates address vulnerabilities in Microsoft Windows, Microsoft Edge, Internet Explorer, Microsoft .NET Framework, Microsoft Office, Skype for Business, Microsoft Lync Silverlight and Microsoft Silverlight.
Details about the CVEs can be found in the below-referenced TechNet Security Bulletin. If you are prioritizing updates, the most critical is MS15-0131.
Also released today is Microsoft Security Advisory 3123040 (https://technet.microsoft.com/en-us/library/security/3123040.aspx) which revokes a certificate for *.xboxlive.com where private keys were disclosed.
Microsoft Security Bulletin for December 2015 (https://technet.microsoft.com/library/security/ms15-dec)
Bulletin Summary:
https://technet.microsoft.com/en-us/library/security/ms15-dec.aspx
Critical (8 )
Cumulative Security Update for Internet Explorer (3116180)
http://go.microsoft.com/fwlink/?LinkId=699422
Cumulative Security Update for Microsoft Edge (3116184)
http://go.microsoft.com/fwlink/?LinkId=699426
Cumulative Security Update for JScript and VBScript to Address Remote Code Execution (3116178)
http://go.microsoft.com/fwlink/?LinkId=699421
Security Update for Microsoft Windows DNS to Address Remote Code Execution (3100465)
http://go.microsoft.com/fwlink/?LinkId=699414
Security Update for Microsoft Graphics Component to Address Remote Code Execution (3104503)
http://go.microsoft.com/fwlink/?LinkId=690559
Security Update for Silverlight to Address Remote Code Execution (3106614)
http://go.microsoft.com/fwlink/?LinkId=691214
Security Update for Microsoft Uniscribe to Address Remote Code Execution (3108670)
http://go.microsoft.com/fwlink/?LinkId=699420
Security Update for Microsoft Office to Address Remote Code Execution (3116111)
http://go.microsoft.com/fwlink/?LinkId=699410
Important [4]
Security Update for Microsoft Windows to Address Remote Code Execution (3116162)
http://go.microsoft.com/fwlink/?LinkId=699415
Security Update for Windows PGM to Address Elevation of Privilege (3116130)
http://go.microsoft.com/fwlink/?LinkId=699413
Security Update for Windows Media Center to Address Remote Code Execution (3108669)
http://go.microsoft.com/fwlink/?LinkId=699419
Security Update for Windows Kernel-Mode Drivers to Address Elevation of Privilege (3119075)
http://go.microsoft.com/fwlink/?LinkId=708239