Microsoft has published a web site containing the latest updates for all supported versions of Microsoft SQL Server, including SQL Server 2008 up to SQL Server 2017.
The latest patches, released January 2018, include fixes for the Spectre and Meltdown vulnerabilities. Details on these updates, as well as updates to Windows, can be found in the following Microsoft Security Advisory.
We recommend updating all installing of Microsoft SQL Server to include these patches. For older versions of Microsoft SQL Server, we recommend upgrading as soon as possible.