On January 4, 2018, Microsoft released SQL Server 2017 CU3, which is Build 14.0.3015.40. By my count, this CU has sixteen public hotfixes, many of which are for the SQL Engine or SQL performance. There are also some new manageability and programmability features that have been added, such as support for the MAXDOP option for CREATE STATISTICS and UPDATE STATISTICS.
In addition, Microsoft has included the security fixes from the January 3 SQL Server security update in this Cumulative Update. Microsoft has very detailed guidance on how this may affect SQL Server here. One important item to note is that SQL Server 2017 CU3 may have been offered and deployed as an important update by Microsoft Update, depending on how your Microsoft Update settings are configured or whether you are using WSUS.
Since SQL Server 2017 won’t be using Service Packs as part of its servicing mechanism, you will need to start testing and deploying Cumulative Updates on a schedule that makes sense for your organization.
As always, I think it is a good idea to make an effort to stay current on Cumulative Updates, as does Microsoft.