Last week, following the confirmation of SQL Server 2017 being generally available on Oct 2nd, Microsoft announced a major change to the way they will be releasing updates in future. They will no longer be producing Service Packs, instead relying on regular Cumulative Updates and ad-hoc General Distribution Releases. Full details can be found in this Release Services blog post.
The September security release consists of several updates for Windows systems, as well as for the following software:
Full details can be found at the Microsoft Security Response Center (MSRC).