To apply this cumulative update package, you must be running SQL Server 2014 SP1. So it is pertinent for versions 12.0.4100.1 - 12.0.4436.0. Note you cannot apply this patch if you do not have SP1 installed.
The build number of the cumulative update package is 12.0.4439.1. You may have to restart the computer after you apply this cumulative update package. The cumulative update package updates only those components currently installed.
This update contains 21 updates. As usual, make sure you deploy Cumulative Updates in test environments before deploying straight to production and that you apply the most recent build that you apply the most recent build.
This Cumulative Update contains a change that Aaron Bertrand wrote about here, and a very bad idea it is to have changed @@VERSION. You need to review options 2 and 4 of this guide to determine SQL Server version. What’s weird is that this was also in CU4… so not sure if it is included or not. It’s a potentially major breaking change, so proceed with caution.
The full info can be read on the SQL Sentry site, which covers the updates for both SP1 and RTM releases in SQL Server than I do in my bulletins.