Updated: The Sony Xperia X and X Compact have also started getting the September security patch. The update - which is currently rolling out in several markets across the globe - bumps the build number from 34.3.A.0.217 to version 34.3.A.0.228.
Original story follows:
There's currently no information on what other changes (if any) the update includes. The roll out is currently limited to a few regions, although it's expected to expand in the near future.
Aside from Sony, Google and Nokia have also pushed out the latest security patch to some of their devices.