The 3.0.0 system update was released on June 19, 2017. This update was released for all regions.
Security flaws fixed: unknown.
Change-log
This is the official changelog from Nintendo regarding this update:
Improvements Included in Version 3.0.0
- <see official site>
System Titles
It's unknown exactly what titles were updated.
OSS
The updated OSS includes a number of WebKit changes.