The 2.3.0 system update was released on May 15, 2017. This update was released for all regions.
Security flaws fixed: unknown.
This is the official changelog from Nintendo regarding this update:
Improvements Included in Version 2.3.0
- General system stability improvements to enhance the user's experience
It's unknown exactly what titles were updated.
The browser was not updated.
"/nx/package2" in the FS was updated for both titles 0100000000000819 and 010000000000081A since 2.1.0. Unknown whether these have changed since 2.2.0. These (and the System Version Info title 0100000000000809) are the only packages known to be updated.