We recommend making sure that automatic updates are enabled for your WordPress installation, or running a manual update. There’s a lot to gain, and a lot to lose if you don’t, since this release is mainly focused on security fixes.
Two of the corrected vulnerabilities are XSS (Cross Site Scripting), related to the processing of “shortcode” tags in versions 4.3 and earlier, and the user list page.
The other problem is a privilege escalation which in some cases allows an unauthorized user to post private items and mark them as “sticky”.
Although this version does not add any new features, it corrects a total of 26 bugs that exist in version 4.3.
In all, 64 files have been modified, with improvements to various aspects of the web interface of the world’s most popular CMS, as well as its backend functions.
So, log in to your admin console and get started!
Visit the official changelog for more details: https://codex.wordpress.org/Version_4.3.1