The developers of WordPress.org have just released the updated version WordPress 4.9.2 (Billy Tipton) to fix some security holes.
The change log begins by stating that all older versions of WordPress are affected by a vulnerability XSS in the Flash fallback files of MediaElement 4.x, a library included in the WordPress 4.9.
In addition to the above security issue, the new WorPress 4.9.2 contains other 21 bug fixes that you can see in official announcement.
Of course, as with any other update regardless of vendor, immediate is recommended upgrade. You can perform a fresh installation with the package, or upgrade automatically through the admin panel of the web application.
https://wordpress.org/download/
