Version 4.8.4

From the WordPress 4.9.1 release post: WordPress versions 4.9 and earlier are affected by four security issues which could potentially be exploited as part of a multi-vector attack. As part of the core team’s ongoing commitment to security hardening, the following fixes have been implemented in 4.9.1:

1. Use a properly generated hash for the newbloguser key instead of a determinate substring.
2. Add escaping to the language attributes used on html elements.
3. Ensure the attributes of enclosures are correctly escaped in RSS and Atom feeds.
4. Remove the ability to upload JavaScript files for users who do not have the unfiltered_html capability.

List of Files Revised

wp-admin/about.php 
wp-admin/user-new.php 
wp-includes/feed.php 
wp-includes/functions.php 
wp-includes/general-template.php 
wp-includes/version.php 
wp-includes/wp-db.php