This maintenance release fixes a severe bug in 4.9.3, which will cause sites that support automatic background updates to fail to update automatically, and will require action from you (or your host) for it to be updated to 4.9.4.
Four years ago with WordPress 3.7, we added the ability for WordPress to self-update, keeping your website secure and bug-free, even when you weren’t available to do it yourself. For four years it’s helped keep millions of installs updated with very few issues over that time. Unfortunately yesterdays 4.9.3 release contained a severe bug which was only discovered after release. The bug will cause WordPress to encounter an error when it attempts to update itself to WordPress 4.9.4, and will require an update to be performed through the WordPress dashboard or hosts update tools.
WordPress managed hosting companies who install updates automatically for their customers can install the update as normal, and we’ll be working with other hosts to ensure that as many customers of theirs who can be automatically updated to WordPress 4.9.4 can be.
For more technical details of the issue, we’ve posted on our Core Development blog. For a full list of changes, consult the list of tickets.
Download WordPress 4.9.4 or visit Dashboard → Updates and click “Update Now.”