WordPress 4.0.1 is now available for download and upgrade.
This is a critical security release for all previous versions and we strongly encourage you to update your sites immediately.
Sites that support automatic background updates will be updated to WordPress 4.0.1 automatically. If you are still on WordPress 3.9.2, 3.8.4, or 3.7.4, you will be updated to 3.9.3, 3.8.5, or 3.7.5 to keep everything secure. (Older versions than 3.7.x are no longer supported so it is recommended to upgrade to the latest version)
WordPress versions 3.9.2 and earlier are affected by a critical cross-site scripting vulnerability, which could enable anonymous users to compromise a site. This issue does not affect version 4.0, but version 4.0.1 does address these eight security issues:
- Three cross-site scripting issues that a contributor or author could use to compromise a site.
- A cross-site request forgery that could be used to trick a user into changing their password.
- An issue that could lead to a denial of service when passwords are checked.
- Additional protections for server-side request forgery attacks when WordPress makes HTTP requests.
- An extremely unlikely hash collision could allow a user’s account to be compromised, that also required that they haven’t logged in since 2008.
- WordPress now invalidates the links in a password reset email if the user remembers their password, logs in, and changes their email address.
Version 4.0.1 also fixes 23 bugs with 4.0 and two hardening changes, including better validation of EXIF data that are extracted from uploaded photos.