On PHP.net the project has posted about the release of the latest versions in the PHP 5.4.x and 5.3.x series - PHP 5.4.11 and 5.3.21:

The PHP development team announces the immediate availability of PHP 5.4.11 and PHP 5.3.21. These releases fix about 10 bugs. All users of PHP are encouraged to upgrade to PHP 5.4.

You can check out the Changelog if you're interested in what bugs were corrected by this release. The downloads are available via the main downloads page (or here for the Windows users out there).