Via PHP.net today there's an announcement about the latest release in the PHP 5.4.x series - PHP 5.4.21:

The PHP development team announces the immediate availability of PHP 5.4.21. About 10 bugs were fixed. All PHP 5.4 users are encouraged to upgrade to this version.

As always, you can download the latest source from the main downloads page or the Windows binaries from windows.php.net. Bug fixes in this release include updates to the CLI server, Datetime, DBA extension, IMAP and Filtering.