On the main PHP.net site they've officially announced the release of the latest versions in the 5.6.x and 5.5.x series: PHP 5.6.18 and PHP 5.5.32.

The PHP development team announces the immediate availability of PHP [5.5.32 and 5.6.18]. This is a security release. Several security bugs were fixed in this release. All PHP [5.5 and 5.6] users are encouraged to upgrade to this version.

As always you can download this latest release from either the main downloads page or from windows.php.net for the Windows binaries. If you'd like to see exactly what was fixed in these releases, check out the full Changelog.