As is mentioned on the PHP.net website today, the latest release in the PHP 5.3.x series has been posted for download - PHP 5.3.1.
The PHP development team would like to announce the immediate availability of PHP 5.3.1. This release focuses on improving the stability of the PHP 5.3.x branch with over 100 bug fixes, some of which are security related. All users of PHP are encouraged to upgrade to this release.
Security updates in this release include a new max_file_uploads directive for the php.ini settings, the addition of some sanity checks on exif processing, correction of a safe_mode and open_basedir bypass and more. Check out the changelog for more information on what was updated and the release announcement for a full update.
You can download the source here and grab the Windows binaries here.