As is mentioned on PHP.net, the latest release of the 5.3.x series of the language has been released - PHP 5.3.7.
The PHP development team would like to announce the immediate availability of PHP 5.3.7. This release focuses on improving the stability of the PHP 5.3.x branch with over 90 bug fixes, some of which are security related.
Security fixes in this release include updates to crypt_blowfish() and a buffer overflow in crypt(). Enhancements include the fixes for several bugs including ones related to crashing due to internal errors, iterator fixes, sockets, ini settings and more. You can find the full list of changes in the Changelog for this release.
You can download the latest source from the downloads page or, for Windows users, the binaries.