The 5.5.3 version of PHP can be downloaded from Softpedia
PHP, an HTML-embedded scripting language with syntax borrowed from C, Java, and Perl, with a couple of unique PHP-specific features thrown in, has been updated to version 5.5.3.PHP 5.x includes a new OOP model based on the Zend Engine 2.0, a new extension for improved MySQL support, built-in native support for SQLite, and much more.
The previous PHP version, 5.5.2, had a lot of changes and improvements, including corrections for a buffer overflow and a lot more.
PHP 5.5.3, on the other hand, is a very small released and was made available only to fix one problem, related to the Openssl protocol (CVE-2013-4248 for anyone who is interested in reading more about the subject).
You can check out the official changelog in the readme file incorporated in the source package. Download PHP 5.5.3 right now from Softpedia.