The PHP development group has released several different versions of PHP for the 5.5.x, 5.6.x and 5.4.x series with a long list of security issues fixed in each one (fourteen in total):

The PHP development team announces the immediate availability of PHP [5.4.40, 5.6.8, 5.5.24]. 14 security-related bugs were fixed in this release, including CVE-2014-9709, CVE-2015-2301, CVE-2015-2783, CVE-2015-1352. All PHP 5.4 users are encouraged to upgrade to this version.

Other items were fixed besides the security issues, so check out the Changelog to see those few other fixes. It's highly recommended that you update your installations to these latest versions. You can grab the latest either from the downloads page (source) or Windows users can go to winodws.php.net.