MediaWiki developers: http://www.php.net/archive/2014.php#id2014-04-02-1 (02 Apr 2014):
The PHP development team announces the immediate availability of PHP 5.5.11. Several bugs were fixed in this release, some bundled libraries updated and a security issue has been fixed : CVE-2013-7345. We recommend all PHP 5.5 users to upgrade to this version.