The remote web server uses a version of PHP that is affected by a Denial of Service (DoS) vulnerability.
Versions of PHP 5.6.x prior to 5.6.19 are vulnerable to a NULL pointer dereference flaw in the 'xsl_ext_function_php()' function in 'ext/xsl/xsltprocessor.c'. This may potentially allow a remote attacker to cause a crash. (OSVDB 135344)
Upgrade to PHP version 5.6.19 or later.