The remote web server uses a version of PHP that is affected by a use-after-free vulnerability.
Versions of PHP 5.6.x prior to 5.6.13 are vulnerable to a use-after-free error in the 'gmp_unserialize()' function in 'ext/gmp/gmp.c.' The issue is triggered as user-supplied input is not properly sanitized. This may allow a remote attacker to dereference already freed memory and potentially execute arbitrary code. (OSVDB 126960)
Upgrade to PHP 5.6.13, or later.