If you are asking about , you are looking at the final, now obsolete release of PHP 5.6 from January 10, 2019. If "5640" refers to a version string like 5.6.4.0 (an old alpha), that version has even more unpatched flaws. This post assumes the former, as it is the more common legacy system reference.
The PHP version 5.6.40 has several known vulnerabilities. Here are some resources and guidelines to help you understand and mitigate these issues: php version 5640 vulnerabilities link
This feature can be integrated into existing PHP applications, providing a robust security solution for PHP 5.6.40. Finding Information on PHP Vulnerabilities PHP 5