The NVD is the gold standard for security professionals. You can search for "PHP 5.6" to see the long history of CVEs (Common Vulnerabilities and Exposures).
: Addressed flaws that unauthenticated, remote attackers could exploit to compromise systems entirely. Post-Release Risks (EOL Status)
Upgrading to a newer PHP version is essential for maintaining the security and integrity of your website. Some of the benefits of upgrading include: