Provide references for CVE-2021-4387.
Where can I find more information about CVE-2021-4387?
References are available at: https://www.wordfence.com/threat-intel/vulnerabilities/id/2645899c-2b6b-48bd-8f33-2a837a951c5e?source=cve, https://blog.nintechnet.com/25-wordpress-plugins-vulnerable-to-csrf-attacks/, https://blog.nintechnet.com/more-wordpress-plugins-and-themes-vulnerable-to-csrf-attacks/, https://blog.nintechnet.com/multiple-wordpress-plugins-fixed-csrf-vulnerabilities-part-3/, https://blog.nintechnet.com/multiple-wordpress-plugins-fixed-csrf-vulnerabilities-part-2/, https://blog.nintechnet.com/multiple-wordpress-plugins-fixed-csrf-vulnerabilities-part-1/, https://blog.nintechnet.com/multiple-wordpress-plugins-fixed-csrf-vulnerabilities-part-5/, https://blog.nintechnet.com/multiple-wordpress-plugins-fixed-csrf-vulnerabilities-part-4/, https://plugins.trac.wordpress.org/browser/opal-estate/trunk/inc/ajax-functions.php#L177.