PHP object injection in the Ajax endpoint of the backend in ForkCMS below version 5.8.3 allows an authenticated remote user to execute malicious code.
https://www.ait.ac.at/themen/cyber-security/pentesting/security-advisories/ait-sa-20210215-04
https://tech.feedyourhead.at/content/ForkCMS-PHP-Object-Injection-CVE-2020-24036
http://seclists.org/fulldisclosure/2021/Mar/31
http://packetstormsecurity.com/files/161764/ForkCMS-PHP-Object-Injection.html