In Pluck 4.7.16, an admin user can use the theme upload functionality at /admin.php?action=themeinstall to perform remote code execution.
https://github.com/SkDevilS/Pluck-Exploitation-by-skdevils
https://github.com/NUDTTAN91/CVE_CTF
https://github.com/kangvcar/Hacking-Write-ups
https://packetstormsecurity.com/files/166336/Pluck-CMS-4.7.16-Shell-Upload.html