Pluck CMS through 4.7.21 restricts dangerous file uploads in its admin file-management feature using a fixed blacklist in data/inc/files.php ('.php','php3','php4','php5','php6','php7','phtml','.phtm','.pht','.ph3','.ph4','.ph5','.asp','.cgi','.phar'), checked against the last 4-5 characters of the filename. The blacklist omits the '.php8' extension. An authenticated administrator can upload a file named e.g. shell.php8, which is stored unmodified and, on servers running PHP 8.x, is executed as PHP by the web server, resulting in remote code execution.
Analyzing vulnerability vectors…