The Simple:Press – WordPress Forum Plugin for WordPress is vulnerable to arbitrary file uploads due to missing file type validation in the ~/admin/resources/jscript/ajaxupload/sf-uploader.php file in versions up to, and including, 6.6.0. This makes it possible for attackers to upload arbitrary files on the affected sites server which may make remote code execution possible.
https://wpscan.com/vulnerability/27d4a8a5-9d81-4b42-92be-3f7d1ef22843
https://blog.nintechnet.com/wordpress-simplepress-plugin-fixed-critical-vulnerabilities/