Frontend File Manager < 18.3 - Unauthenticated Content Injection and Stored XSS

Description

The wpfm_edit_file_title_desc AJAX action of the plugin, available to unauthenticated users, did not check if users were editing their own post and was lacking a CSRF nonce as well. This could allow an unauthenticated user to update any post/page. Furthermore, by editing a post with the 'wpfm-files' type, this could also lead to Stored XSS issue as the file_title parameter is not properly sanitised