In WS_FTP Server versions prior to 8.7.6 and 8.8.4, an unrestricted file upload flaw has been identified. An authenticated Ad Hoc Transfer user has the ability to craft an API call which allows them to upload a file to a specified location on the underlying operating system hosting the WS_FTP Server application.
https://www.progress.com/ws_ftp
https://community.progress.com/s/article/WS-FTP-Server-Service-Pack-November-2023