Ipswitch WS_FTP Server Manager before 6.1.1, and possibly other Ipswitch products, allows remote attackers to bypass authentication and read logs via a logLogout action to FTPLogServer/login.asp followed by a request to FTPLogServer/LogViewer.asp with the localhostnull account name.
When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct.