FTP Passive mode with misconfigured remote server and generic proxyenabled

[Franck Fuziol]

Hello,

I believe to have discovered a bug with the following:

If I access an ftp server in passive mode, that return its internal address instead of the public address after a PASV command, FileZilla with the “Use the server external IP address instead” option selected (under the Passive mode) does exactly that and the connection works (expected behavior).

When FileZilla is setup to use a FTP Generic Proxy (socks 5), that behavior seems to break and I can see in a wireshark trace, FileZilla requesting to the Proxy server to make a connection to the incorrect internal address instead of the external address.

Version of FileZilla: 3.10.0.1
Proxy server used : CCproxy 8.0 - ​http://www.youngzsoft.net/ccproxy/

Thank you,
Franck Fuziol | Director IT, Infrastructure Architecture| Seminole Gaming
phone: +1 954.327.7708; mobile: +1 954.520.0357

[Tim Kosse]

This is intentional and even required if the proxy endpoint is in the same LAN as the server.

As we do not have any information about the proxy endpoint, we cannot make any assumptions on the type of address the endpoint has. As such we need to trust the address returned by the server in the PASV reply is the correct one.