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in .NET FTP by (158k points)

In the debug log, the connection is shown as working, but when a file is transferred or a directory is listed, the connection is closed by the server. This only happens from version 9.7.0 or later.

DEBUG [SocketController] 4 nov 2020 14:30:49.582 : FTPConnection.2 OnReceive closing (size == 0)
DEBUG [SocketController] 4 nov 2020 14:30:49.584 : FTPConnection.2 CloseConnection(e=null)
DEBUG [SocketController] 4 nov 2020 14:30:49.584 : FTPConnection.2 Shut down socket
DEBUG [SocketController] 4 nov 2020 14:30:49.585 : FTPConnection.2 Closed socket

1 Answer

0 votes
by (158k points)
Best answer

This is a problem with Filezilla server, and it is because Filezilla server does not support the extended master secret feature in TLS. This feature makes connections more secure. 

If a server does not support the extended master secret and the client does, the RFC says the client should not resume connections. But Fiezilla server has a setting that says if a data connection (used to list directories or transfer files) does not resume, then terminate the connection. 

The Filezilla log shows it happening:

450 TLS session of data connection has not resumed or the session does not match the control connection

To fix the problem,go to FTP over TLS settings in the Filezilla server options, and uncheck "Require TLS session resumption on data connection when using PROT P".

by (130 points)
I think I have the same question about this. I find out the log that I think key point, as follow:
DEBUG:  Resumed session does not support extended_master_secret - not resuming
DEBUG :  Handshake started
DEBUG :  Waiting for handshake completion
DEBUG :  Waiting for handshake to complete (timeout=30000ms)
DEBUG : FTPConnection.25 Processing hello
DEBUG : FTPConnection.25 Remote SSL version: 3.3
DEBUG : FTPConnection.25 ProcessMessages(Handshake)
DEBUG : FTPConnection.25 Handshake Message: ServerHello
DEBUG : FTPConnection.25 Cipher suite selected: ECDHE_RSA_AES_128_SHA
DEBUG : FTPConnection.25 Extension len=8
DEBUG : FTPConnection.25 Extension type ECPointFormats
Excuse me, How could we resolve this problem by changing my program? I must connect to different FTPS Server, and I don't know what kinds of those?
Could we close to use " extended master secret"? or
Could we close this command by setting parameters in edtFTPnetPro API??
by (6.2k points)
This feature has been added to Version 9.9.0. Please update to this version.
by (130 points)
Great! Thanks!