SFTP protocol violation: Invalid message number

I just upgraded to WinSCP 6.1 and now I'm getting the following error for a couple of my SFTP sites.

SFTP protocol violation: Invalid message number

Is there something I can do to fix this problem. As information, I've connected to the problematic sites with another program successfully.

Thank you

I am also getting the same error message when connecting to one server. This started right after upgrading to 6.1
I tried changing the Preferred SFTP protocol version to 5, as suggested, but still got the error.
Log file is attached.

If I use FileZilla, I am able to connect successfully – but I would rather use WinSCP.
Are there other workarounds available?
Thanks

Thanks both. Can you please post session log file on Debug 2 level? A log file from a working session from an older version of WinSCP might be useful too.

Thanks Martin. I'm attaching what I hope is the right log file for you.
-Sam

@ssstevens: Thanks. But can you please post also log of a working session from the previous version? You can download it from
https://sourceforge.net/projects/winscp/files/WinSCP/

Hi Martin,
I installed an older version (didn't know I could downgrade so easily) and the problem went away. Here is the level 2 log file.
Thank you for being so responsive!

Thanks. Imo, it's clearly a bug on the server side. The server "supports" vendor-id SFTP extension. It first sends its own nonsense vendor information:

. Server software: ${pom.artifactId} ${pom.version} (0) by ${pom.groupId}

And when WinSCP sends its own vendor information (that's new in WinSCP 6.1), the server just fails totally.

For a start, can you try decreasing SFTP version to 3 (or even lower)? It might prevent the server from sending its vendor information, what would in turn prevent WinSCP from sending its.
https://winscp.net/eng/docs/ui_login_sftp

If you have means for contacting the server vendor, please report the problem to them.

Thank you for figuring this out, Martin. I will contact the server vendor.

Let us know what their response was.

Hi,

I also get the message:

SFTP protocol violation: Invalid message number 8 (expected 200).

The numbers change, but the message stays the same.
I can't change anything on the server side because "Everything is fine with our server. It must be a problem with your client"...
FileZilla works fine, but we need a way to have the transfer scripted because of reasons ;-)

I've attached the log of a failed attempt.
Maybe someone can see what the issue is?
I've tried reducing the SFTP-version but the error stays the same (if I go down to 2, I get the messsage that I should use 3,4,5 or 6).

Thanks for the log.
The server supports vendor-id SFTP extension. So WinSCP uses the extension to provide the server with its information using SSH_FXP_EXTENDED request (with "sequence number" 200). To this, the server should respond with SSH_FXP_EXTENDED_REPLY response with the same sequence number. (Or with an error using SSH_FXP_STATUS response, though that is not expected in this case). Instead, the server "responds" with SSH_FXP_EXTENDED message with sequence number 8. This is totally wrong:

• SSH_FXP_EXTENDED is not a valid response to SSH_FXP_EXTENDED request.
  
• SSH_FXP_EXTENDED is a request message. It can only ever be sent by the client, never by the server.
  
• The "response" uses wrong sequence number. In that session, WinSCP didn't sent any request with sequence number 8.
  

It's irrelevant that FileZilla "works", as FileZilla does not support the vendor-id extension. So it does not trigger the bug in the server.

Hi, thanks for the quick analysis.

Is there anything I can do on my side to get it to work?
Or does the Server-side need to change something?

Thanks again for the quick reply.

@EDISean: Yes, the server needs to be fixed.
I may try to implement a workaround.

that would be awesome.
I've relayed your information to the server guys, but got no reply.
Oh well....

I have added this issue to the tracker:
Bug 2222 – Allow disabling SFTP extension use

I'm sending you an email with a development version of WinSCP to the address you have used to register on this forum.

Hi,

I've already answered via email, but just to let every other person with the same problem know: IT WORKED!!!

Is there a timeline when (or if) it will be implemented in the release-version of WinSCP?

@EDISean: A beta version will be released in few weeks.