SFTP v4.9/v5.0 Protocol Differences

[Stan Wong]

I have a problem with an embedded system which is acting as a SFTP client.  I get different repsonses from the SFTP server depending on if it is OpenSSH version 5.0 or versions 4.x.  The SFTP client speaks SFTP protocol version 3.

With OpenSSH version 5.0, the embedded SFTP client panics because it receives something it thinks it shouldn't get at the start of a data transfer from the server.  I have traced it to a section of code where it is processing incoming packets and it doesn't know what to do with what it has received.  The code comment at this section is "Message an sftp client should never receive".  I haven't been able to do a data dump at this point, yet, to find out exactly what it is receiving.

I do not have a problem if I use OpenSSH 4.9 or earlier.  Can anyone tell me what might have changed in the SFTP protocol section from v4.9 to v5.0?

I have tested with the following SFTP servers:

COPSSH (Windows, Cygwin, OpenSSH)
  OpenSSH 5.0p1-1  (doesn't work)
  OpenSSH 4.7p1
  OpenSSH 4.5p1
  
Fedora 7
  OpenSSH 4.5p1-6
  
I have searched the archives and Bugzilla but don't find any reports similar to my problem.  If this has been reported, can anyone can point me to the post or Bugzilla entry?  If anyone has information or ideas I'd appreciate those, too.  Thanks.