SFTP with ProxyCommand throwing Error reading SSH protocol banner

Hi all

trying to run the following and i cant seem to get it working

Its accessing an sftp server behind a bastion

using Version: 2.10.3

>>> with paramiko.proxy.ProxyCommand(f'sshpass -p {SBC_PASSWORD} ssh -o "ProxyJump 10.10.10.1" admin@20.20.20.1') as pc:
...     with paramiko.client.SSHClient() as client:
...         client.connect('100.71.133.13', sock=pc, banner_timeout=60)
...         sftp = client.open_sftp()
...         o = sftp.listdir()
...         print(o.readline())
... 

DEBUG:paramiko.transport:starting thread (client mode): 0xe45bed0
DEBUG:paramiko.transport:Local version/idstring: SSH-2.0-paramiko_2.10.3
DEBUG:paramiko.transport:Banner: vtc-us-east-...f87cf77-esbc# SSH-2.0-paramiko_2.10.3
DEBUG:paramiko.transport:Banner: % command not found
DEBUG:paramiko.transport:Banner: vtc-us-east-...f87cf77-esbc# 
ERROR:paramiko.transport:Exception (client): Error reading SSH protocol banner
ERROR:paramiko.transport:Traceback (most recent call last):
ERROR:paramiko.transport:  File "/home/<redacted>/.local/lib/python3.7/site-packages/paramiko/transport.py", line 2270, in _check_banner
ERROR:paramiko.transport:    buf = self.packetizer.readline(timeout)
ERROR:paramiko.transport:  File "/home/<redacted>/.local/lib/python3.7/site-packages/paramiko/packet.py", line 380, in readline
ERROR:paramiko.transport:    buf += self._read_timeout(timeout)
ERROR:paramiko.transport:  File "/home/<redacted>/.local/lib/python3.7/site-packages/paramiko/packet.py", line 622, in _read_timeout
ERROR:paramiko.transport:    raise socket.timeout()
ERROR:paramiko.transport:socket.timeout
ERROR:paramiko.transport:
ERROR:paramiko.transport:During handling of the above exception, another exception occurred:
ERROR:paramiko.transport:
ERROR:paramiko.transport:Traceback (most recent call last):
ERROR:paramiko.transport:  File "/home/<redacted>/.local/lib/python3.7/site-packages/paramiko/transport.py", line 2093, in run
ERROR:paramiko.transport:    self._check_banner()
ERROR:paramiko.transport:  File "/home/<redacted>/.local/lib/python3.7/site-packages/paramiko/transport.py", line 2275, in _check_banner
ERROR:paramiko.transport:    "Error reading SSH protocol banner" + str(e)
ERROR:paramiko.transport:paramiko.ssh_exception.SSHException: Error reading SSH protocol banner
ERROR:paramiko.transport:
Traceback (most recent call last):
  File "/home/<redacted>/.local/lib/python3.7/site-packages/paramiko/transport.py", line 2270, in _check_banner
    buf = self.packetizer.readline(timeout)
  File "/home/<redacted>/.local/lib/python3.7/site-packages/paramiko/packet.py", line 380, in readline
    buf += self._read_timeout(timeout)
  File "/home/<redacted>/.local/lib/python3.7/site-packages/paramiko/packet.py", line 622, in _read_timeout
    raise socket.timeout()
socket.timeout

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 3, in <module>
  File "/home/<redacted>/.local/lib/python3.7/site-packages/paramiko/client.py", line 406, in connect
    t.start_client(timeout=timeout)
  File "/home/<redacted>/.local/lib/python3.7/site-packages/paramiko/transport.py", line 698, in start_client
    raise e
  File "/home/<redacted>/.local/lib/python3.7/site-packages/paramiko/transport.py", line 2093, in run
    self._check_banner()
  File "/home/<redacted>/.local/lib/python3.7/site-packages/paramiko/transport.py", line 2275, in _check_banner
    "Error reading SSH protocol banner" + str(e)
paramiko.ssh_exception.SSHException: Error reading SSH protocol banner

Start with paramiko.proxy.ProxyCommand and SSHClient.connect, then inspect the logged Transport._check_banner and Packetizer.readline paths. Reproduce the reported ProxyJump setup with Paramiko 2.10.3; the issue is only complete once the cause of the banner timeout is established and an appropriate regression test or documented resolution is identified.