Unhandled ValueError during authentication

[ecbftw]

Configuration

impacket version: 0.12.0
Python version: 3.10
Target OS: Ubuntu 22.04

Debug Output With Command String

Sometimes when authenticating to specific devices, the following traceback is thrown:

>   File "/usr/local/lib/python3.10/dist-packages/impacket/smbconnection.py", line 278, in login
>     return self._SMBConnection.login(user, password, domain, lmhash, nthash, ntlmFallback)
>   File "/usr/local/lib/python3.10/dist-packages/impacket/smb.py", line 3504, in login
>     self.login_extended(user, password, domain, lmhash, nthash, use_ntlmv2 = True)
>   File "/usr/local/lib/python3.10/dist-packages/impacket/smb.py", line 3368, in login_extended
>     sessionData.fromString(sessionResponse['Data'])
>   File "/usr/local/lib/python3.10/dist-packages/impacket/structure.py", line 149, in fromString
>     size = self.calcUnpackSize(field[1], data, field[0])
>   File "/usr/local/lib/python3.10/dist-packages/impacket/structure.py", line 495, in calcUnpackSize
>     return self.calcUnpackSize(two[0], data)
>   File "/usr/local/lib/python3.10/dist-packages/impacket/structure.py", line 527, in calcUnpackSize
>     return data.index(b('\x00'))+1
> ValueError: subsection not found

When this occurred, the SMBConnection object was created simply with: SMBConnection(ip_addr, ip_addr, timeout=20) immediately prior to the login method being called.

Additional context

I suspect the remote Windows host is just dropping the connection, timing out, or otherwise terminating the conversation early and Impacket isn't handling it cleanly. I would expect Impacket to catch this during parsing and return a cleaner error report/exception that helps the user understand more about what failed.