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[Samba] Accessing a guest share from Windows 10 gives System error 5 on some computers


I have an embedded instrument running samba 4.4.5 or 4.6.2 that connect to Windows / Mac / Linux via USB RNDIS / CDC Ethernet.
On those instrument, there's a single share that is configured for guest access without password:

   log level = 10
   workgroup = DATA
   server string = Samba Server
   log file = /var/log/samba/log.%m
   max log size = 50
   security = user
   map to guest = Bad User
   path = /var/db/instrument-data
   available = yes
   browsable = yes
   public = yes
   writable = no

Locally on the instrument, I can run `smbclient -N -L localhost` and see that share.

The behavior is consistent on a per-computer basis. I can either access the share on any instrument without problems on one computer, or on another computer I cannot and the symptom is a `net view <instrument-name>` returning "System error 5, Access denied".
The computers currently run a mix of Windows 10's Anniversary Update (14393) or Creators Update (15063) and there doesn't seem to be a correlation regarding that.

I tcpdumped both types of sessions, and these show that the Windows Client forcefully closes the TCP connection (NT_STATUS_CONNECTION_RESET) right  after receiving `NTLMSSP_CHALLENGE` before a working client would send `NTLMSSP_AUTH` with a user.

I have checked setting `AllowInsecureGuestAuth` in the geristry without any effect.


Best regards
Kai Ruhnau
Software Manager
T:+49 202 769302 19

Target Systemelektronik GmbH & Co. KG
Heinz-Fangman-Straße 4
42287 Wuppertal

Amtsgericht Wuppertal HRA 23898
Persönlich haftende Gesellschafterin
Target Systemelektronik Beteiligungs GmbH
Heinz-Fangman-Straße 4, 42287 Wuppertal
Amtsgericht Wuppertal HRB 25346
Geschäftsführer: Jürgen Stein
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