full-disclosure - Strange interactions between tunnelling and SMB under the proprietary Microsoft Windows environment

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Message-ID: <20060330055210.GA8941@alphanet.ch>
Date: Thu Mar 30 06:54:33 2006
From: schaefer at alphanet.ch (Marc SCHAEFER)
Subject: Strange interactions between tunnelling and SMB
	under the proprietary Microsoft Windows environment

Hi,

first, a disclaimer: I don't really need the proprietary Microsoft
Windows environment for my work. It happens that, for interoperability's
sake, I sometimes install free (libre) software on this proprietary
environment on customer systems. It's always quite painful, has strange
implications, and is always quite difficult to debug. But well, some
people apparently still need it.

After that, the issue I saw, which I currently cannot understand:

   I installed the libre software OpenVPN including the TAP driver on
   the proprietary Microsoft Windows environment. I did set up a
   encrypted tunnel between two machines on the same Ethernet subnet
   (this is probably important).

   Testing pings and telnet on the remote tunnel address (e.g.
   192.168.1.2) and capturing data with the libre software Ethereal on the
   real Ethernet interface did show me that the flow of data was
   correctly routed through the tunnel.

   However, accessing \\192.168.1.2\c$ did go through the Ethernet
   interface, and *not the tunnel*, and strangely half-using the private
   addresses!

   I wonder if there is some NetBEUI/NetBIOS/whatever interaction which
   kind-of `resolves' the private IP address as a host name. Thus
   probably as long as noone replies NetBEUI/NetBIOS it should work ...
   but could be exploitable, isn't it ?

   The obvious solution could be to completely disable this resolution,
   or maybe use a real DNS name for the private addresses of the tunnel.

   After all NetBEUI/NetBIOS predates the standard IP networking support
   in the proprietary Microsoft Windows environment and could be considered
   obsolete today (if using a WINS server or DNS resolution). But it is
   still activated by default.

   Looking at the routing tables through NETSTAT.EXE is ... well ...
   strange. No interface, strange routes, it's a bit difficult to really
   understand how routing works on this proprietary plateform.

Has someone also experienced this, or was it some strange local pecularity ?