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Re: VNC viewers: Clipboard of host automatically sent to remote machine
From: Giles Coochey <giles () coochey net>
Date: Tue, 24 Jan 2012 15:32:33 +0000

On 2012-01-24 13:34, Ben Bucksch wrote:
Affected Products: GNOME Vinagre and many other VNC viewers

1. On your trusted desktop (e.g. Linux), open a text editor
2. Type "My password", select the text, and hit Ctrl-C
3. Open a Vinagre VNC connection to a remote host, e.g. running an
untrusted Windows
4. On the remote Windows host, open notepad.exe
5. In notepad's menu bar, using the mouse, click on Edit|Paste

Actual result:
notepad.exe shows "My password"
Expected result:

Because I use a different password for every service, I have to
copy&paste them
(on my trusted desktop).

However, the remote machine is not trusted. In some cases, it's owned 
a different company, in other cases I use VNC and a different machine
specifically because I don't trust the software and want it jailed. 
the untrusted host can get to my passwords from my trusted desktop,
that's a critical security hole, because my passwords leak, and they 
well give full access to other machines, my bank account or other 
sensitive data.

Affected users:
Using VNC is common usage pattern also used by government agencies
handling highly sensible documents (on the trusted host desktop 
while moving dangerous but necessary uses like Internet access, 
and similar needs on physically different machines that are accessed 
The purpose is that the untrusted system has no way to get to the
on the trusted desktop, but that assumption is violated here.

Even normal users will be at risk. Many copy&paste passwords, or they
copy&paste snipplets of sensitive Word processing documents, e.g.
business plans.

Given that most users are unaware of this risk, although the danger 
nevertheless be very real for them, it is necessary for the default
configuration to be secure. They cannot be expected to actively 
preferences or the software to protect themselves, because the 
isn't obvious in the first place.

   Possible solutions:
1) a pref, with default off and a clear warning about this problem,
because many users will not be aware of it. A pref with default on or
without a clear warning is *not* sufficient.
2) Better yet: A button on the toolbar "Copy clipboard" Text is 
from host desktop clipboard to remote machine clipboard only when 
button is pressed.
3) A combination of 1) and 2)

Many viewers, including RealVNC have the option to disable the shared 
clipboard. Check your preferences.

Message sent via my webmail account.

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