full-disclosure - Re: VNC viewers: Clipboard of host automatically sent to remote machine

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Date: Tue, 24 Jan 2012 15:32:33 +0000
From: Giles Coochey <giles@...chey.net>
To: <full-disclosure@...ts.grok.org.uk>
Subject: Re: VNC viewers: Clipboard of host automatically
 sent to remote machine

On 2012-01-24 13:34, Ben Bucksch wrote:
> Affected Products: GNOME Vinagre and many other VNC viewers
>
> Reproduction:
> 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:
> Nothing.
>
> Impact:
> 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 
> by
> 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. 
> If
> the untrusted host can get to my passwords from my trusted desktop,
> that's a critical security hole, because my passwords leak, and they 
> may
> well give full access to other machines, my bank account or other 
> highly
> sensitive data.
>
> Affected users:
> Using VNC is common usage pattern also used by government agencies
> handling highly sensible documents (on the trusted host desktop 
> system)
> while moving dangerous but necessary uses like Internet access, 
> Windows
> system
> and similar needs on physically different machines that are accessed 
> via
> VNC.
> The purpose is that the untrusted system has no way to get to the
> information
> 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.
>
> Solution:
> Given that most users are unaware of this risk, although the danger 
> may
> nevertheless be very real for them, it is necessary for the default
> configuration to be secure. They cannot be expected to actively 
> change
> preferences or the software to protect themselves, because the 
> problem
> 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 
> copied
> from host desktop clipboard to remote machine clipboard only when 
> that
> 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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