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

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Message-ID: <CAD6s_XuXHMYzExvk+rpHeSkfHy077UZGxKqjgBJ2Y6e_zOmK3A@mail.gmail.com>
Date: Wed, 25 Jan 2012 11:30:43 +0100
From: Christian Sciberras <uuf6429@...il.com>
To: Mario Vilas <mvilas@...il.com>
Cc: full-disclosure@...ts.grok.org.uk
Subject: Re: VNC viewers: Clipboard of host automatically
 sent to remote machine

That's not necessarily true. On windows you can add custom clipboard formats
that would contain a 'link' to the original source, causing the data to be
actually
passed when pasting. An example of this is when one copy+pastes a file.
See the Windows Clipboard API for more info.

Chris.



On Wed, Jan 25, 2012 at 10:54 AM, Mario Vilas <mvilas@...il.com> wrote:

> I'm not sure how the clipboard works in Linux desktops (I understand
> it's a little different), but at least in Windows environments data
> has to be copied to the clipboard when you hit Ctrl-C. It can't be
> copied when you hit Ctrl-V because then the applications wouldn't know
> if there is anything to paste (like you said, the button would be
> grayed).
>
> So to replicate this behavior it's necessary to send the data as it's
> copied, not as it's pasted. Most (not all, but most) desktop systems
> assume clipboard data can be freely shared with all applications and
> don't have any kind of isolation at all. VNC was designed with the
> same idea.
>
> The bottom line is, the problem here is using VNC for what Ben is
> using it. There are many more problems with that scenario and
> clipboard sharing may be the least of them.
>
> On Wed, Jan 25, 2012 at 8:44 AM, Peter Osterberg <j@....nu> wrote:
> > On 01/24/2012 07:18 PM, Mario Vilas wrote:
> >>> Guys, could you please read carefully everything before you reply?
> >> I read carefully. It still didn't make sense, though.
> >>
> >>> And you wouldn't be allowed to use copy&paste while you edit sensitive
> >>> documents either, I guess?
> >> I don't know how you could get to such a conclusion from what I wrote.
> >>
> >> You're reporting that if you copy and paste sensitive information and
> >> connect to a VNC session your clipboard data gets sent to the remote
> >> machine. That's pretty obvious and not a security hole that needs to
> >> be plugged.
> >
> > I don't think that is what Ben is saying. The clipboard get sent to the
> > the server even before it is pasted, this happens without the user
> > knowing of it.
> >
> > Notepad would have the paste button grayed otherwise, if the clipboard
> > is empty, right? So it is already on the server before paste is pressed.
> >
> > So what ever was in the clipboard buffer is transmitted to the server on
> > connection.
> >
> > This is at least the assumption I make from reading Ben's mails. Or...
> > Is there a cliboard flag saying there is something on the clipboard, but
> > it isn't transmitted until the user actually pastes? I haven't really
> > got any experience with how the clipboard feature is implemented. My
> > assumption is however that it has to be on server for notepad to be
> > aware that Paste shouldn't be grayed out...
> >
> > I think Ben's report make complete sense actually, it would be better to
> > have the clipboard feature as a default. Security before features... =)
> >
> > _______________________________________________
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>
> --
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