Re: [Full-disclosure] VNC viewers: Clipboard of host automatically sent to remote machine

INSECURE i mean*

On 25 January 2012 21:30, Christian Sciberras <uuf6429@xxxxxxxxx> wrote:
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
passed when pasting. An example of this is when one copy+pastes a file.
See the Windows Clipboard API for more info.


On Wed, Jan 25, 2012 at 10:54 AM, Mario Vilas <mvilas@xxxxxxxxx> 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

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@xxxxxx> 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

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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