Re: virtual consoles

[Tavis Ormandy <taviso () gmail com>]

On Mon, Dec 02, 2019 at 06:28:12PM +0100, Solar Designer wrote:
> On Mon, Dec 02, 2019 at 08:56:38AM -0800, Tavis Ormandy wrote:
> > Regardless of your position, this is certainly possible on desktop Linux
> > too, unprivileged users can start a new X server and switch virtual
> > console, even over ssh.
> >
> > e.g.
> >
> > $ dbus-send --system --print-reply --dest=org.freedesktop.login1 /org/freedesktop/login1/seat/seat0 
> > org.freedesktop.login1.Seat.SwitchTo uint32:2
> >
> > (note: object paths may vary by distro, change the 2 to a different
> > number if you're already on VT2, or seat0 if you're on a different seat)
>
> If this in fact works over SSH and from a user account different than
> the one logged in on the currently active virtual console, then I'd say
> it's a vulnerability on its own, regardless of the social engineering
> aspects you mention.

Definitely does on Fedora and Ubuntu, an entirely remote unprivileged
user can use it, even if root is logged in at the virtual console.

It's very simple to switch to an X server displaying a fake screensaver
while the user is sitting there.

> Why does this functionality even exist?
>
> > Should this have some policykit action requirement, or require physical
> > presence? I don't know the answer.
>
> Maybe simply drop the misfeature?
>
> Alexander

That would make things simpler! I can't think of any reason this would
ever be useful.

Tavis

-- 
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taviso () sdf lonestar org | finger me for my pgp key.
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