Questions about the SECURITY extension, and X security generally

[Mark Seaborn]

Chris Palmer <chris at noncombatant.org> wrote:

> I want to enjoy the benefits of the X SECURITY extension, such as with
> OpenSSH's -X (vs. -Y) option.

I wouldn't bother using the old X Security extension.  It only
provides two protection domains, called "trusted" and "untrusted".
Imagine a multi-user operating system that only allowed two users, or
that could only run two processes.

> I want to be able to stop X clients running on remote servers from being
> able to e.g. take a screenshot of other (local client) windows or log
> keystrokes intended for other (local) clients.

You have three options:
 * Use Xpra (http://partiwm.org/wiki/xpra).  It will forward X connections
   and though it was not intended to be a security tool I belive it does
   have the property you want.
 * Use SELinux, which makes use of the X server's XACE hooks.
 * Write your own extension that uses the X server's XACE hooks.

> Using a dumb keylogger I wrote (my first raw X program) and scrot, I can
> read all keystrokes and take a screenshot of the whole screen, from a remote
> machine that I connected to with "ssh -X".

On what system?  On Debian/Ubuntu, -X and -Y do the same thing.  (See
ForwardX11Trusted in the ssh_config man page and
http://plash.beasts.org/wiki/X11Security.)

Mark