bugtraq - Re: Another Mac OS X ScreenSaver Security Issue (after Security Update 2003-07-14)

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Message-ID: <Pine.NEB.4.53.0307311547250.1560@duality.the-rileys.net>
Date: Thu, 31 Jul 2003 15:53:44 -0400 (EDT)
From: David Riley <oscar@...-rileys.net>
To: MightyE <trash@...htye.org>
Subject: Re: Another Mac OS X ScreenSaver Security Issue (after Security  	
  Update 2003-07-14)

On Thu, 31 Jul 2003, MightyE wrote:

> If anything I'd call this a security consideration of Escape Pod.
> Perhaps Escape Pod should try to talk to the process it's about to kill,
> and get its 'permission' for killing, and failing a timely response (2
> secs?), drop the program.  ScreenSaverEngine would have to be tailored
> to respond to such a request.

That would be nice, though I can't really imagine Apple changing a rather
core part of their system architecture for a shareware developer's free
utility (though atmittedly, it is a rather large and important Mac
developer).  It would be an interesting standard to set for a number of
platforms, similar to a "watchdog timer" on a number of microcontrollers
and other devices that resets the device if the timer isn't reset withn x
number of cycles, which would indicate a crash.

> On Linux, doesn't xscreensaver run as root?  Wouldn't this be another
> option here (I'm admittedly unfamiliar with Mac OS X), preventing Escape
> Pod from even being capable of terminating the screensaver process?  Or
> does Escape Pod also run as root?

This is a good idea, except for two (and possibly more) problems:

a) If the screensaver engine is compromised (as it was earlier this month,
though likely not in a command-execution sort of way), you don't want to
be able to give the user root privileges.  Presumably, xscreensaver has
safeguards against that (or they assume it'll never be exploited).  It
would be pretty sad to have a root security hole through the screensaver.

b) Sometimes the screensaver does crash.  Keep in mind that since the
screensaver modules are executable code (as xscreensaver modules probably
are as well, though I've never made one), that's the responsibility of the
individual screensaver developer to fix.  It's nice to be able to kill it
when it does crash so that you can use the computer again.