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

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Date: Thu, 31 Jul 2003 16:17:27 -0400
From: MightyE <trash@...htye.org>
To: David Riley <oscar@...-rileys.net>, bugtraq@...urityfocus.com
Subject: Re: Another Mac OS X ScreenSaver Security Issue (after Security 
 	  Update 2003-07-14)



>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.
>  
>
Yes, this would certainly be pretty sad, but as I see it, the 
screensaver is one of the most important local (non remote) security 
devices, it protects against casual cracking attempts of using a 
restricted application that was left running when someone was called 
away from their desk.  Although a root expoit on the screensaver would 
be worse than merely crashing the screensaver, neither are tolerable if 
you ask me, so may as well stress test the screensaver engine till you 
can rely on it, then trust it with root access.

>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.
>
A developer could add a --PERMIT_KILL option while testing their 
screensaver which would tell Escape Pod that it's ok to kill this 
process when the request came in.  Also if they had a remote terminal 
up, and root access, they could always kill it that way.  As I see it, a 
user really needs to be able to depend on their screensaver to protect 
their workstation while they're not at it.  A person doesn't necessarily 
have the option of logging out of their workstation completely when they 
go away from their desk, nor the time to take other security steps.

It's true that someone having physical access to your machine (and a 
desire to use such access for evil) gives them a level of control that 
can't be truly protected against with a screensaver of any calibre, but 
it does protect the payroll manager from having one of his lackeys give 
himself a pay raise while he's at a meeting.

-e