Vulnerability Development mailing list archives

Re: Possible flaw in XFree?


From: Nuno Branco <branco () markdata pt>
Date: 28 Jun 2002 17:16:41 +0100


try to start your Xserver with the command

[root@machine branco]$ startx && exit

Maybe it will do the trick :)


On Thu, 2002-06-27 at 20:06, William N. Zanatta wrote:
Hi folks,

   Talking about some bad experiences with my friend, I discovered (he 
told me) it is possible to abort a X session even when the screen is 
locked by some kind of application like 'xlock'.

   I have made the following test:

   1. Logged into the system as 'william' (a normal non-privileged user).
   2. startx
   3. Run xlock
   ... the screen is now locked...
   4. Tried a hit on some keys. The password screen appears.
   5. Then, 'ctrl-alt-backspace' and voila... X is down and my console 
is there, opened for me.

   I see this as a serious problem once one could let his/her X session 
opened and locked and anyone who have access to that machine could abort 
the X session and start playing around with the logged user's shell 
(which could be the root shell).

   What about that?

   Tested on:
-------------------------------------
XFree86 Version 4.1.0 / X Window System
(protocol Version 11, revision 0, vendor release 6510)
Release Date: 2 June 2001
         If the server is older than 6-12 months, or if your card is
         newer than the above date, look for a newer version before
         reporting problems.  (See http://www.XFree86.Org/FAQ)
Build Operating System: Linux 2.2.19 i686 [ELF]
-------------------------------------

   Regards,

   William Zanatta

-- 
Perl combines all of the worst aspects of BASIC, C and line noise.
                 -- Keith Packard

-- 
Atentamente, 
Nuno Branco

MARKDATA
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1150-248 Lisboa 
Telefone: 213173400 
Fax: 213155046 

http://www.markdata.net/


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