bugtraq - Qt temporary files race condition in Knoppix 3.1

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Date: 8 Jul 2003 15:48:51 -0000
From: Hugo "Vázquez" "Caramés" <overclocking_a_la_abuela@...mail.com>
To: bugtraq@...urityfocus.com
Subject: Qt temporary files race condition in Knoppix 3.1

Qt libaries works with KDE. Knoppix 3.1 comes with KDE3. A default 
installation on hard disk of this live CD linux distribution with the SSHD 
daemon running may allow a serious D.o.S. attack and potential root 
compromise.

I've found a race condition in knoppix 3.1 live CD. I've confirmed it on 2 
different installations on hard disk done with the "knx-hdinstall" tool.
Procedure:
1) After booting knoppix from the CD I set the root passwd
2) I use knx-hdinstall

Knoppix by default goes to init 5 at startup, so "kdm" is started.
If you start a session with any user you can see:
On /tmp you can see a directory ".qt" with this permissions:
drwxr-xr-x root root 
Inside /tmp/.qt/ the are two files: "qt_plugins_3.0rc" 
and "qt_plugins_3.0rc.lock", both owned by root.

The /tmp directory is world writable so it's trivial to exploit this flaw 
with a symlink attack.

I have exploited it with a ".bash_profile" inside /home/knoppix/ with 
something like this:

--------------- .bash_profile --------------------
mkdir /tmp/.qt
ln -s <file_owned_by_root> /tmp/.qt/qt_plugins3.0rc
---------------------------------------------------

All you have to do is waiting for a reboot, then an automated script (I've 
been able to do it by hand) will try to log in via SSH with "knoppix" user 
before "kdm" is started (it's really easy) and your bash profile will be 
loaded. The symlink you created will force the overwriting of 
<file_owned_by_root>. D.o.S. is trivial: the attacker can overwrite any 
file in the system.

Exploitation to get root privileges is harder but not imposible. Soon we 
will have some proof of concept exploit to show potential dangerous 
scenarios at:

http://www.infohacking.com

Regards,

Hugo Vázquez Caramés
hugo@...ohacking.com