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 (at) infohacking (dot) com [email concealed]

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