107326 2003-07-08 21:54 /49 rader/ Hugo Vázquez Caramés <overclocking_a_la_abuela@hotmail.com> Importerad: 2003-07-08 21:54 av Brevbäraren Extern mottagare: bugtraq@securityfocus.com Mottagare: Bugtraq (import) <5450> Ärende: 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@infohacking.com (107326) /Hugo Vázquez Caramés <overclocking_a_la_abuela@hotmail.com>/(Ombruten)