Qt temporary files race condition in Knoppix 3.1

From: Hugo (overclocking_a_la_abuela_at_hotmail.com)
Date: 07/08/03

  • Next message: Mandrake Linux Security Team: "MDKSA-2003:073 - Updated unzip packages fix vulnerability"
    Date: 8 Jul 2003 15:48:51 -0000
    To: bugtraq@securityfocus.com
    
    
    ('binary' encoding is not supported, stored as-is)

    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


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