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TESO Security Advisory
09/03/2000

atsadc local root compromise


Summary
===================

    The atsar application contains an exploitable vulnerability.

    The Halloween 4 Linux distribution, which is based on RedHat 6.1 is
    shipped with this suid-root program. It might be used to gain superuser
    privileges.


Systems Affected
===================

    Halloween 4 Linux distribution, maybe others too.
    Any system that has atsar-linux-1.4.2 package installed.


Tests
===================

    liane:[bletchley]> id -a
    uid=501(bletchley) gid=501(bletchley) groups=501(bletchley)
    liane:[bletchley]> uname -a
    Linux liane.c-skills.de 2.2.13-13 #21 Thu Mar 2 10:36:13 WET 2000 i686 unknown
    liane:[bletchley]> stat `which atsadc`
      File: "/usr/sbin/atsadc"
      Size: 16000        Filetype: Regular File
      Mode: (4755/-rwsr-xr-x)         Uid: (    0/    root)  Gid: (    0/    root)
    Device:  3,1   Inode: 117038    Links: 1
    Access: Thu Mar  9 10:09:37 2000(00000.01:02:49)
    Modify: Tue Nov  9 23:57:50 1999(00120.11:14:36)
    Change: Tue Mar  7 14:55:23 2000(00001.20:17:03)
    liane:[bletchley]> cd atsar-hack/
    liane:[atsar-hack]> ./ass.pl
    Creating hijack-lib ...
    Compiling hijack-lib ...
    Compile shell ...
    Invoking vulnerable program (atsadc)...
    sh: error in loading shared libraries:
    sh: error in loading shared libraries:
    Welcome. But as always: BEHAVE!
    sh-2.03# id -a
    uid=0(root) gid=0(root) groups=501(bletchley)
    sh-2.03#


    We've created a full working root-exploit which can be obtained from
    [1] or [2].
    To work properly the /etc/ld.so.preload file must not exist.
    If it already exist, attackers may use other config-files to gain
    root access.


Impact
===================

    The vulnerable program 'atsadc' is shipped on the power-tools/contrib
    CD and comes per default suid root (package "atsar-linux").
    Attackers might use this program with obscure command-line-options to
    gain locally root-access.


Explanation
===================

    Atsadc doesn't properly check permissions of the output-file given
    on the command-line. Rather it opens the file without the O_EXCL flag,
    allowing an attacker to overwrite any file he wishes.
    Due to the nice mode of 0664 an attacker may even create new files where
    he has write-access too (group -rw).
    In interaction with other linux 'system-tools' he can gain root-access.


Solution
===================

    Remove the suid-bit.
    The vendor and the author has been informed before, so a patch is already
    available.


Acknowledgments
================

    The bug-discovery, further analyzation and the exploit was done by

    S. Krahmer -- http://www.cs.uni-potsdam.de/homepages/students/linuxer/

    This advisory has been written S. Krahmer


Contact Information
===================

    The TESO crew can be reached by mailing to tesopub@coredump.cx.
    Our web-page is at http://teso.scene.at/

    "C-Skills" developers may be reached through [1].


References
===================

    [1] S. Krahmer, C-Skills
        http://www.cs.uni-potsdam.de/homepages/students/linuxer/

    [2] TESO
  http://teso.scene.at


Disclaimer
===================

    This advisory does not claim to be complete or to be usable for any
    purpose. Especially information on the vulnerable systems may be
    inaccurate or wrong. The supplied exploit is not to be used for malicious
    purposes, but for educational purposes only.

    This advisory is free for open distribution in unmodified form.
    Articles that are based on information from this advisory should include
    link [1] and [2].


Exploit
===================

    We've created a working exploit to demonstrate the vulnerability.

    The exploit is available on either

       http://teso.scene.at/
    or
       http://www.cs.uni-potsdam.de/homepages/students/linuxer/


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