IBM AIX: Buffer Overflow Vulnerability in libi18n Library

["IBM MSS Advisory Service" <advisory () us ibm com>]

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18 JUL 2001  23:47 GMT                              MSS-OAR-E01-2001:271.1
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IBM SECURITY ADVISORY

Thu Jun 28 10:06:00 CDT 2001
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                           VULNERABILITY SUMMARY

VULNERABILITY:    Buffer Overflow Vulnerability in libi18n Library

PLATFORMS:        IBM AIX 4.3.x and 5.1

SOLUTION:         Apply the emergency-fixes described below, or
                  employ the workaround, also described below.

THREAT:           Malicious local user could obtain root privileges.

CERT Advisory:    NONE.

CVE candidate:    CAN-2001-0533

===========================================================================
                           DETAILED INFORMATION

I.  Description

    AIX ships with the library "libi18n" located in the "/usr/ccs/lib"
    directory. This library contains a function that is vulnerable
    to a buffer overflow through the LANG environment variable.

    An ordinary user has the ability to set the "LANG" environment
    variable to any value they choose. When this variable is set to a
    suitably formatted string and a program is run which uses the
vulnerable
    library, the program will terminate abnormally. If this program is also
    setuid root, aixterm for example, a malicious user has an opportunity
    to spawn a root shell and gain control of the machine.

II. Impact

   A malicious local user can use a well-crafted exploit code
   to gain root privileges on the attacked system, compromising the
   integrity of the system and its attached local network.

III.  Solutions

  A.  WORKAROUND

      If you do not wish to install the efix for this vulnerability
      but instead wait for the APAR that fixes it to be made
      available, you can also negate this vulnerability by making the
      "aixterm" program to be non-SUID. You must be "root" to do this.
      Ordinary users will still be able to use the program, although there
      may be unexpected side effects.

  B.  Official Fix

      IBM is working on the following fixes which will be available
      soon:

           AIX 4.3.x   -  IY20867
           AIX 5.1.0   -  IY21309

      NOTE: Fix will not be provided for versions prior to 4.3 as
      these are no longer supported by IBM. Affected customers are
      urged to upgrade to 4.3.3 at the latest maintenance level,
      or to 5.1.

  C.  How to minimize the vulnerability

    Temporary fixes for AIX 4.3.x and 5.1 systems are available.

    The temporary fixes can be downloaded via ftp from:

    ftp://aix.software.ibm.com/aix/efixes/security/libi18n_efix.tar.Z

    The efix tarball consists of a patched libi18n tarred binary which is
    compatible with both 4.3.x and 5.1.0 releases.  A copy of this Advisory
    is included in the efix tarball.

    These temporary fixes have not been fully regression tested; thus,
    IBM does not warrant the fully correct functioning of the efix.
    Customers install the efix and operate the modified version of AIX
    at their own risk.

    To proceed with efix installation:

    First, verify the MD5 cryptographic hash sums of each efix files
    you obtain from unpacking the efix tarball with those given below.
These
    should match exactly; if they do not, double check the hash results
    and the download site address. If OK, contact IBM AIX Security at
    security-alert () austin ibm com and describe the discrepancy.

    Filename        sum             md5
    =================================================================
    libi18n.tar    34706   130      1227c815533ae2f70a0eac71c5016263

    Efix Installation Instructions:
    -------------------------------

    IMPORTANT NOTICE: Before installing the efix, you must upgrade
    to the latest maintenance level of AIX for your version of AIX.

    1. Become root, if not already done.

    2. Change to the /usr/ccs/lib directory. Make a backup copy of the
       existing libi18n.a binary, giving it a distinctive, meaningful
       name, such as "libi18n.a.original" or "libi18n.a.backup". This
       is IMPORTANT to do, so you can recover the original libi18n.a
       binary if something goes wrong during the installation of the efix!

    3. In the root ("/") directory, download, uncompress, and untar
       the efix.

       a. uncompress libi18n_efix.tar.Z
       b. tar -xvf libi18n_efix.tar

    4. You will have a tarfiles named "libi18n.tar".
       You may discard the other, unneeded tarfile.

       Untar the tarfile by executing "tar -xvf libi18n.tar".
       The efix version of libi18n will be untarred and placed
       in the proper directory.

    5. Check to be certain that the new libi18n.a library
       is assigned proper permissions, "-r--r--r--", and the ownership
       is assigned properly, "bin" and "bin".


IV. Obtaining Fixes

IBM AIX APARs may be ordered using Electronic Fix Distribution (via the
FixDist program), or from the IBM Support Center.  For more information
on FixDist, and to obtain fixes via the Internet, please reference

        http://techsupport.services.ibm.com/rs6k/fixes.html

or send email to "aixserv () austin ibm com" with the word "FixDist" in the
"Subject:" line.

To facilitate ease of ordering all security related APARs for each AIX
release, security fixes are periodically bundled into a cumulative APAR.
For more information on these cumulative APARs including last update and
list of individual fixes, send email to "aixserv () austin ibm com" with
the word "subscribe Security_APARs" in the "Subject:" line.


V.  Acknowledgments

    Many thanks go to Troy Bollinger of IBM MSSD for discovering this
    vulnerability and for demonstrating its exploitation.

VI.  Contact Information

Comments regarding the content of this announcement can be directed to:

   security-alert () austin ibm com

To request the PGP public key that can be used to encrypt new AIX
security vulnerabilities, send email to security-alert () austin ibm com
with a subject of "get key".

If you would like to subscribe to the AIX security newsletter, send a
note to aixserv () austin ibm com with a subject of "subscribe Security".
To cancel your subscription, use a subject of "unsubscribe Security".
To see a list of other available subscriptions, use a subject of
"help".

IBM and AIX are a registered trademark of International Business
Machines Corporation.  All other trademarks are property of their
respective holders.
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