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ESB-2005.0095 -- IBM Security Advisory -- Remotely exploitable vulnerability when configured to use NIS

Date: 01 February 2005

Click here for printable version
Click here for PGP verifiable version
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             AUSCERT External Security Bulletin Redistribution

                  ESB-2005.0095 -- IBM Security Advisory
       Remotely exploitable vulnerability when configured to use NIS
                              1 February 2005

===========================================================================

        AusCERT Security Bulletin Summary
        ---------------------------------

Product:           NIS
Operating System:  AIX 5.3
Impact:            Root Compromise
Access:            Remote/Unauthenticated

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IBM SECURITY ADVISORY

First Issued: Sun Jan 30 15:30:27 CST 2005

===========================================================================
                           VULNERABILITY SUMMARY

VULNERABILITY:      A remote user may gain root access to a system
                    configured as a NIS client. 

PLATFORMS:          AIX 5.3.

SOLUTION:           Apply the workaround, efix or APAR as described
                    below.

THREAT:             A remote user may gain root access to a system
                    configured as a NIS client.

CERT VU Number:     N/A
CVE Number:         N/A
===========================================================================
                           DETAILED INFORMATION


I.  Description
===============

A vulnerability was discovered that can be exploited by a remote user to
gain root privileges. Note that it is also possible for a local attacker to
exploit this vulnerability. This vulnerability only affects AIX 5.3 when
configured as a NIS client. Versions of AIX prior to AIX 5.3 are not
affected by this issue.


II. Impact
==========
A remote attacker may gain root access to a system configured as a NIS
client.


III.  Solutions
===============

A. Official Fix

IBM provides the following fixes:

      APAR number for AIX 5.3.0:  IY67248 (available approx. 05/19/04)

NOTE: Affected customers are urged to upgrade to 5.3.0 at the latest
maintenance level.

B. Emergency Fix

Efixes are available for AIX 5.3.0. The efixes can be downloaded via ftp
from:

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

nis_efix.tar.Z is a compressed tarball containing this advisory, two efix
packages for 5.3.0 and a cleartext PGP signature for each efix package.
The efix package named IY67248_01.050128.epkg.Z is for AIX 5.3.0 with no
maintenance level applied. This efix has the filesets bos.rte.libc.5.3.0.5
and bos.rte.security.5.3.0.5 as prerequisites and will not install unless
these prerequisites are installed on the system. The efix package named
IY67248_00.050128.epkg.Z is for AIX 5.3.0 with maintenance level one
applied. This efix has the filesets bos.rte.libc.5.3.0.11 and
bos.rte.security.5.3.0.10 as prerequisites and will not install unless
these prerequisites are installed on the system.

Verify you have retrieved the efixes intact:
- - ---------------------------------------------
The checksums below were generated using the "sum" and "md5sum" commands
and are as follows:

Filename                 sum         md5
=====================================================================
IY67248_00.050128.epkg.Z 41289  4491 333bcc260883bbf50409f4874b6cb3a2
IY67248_01.050128.epkg.Z 60904  4420 38011246f7ddd4aefffa33b91633b13b  

These sums should match exactly. The PGP signatures in the compressed
tarball and on this advisory can also be used to verify the integrity
of the various files they correspond to. If the sums or signatures cannot
be confirmed, double check the command results and the download site
address. If those are OK, contact IBM AIX Security at
security-alert@austin.ibm.com and describe the discrepancy.

IMPORTANT: If possible, it is recommended that a mksysb backup of the
system is created. Verify it is both bootable, and readable before
proceeding.

These efixes 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.

Efix Installation Instructions:
- - --------------------------------
The efix package for AIX 5.3.0 with no maintenance level is named
IY67248_01.050128.epkg.Z and the efix package for AIX 5.3.0 with
maintenance level one installed is named IY67248_00.050128.epkg.Z.

These packages use the new Emergency Fix Management Solution to install
and manage efixes. More information can be found at:

     http://techsupport.services.ibm.com/server/aix.efixmgmt

To preview an epkg efix installation execute the following command:

# emgr -e epkg_name -p       # where epkg_name is the name of the
                             # efix package being previewed.

To install an epkg efix package, execute the following command:

# emgr -e epkg_name -X       # where epkg_name is the name of the
                             # efix package being installed.

It is strongly recommended that this efix be mount installed before doing
a regular install. A mount install will mount the patched binaries over
existing system binaries. If any issues arise, the efix can be unmounted or
the system can be rebooted to revert of the original system files. The
mount an epkg efix package, execute the following command:

# emgr -m epkg_name -X       # where epkg_name is the name of the
                             # efix package being installed.

The "X" flag will expand any filesystems if required.

C. Workaround

The system file /etc/passwd contains the string "+::0:0:::" when the system
is configured as a NIS client. To remove this vulnerability, that line
should be changed to "+:". Note that this change can only be done by the
root user.


IV. Obtaining Fixes
===================

AIX Version 5 APARs can be downloaded from:

     http://www-1.ibm.com/servers/eserver/support/pseries/aixfixes.html

Security related Emergency Fixes can be downloaded from:

     ftp://aix.software.ibm.com/aix/efixes/security

V.  Contact Information
========================

If you would like to receive AIX Security Advisories via email, please visit:
     https://techsupport.services.ibm.com/server/pseries.subscriptionSvcs

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 communicate securely
with the AIX Security Team send email to security-alert@austin.ibm.com
with a subject of "get key". The key can also be downloaded from a
PGP Public Key Server. The key id is 0x9391C1F2.

Please contact your local IBM AIX support center for any assistance.

eServer is a trademark of International Business Machines Corporation.
IBM, AIX and pSeries are registered trademarks of International Business
Machines Corporation. All other trademarks are property of their
respective holders.
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        http://www.auscert.org.au/render.html?it=3192

===========================================================================
Australian Computer Emergency Response Team
The University of Queensland
Brisbane
Qld 4072

Internet Email: auscert@auscert.org.au
Facsimile:      (07) 3365 7031
Telephone:      (07) 3365 4417 (International: +61 7 3365 4417)
                AusCERT personnel answer during Queensland business hours
                which are GMT+10:00 (AEST).
                On call after hours for member emergencies only.
===========================================================================

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