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Home » Hacking News » Sendmail buffer overflow vulnerability in AIX

Sendmail buffer overflow vulnerability in AIX

by Nikola Strahija on March 3rd, 2003 This vulnerability allows a remote attacker to gain root privileges. At this time, there is no known exploit in the wild for this vulnerability.


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

Sendmail is a MTA (mail transfer agent) that routes mail for local or
network delivery. When sendmail receives a message it translates the
format of message headers to match the requirements of the destination
system. The program determines the destination via the syntax and content
of the address field in a message header. A vulnerability that exploits
how message headers are parsed has been found. This vulnerability allows
a remote attacker to gain root privileges. At this time, there is no known
exploit in the wild for this vulnerability.

The sendmail daemon runs on all versions of AIX by default. To determine
if sendmail is running on your system execute the following:

#lssrc -s sendmail

If sendmail is running, the following will be displayed:

Subsystem Group PID Status
sendmail mail xxxx active

Where xxxx is the pid of the sendmail process on your system.

If sendmail is not installed, the system is not vulnerable.


II. Impact
==========

A remote attacker can gain root privileges.


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

A. Official Fix
IBM provides the following fixes:

APAR number for AIX 4.3.3: IY40500 (available approx. 03/12/2003)
APAR number for AIX 5.1.0: IY40501 (available approx. 04/28/2003)
APAR number for AIX 5.2.0: IY40502 (available approx. 04/28/2003)

NOTE: Fixes 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 or 5.1.0 at the latest maintenance level.

B. E-fix
Temporary fixes for AIX 4.3.3, 5.1.0, and 5.2.0 systems are available.

The temporary fixes can be downloaded via ftp from:

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

The efix compressed tarball contains three fixes: one each for
AIX 4.3.3, AIX 5.1.0 and AIX 5.2.0. It also includes this Advisory
and a README file with installation instructions.

Verify you have retrieved this efix intact:
- - ---------------------------------------------
There are 3 fix-files in this package for the 4.3.3, 5.1.0, 5.2.0
releases. The checksums below were generated using the "sum" and
"md5" commands and are as follows:

Filename sum md5
=================================================================
sendmail.433 61331 428 013f747e5a447e2dec777e2e840914a9
sendmail.510 34257 1059 5f282fd2a472c2d75c88c3c652312842
sendmail.520 45494 1007 88bcb028aab4625abe0257d3537a0813

These sums should match exactly; if they do not, double check the
command results and the download site address. If those are OK,
contact IBM AIX Security at [email protected] and describe
the discrepancy.

IMPORTANT: Create a mksysb backup of the system and verify it is
both bootable, and readable before proceeding.

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.

Efix Installation Instructions:
- - ---------------------------------
Detailed installation instructions can be found in the README file
supplied in the efix package. These instructions are summarized below.

You need to have the following filesets installed. This ensures that
the proper versions of co-requisite system files, such as libc.a, are
installed:

For AIX 4.3.3:
bos.net.tcp.client.4.3.3.87

For AIX 5.1.0:
bos.net.tcp.client.5.1.0.38

For AIX 5.2.0:
bos.net.tcp.client.5.2.0.1

You can determine which fileset is installed by executing
the following:

# lslpp -L bos.net.tcp.client


1. Create a temporary efix directory and move to that directory.
# mkdir /tmp/efix
# cd /tmp/efix

2. Move the efix to /tmp/efix, uncompress it and un-tar the resulting
tarfile. Move to the fix directory.
# cp PATH_TO_ADVISORY /tmp/efix # where PATH_TO_ADVISORY is the fully
# qualified path to the efix package.
# uncompress sendmail_efix.tar.Z
# tar xvf sendmail_efix.tar
# cd sendmail_efix

3. Rename the patched binary files appropriate for your system and set
ownership and permissions.
# mv sendmail.xxx sendmail # where xxx is 433, 510 or 520
# chown root.system sendmail
# chmod 6551 sendmail

4. Create a backup copy of original binary. Remove all
permissions from the backup copy.
# cd /usr/sbin
# cp sendmail sendmail.orig
# chmod 0 sendmail.orig

5. Stop sendmail.
# stopsrc -s sendmail

6. Replace the current system binary with the patched
binary. Use the -p option to preserve the file
permissions set in step 3.
# cp -p /tmp/efix/sendmail_efix/sendmail /usr/sbin/sendmail

7. Restart sendmail.
# startsrc -s sendmail -a "-bd -q15"

The -bd flag starts sendmail as a daemon running in the
background as a Simple Mail Transfer Protocol (SMTP) mail router.

The -q15 flag tells the sendmail daemon to process the queue every
15 minutes.

It may be desirable to initialize sendmail differently on the
system being patched. Modify the flags accordingly.

C. Workaround
Turn sendmail off. You can do this by executing the following:
# stopsrc -s sendmail

Note that legitimate requests to sendmail will fail. If this is not feasible
in your environment, please apply the efix as described in Section III B.


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 "[email protected]" with the word "FixDist" in the
"Subject:" line.

AIX APARs may also be downloaded from the web from the following URLs.

For 4.3.3 APARs:
http://techsupport.services.ibm.com/rs6k/fixdb.html

For 5.1.0 APARs:
http://techsupport.services.ibm.com/server/aix.fdc

For 5.2.0 APARs:
http://techsupport.services.ibm.com/server/aix.fdc

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 "[email protected]" with
the word "subscribe Security_APARs" in the "Subject:" line.


V. Acknowledgments
==================

The AIX Security Team would like to thank Sendmail, Inc. for bringing this
issue to our attention.

This document was written by Shiva Persaud.


VI. Contact Information
========================

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

[email protected]

To request the PGP public key that can be used to encrypt new AIX
security vulnerabilities, send email to [email protected]
with a subject of "get key".

If you would like to subscribe to the AIX security newsletter, send a
note to [email protected] 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".

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

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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