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ESB-2006.0412 -- [AIX] -- Denial of service vulnerability in sendmail

Date: 15 June 2006
References: AL-2006.0048  

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             AUSCERT External Security Bulletin Redistribution

                          ESB-2006.0412 -- [AIX]
                Denial of service vulnerability in sendmail
                               15 June 2006


        AusCERT Security Bulletin Summary

Product:              Sendmail
Publisher:            IBM
Operating System:     AIX 5.2 and 5.3
Impact:               Denial of Service
Access:               Remote/Unauthenticated
CVE Names:            CVE-2006-1173

Ref:                  AL-2006.0048

- --------------------------BEGIN INCLUDED TEXT--------------------

Hash: SHA1


First Issued: Wed Jun 14 11:00:00 CDT 2006
                           VULNERABILITY SUMMARY

VULNERABILITY:      A MIME handling issue in sendmail may allow a remote
                    user to cause a denial of service.

PLATFORMS:          AIX 5.2 and 5.3.

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

THREAT:             A remote user may cause a denial of service.

CERT VU Number:     CVE-2006-1173
CVE Number:         VU#146718
                           DETAILED INFORMATION

I.  Description

Sendmail is a Mail Transfer Agent that ships with the AIX operating system.
It is used for routing mail for local and network delivery. A vulnerability
was discovered in sendmail that may allow a remote attacker to cause a
denial of service. This vulnerability may be exploited via a specially
crafted MIME encoded message. IBM is providing patches that remove possible
attack vectors for this vulnerability. These patches should be installed as
a precautionary measure.

A specially crafted MIME encoded message may cause sendmail processes
involved in queuing messages to reach the process stack size limit
resulting in a core dump. If the system is configured to use uniquely named
core files an attacker may be able to fill the filesystem. Furthermore, if
a process involved in mail queuing exits other messages in the queue may
be lost.

sendmail ships as part of the fileset.

II. Impact

A remote attack may fill a filesystem or cause messages in the mail queue
to be lost. Note that this issue may not be exploited to cause sendmail to
stop accepting connections.

III.  Solutions

A. Official Fix

IBM provides the following fixes:

      APAR number for AIX 5.2.0:  IY85930 (available approx. 08/23/06)
      APAR number for AIX 5.3.0:  IY85415 (available approx. 08/09/06)

NOTE: Affected customers are urged to upgrade to the latest applicable
Technology Level.

B. Interim Fix

Interim fixes are available. The ifixes can be downloaded via ftp from:

sendmail_vu146718.tar.Z is a compressed tarball containing this advisory,
interim fix packages and cleartext PGP signatures for each package.

Verify you have retrieved the fixes intact:
The interim fixes below are named by using the APAR corresponding to the
release that the fix applies to. The APAR is followed by an underscore and
the Technology Level for the particular AIX release that a fix applies to.

The checksums below were generated using the "sum" and "md5sum" commands
and are as follows:

The interim fixes below include prerequisite checking. This will enforce
the correct mapping between the fixes and AIX Technology Levels. When
installing these fixes, it will be necessary to remove other interim fixes
which modify sendmail. Note that these interim fixes also address CERT

Filename                  sum           md5
IY85930_06.060610.epkg.Z  26388   568   f6b6cf4021dfe9a17022552b57d19015
IY85930_07.060610.epkg.Z  49019   569   70c6004b90862ca92c97f1d0f31d716a
IY85930_08.060610.epkg.Z  23261   568   3ceb1567373824fdbbb2c6b53cab3292
IY85415_02.060609.epkg.Z  46935   587   d2190ed78a2137adc0f00f17c8cd4f3b
IY85415_03.060609.epkg.Z  51225   587   76b73ad4d68be044abb6b1d2870eb87f
IY85415_04.060609.epkg.Z  17202   587   bad156de21607a09e9332c7ae4cd20d1

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
and describe the discrepancy.

The following table shows the prerequisite lower and upper fileset levels
for the fixes above. These levels are inclusive and apply to

Filename                    Lower Level     Upper Level

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

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

Interim Installation Instructions:

IMPORTANT: If interim fixes for CERT VU#834865 are installed, they will
have to be uninstalled before these interim fixes can be applied. Note that
these interim fixes also address CERT VU#834865. 

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

Stop sendmail. This can be done by executing the following command:

# stopsrc -s sendmail

To preview an epkg ifix installation execute the following command:

# emgr -e ipkg_name -p       # where ipkg_name is the name of the
                             # ifix package being previewed.

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

# emgr -e ipkg_name -X       # where ipkg_name is the name of the
                             # ifix package being installed.

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

Start sendmail. This can be done by executing the following command:

# startsrc -s sendmail -a "-bd -q30m"

Verify that sendmail was started:

# lssrc -s sendmail
Subsystem         Group            PID          Status
 sendmail         mail             16000        active

C. Workaround

Turn sendmail off
If sendmail is not needed, turn it off. This can be done by using the
stopsrc command:

# stopsrc -s sendmail

Verify that sendmail is no longer running:

# lssrc -s sendmail
Subsystem         Group            PID          Status 
 sendmail         mail                          inoperative

To prevent sendmail from starting on boot, edit the /etc/rc.tcpip startup

Set MaxMessageSize in /etc/ such that sendmail will reject a
messages large enough to cause sendmail to reach the process stack size
limit. Instead of dumping core sendmail will reject the message.

IV. Obtaining Fixes

AIX Version 5 APARs can be downloaded from:

Security related Interim Fixes can be downloaded from:

V.  Contact Information

If you would like to receive AIX Security Advisories via email, please

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

To request the PGP public key that can be used to communicate securely
with the AIX Security Team send email to
with a subject of "get key". The key can also be downloaded from a PGP
Public Key Server. The key id is 0x1B14F299.

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
Version: GnuPG v1.4.3 (GNU/Linux)


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