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UNIRAS Brief - 277/06 - IBM SECURITY ADVISORY: Race condition vulnerability in sendmail [Updated 04/07/06 0849 CDT]



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   UNIRAS (UK Govt CERT) Briefing Notice - 277/06 dated 10.04.06  Time: 14:25  
  UNIRAS is part of NISCC (National Infrastructure Security Co-ordination Centre)
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  UNIRAS material is also available from its website at www.uniras.gov.uk and
         Information about NISCC is available from www.niscc.gov.uk
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Title
=====

IBM SECURITY ADVISORY: Race condition vulnerability in sendmail [Updated 04/07/06 0849 CDT]

Detail
====== 

A vulnerability was discovered in sendmail that may allow a remote attacker
to execute arbitrary code. This vulnerability is caused by a race condition
that occurs when handling asynchronous signals. Sendmail is a Mail Transfer
Agent that ships with the AIX operating system. It is used for routing mail
for local and network delivery. IBM is providing patches that remove
possible attack vectors for this vulnerability. These patches should be
installed as a precautionary measure.




 
AIX 5.3 : Security advisories (2006.04.07)

Race condition vulnerability in sendmail [Updated 04/07/06 0849 CDT]

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IBM SECURITY ADVISORY


First Issued: Tue Mar 22 10:00:00 CST 2006
|Updated: Fri Apr  7 08:49:54 CDT 2006
|Updated ifix information
|Added prerequisites to ifixes
==========================================================================
                           VULNERABILITY SUMMARY

VULNERABILITY:      A race condition in sendmail may allow a remote
                    attacker to execute arbitrary code.

PLATFORMS:          AIX 5.1, 5.2 and 5.3.

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

THREAT:             A remote user may execute arbitrary code.

CERT VU Number:     CVE-2006-0058
CVE Number:         VU#834865
=========================================================================
                           DETAILED INFORMATION


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

A vulnerability was discovered in sendmail that may allow a remote attacker
to execute arbitrary code. This vulnerability is caused by a race condition
that occurs when handling asynchronous signals. Sendmail is a Mail Transfer
Agent that ships with the AIX operating system. It is used for routing mail
for local and network delivery. IBM is providing patches that remove
possible attack vectors for this vulnerability. These patches should be
installed as a precautionary measure.

sendmail ships as part of the bos.net.tcp.client fileset.


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

A remote attacker may execute arbitrary code with the privileges of the
sendmail daemon. By default, sendmail runs with the privileges of the root
user.


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

A. Official Fix

IBM provides the following fixes:


      APAR number for AIX 5.1.0:  IY82992 (available approx. 07/19/06)
      APAR number for AIX 5.2.0:  IY82993 (available approx. 04/26/06)
      APAR number for AIX 5.3.0:  IY82994 (available approx. 05/10/06)

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:

    ftp://aix.software.ibm.com/aix/efixes/security/sendmail_vu834865.tar.Z

sendmail_vu834865.tar.Z is a compressed tarball containing this advisory,
ifix packages and cleartext PGP signatures for each ifix 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:

|Updated: Fri Apr  7 08:49:54 CDT 2006
|Updated ifix information
|Added prerequisites to ifixes
|
|The interim fixes below have been updated to 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 the
|previous fixes released with this advisory. These updated fixes were
|released as a precaution to prevent the wrong fix from being installed on a
|Technology Level. Users that are certain they have applied the correct
|fixes to Technology Levels need not apply these fixes.
|
|
|Filename                  sum           md5
|========================================================================
|IY82992_09.060327.epkg.Z  15704   596   8b68183c9941ae3808ecdbc53eaa1e55
|IY82993_06.060327.epkg.Z  53675   567   7eaec7e0b48611bbff5bc020f70878a7 
|IY82993_07.060327.epkg.Z  63328   567   89805242db6c2cdcd394581f190b122e
|IY82993_08.060327.epkg.Z  32364   568   77fd23289ffa110cd90702ac154f0ec1
|IY82994_02.060327.epkg.Z  16561   587   93919f6db159d238c3ec7d49261dc3ba
|IY82994_03.060327.epkg.Z  37040   586   1cb862bd4f407a8cd257e38cefcf5b9b
|IY82994_04.060327.epkg.Z  29659   586   7a30afdb9fa948287879f911b210bee9

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@xxxxxxxxxxxxxx
and describe the discrepancy.


|Updated: Fri Apr  7 08:49:54 CDT 2006
|Updated ifix information
|Added prerequisites to ifixes
|
|
|The following table shows the prerequisite lower and upper fileset levels
|for the fixes above. These levels are inclusive and apply to
|bos.net.tcp.client.
|
|Filename                    Lower Level     Upper Level
|=========================================================
|IY82992_09.060327.epkg.Z    5.1.0.68        5.1.0.69
|IY82993_06.060327.epkg.Z    5.2.0.60        5.2.0.62
|IY82993_07.060327.epkg.Z    5.2.0.75        5.2.0.77
|IY82993_08.060327.epkg.Z    5.2.0.85        5.2.0.86
|IY82994_02.060327.epkg.Z    5.3.0.20        5.3.0.22
|IY82994_03.060327.epkg.Z    5.3.0.30        5.3.0.32
|IY82994_04.060327.epkg.Z    5.3.0.40        5.3.0.41


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

     http://www14.software.ibm.com/webapp/set2/sas/f/aix.efixmgmt/home.html

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
script.


Modify sendmail.cf
+----------------
Setting LogLevel to 1 in /etc/sendmail.cf will eliminate some attack vectors
for this vulnerability.


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

AIX Version 5 APARs can be downloaded from:

     http://www.ibm.com/servers/eserver/support/unixservers/aixfixes.html

Security related Interim 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:

     http://www14.software.ibm.com/webapp/set2/subscriptions/pqvcmjd

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

     security-alert@xxxxxxxxxxxxxx

To request the PGP public key that can be used to communicate securely
with the AIX Security Team send email to security-alert@xxxxxxxxxxxxxx
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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UNIRAS wishes to acknowledge the contributions of IBM for the information 
contained in this Briefing. 
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This Briefing contains the information released by the original author. Some 
of the information may have changed since it was released. If the vulnerability 
affects you, it may be prudent to retrieve the advisory from the site of the
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