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IBM-ERS Security Vulnerability Alert: IBM AIX: Two DoS Vulnerabilities in BIND
From: IGS ERS Advisory Service <advisory () US IBM COM>
Date: Mon, 27 Nov 2000 09:16:32 -0500

                            IBM Global Services
                        Emergency Response Service
                       Security Vulnerability Alert

27 NOV 2000  11:30 GMT                             ERS-SVA-E01-2000:005.1

                           VULNERABILITY SUMMARY

VULNERABILITY:    Two DoS Vulnerabilities in BIND

PLATFORMS:        IBM AIX 4.2.x, 4.3.x

SOLUTION:         Apply the fixes listed below.

THREAT:           DNS can be completely disrupted on affected servers.

CERT Advisory:    CA-2000-20

                           DETAILED INFORMATION

I.  Description

    The Internet Software Consortium, the maintainer of BIND, the software
    used to provide domain name resolution services, has recently posted
    information about several denial-of-service vulnerabilities. If
    exploited, any of these vulnerabilities could allow remote intruders
    to cause site DNS services to be stopped.

    For more information about these vulnerabilities, please


    Two vulnerabilities in particular are especially serious:
The "zxfr bug"

    Using this vulnerability, attackers on sites which are permitted to
    request zone transfers can force the named daemon running on
    vulnerable DNS servers to crash, disrupting name resolution service
    until the named daemon is restarted. The only preconditions for this
    attack to succeed is that a compressed zone transfer (ZXFR) request be
    made from a site allowed to make any zone transfer request (not just
    ZXFR), and that a subsequent name service query of an authoritative
    and non-cached record be made. The time between the attack and the
    crash of named may vary from system to system.

    This vulnerability has been discussed in public forums. The ISC has
    confirmed that all platforms running version 8.2.2 of the BIND
    software prior to patch level 7 are vulnerable to this attack.

The "srv bug"

    This vulnerability can cause affected DNS servers running named to go
    into an infinite loop, thus preventing further name requests to be
    handled. This can happen if an SRV record is sent to the vulnerable

II.  Impact

     Domain name resolution services can be completely negated on DNS
     servers from remote systems.

II.  Solutions

  A.  Official fix

      IBM is working on the following fix which will be available

      AIX 4.3.x:  APAR IY14512

      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, or higher.

  B.  How to minimize the vulnerability

    A temporary fix for AIX 4.3.x systems is available.

    The temporary fix can be downloaded via ftp from:


    The MD5 checksums for the efix tarfiles are:

    Filename                sum             md5
    named43Service.tar      29576  6880
    named43Sgold.tar        28101  6930

This e-fix contains two tarfiles: named43Service.tar and named43Sgold.tar,
each of
which contains the files libc.a, named8, and named8-xfer. These are the
you will need. Choose the tarfile most appropriate for your site.

IMPORTANT NOTICE: Your operating system MUST be at this level for the e-fix
to work properly and to keep your machines properly operating:
fileset bos.net.tcp.server is & bos.rte.libc is

You can determine what level your system is at by examining the output from

# lslpp -l bos.rte.libc
# lslpp -l bos.net.tcp.server

Also, these e-fixes have not been fully regression tested. Customers
and using these e-fixes do so at their own risk.


- - - ----------------------------------------
Perform all steps given below as "root".
- - - ----------------------------------------

NOTICE: Test this e-fix FIRST on a test machine (i.e. non-production

1) Setup the test machine with the same data as your production

2) mkdir /tmp/testnamed

3) cp named43Sgold.tar /tmp/testnamed  (or cp named43Sservice.tar

4) cd /tmp/testnamed

5) tar -xvf *tar

6) mount libc.a /usr/lib/libc.a

7) mount named8 /usr/sbin/named8

8) mount named8-xfer /usr/sbin/named8-xfer

9) startsrc -s named

10) Run some tests to verify the name server's proper operation.

11) If all the tests are successful, then repeat the above on the
production machine.

We recommend that backup copies of the original "libc.a" and the "named8"
be made.

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


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.  Acknowledgements

Thanks to the correspondents to BUGTRAQ and the CERT/CC for bringing
this vulnerability to our attention.

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".

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IBM's Internet Emergency Response Service (IBM-ERS) is a subscription-based
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tailored to your specific computing environment.  IBM's Virus Emergency
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Copyright 2000 International Business Machines Corporation.

The information in this document is provided as a service to customers of
the IBM Emergency Response Service.  Neither International Business
Machines Corporation, nor any of its employees, makes any warranty, express
or implied, or assumes any legal liability or responsibility for the
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The material in this security alert may be reproduced and distributed,
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