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Home : Advisories : Two DoS Vulnerabilities in BIND

Title: Two DoS Vulnerabilities in BIND
Released by: IBM Global Services
Date: 27th November 2000
Printable version: Click here
                            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:


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".

If you would like to subscribe to the AIX security newsletter, send a

note to aixserv@austin.ibm.com 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


IBM and AIX are a registered trademark of International Business

Machines Corporation.  All other trademarks are property of their

respective holders.


Version: PGP Personal Privacy 6.5.3








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Copyright 2000 International Business Machines Corporation.

The information in this document is provided as a service to customers of

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