IBM Global Services

                        Emergency Response Service

                       Security Vulnerability Alert



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

===========================================================================

-----BEGIN PGP SIGNED MESSAGE-----



                           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

    see



    http://www.isc.org/products/BIND/bind-security.html



    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

server.





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

      soon:



      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:



    http://aix.software.ibm.com/aix/efixes/security/named8_DoS_efix.tar.Z



    The MD5 checksums for the efix tarfiles are:



    Filename                sum             md5

    =================================================================

    named43Service.tar      29576  6880

7389bc7758a92f1fccb01fcadbf24166

    named43Sgold.tar        28101  6930

b266377a22f869ece15c4046a9827b2a



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

executables

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 4.3.3.25 & bos.rte.libc is 4.3.3.25.



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

these

commands:



# lslpp -l bos.rte.libc

# lslpp -l bos.net.tcp.server



Also, these e-fixes have not been fully regression tested. Customers

installing

and using these e-fixes do so at their own risk.





INSTALLATION STEPS:



- - - ----------------------------------------

Perform all steps given below as "root".

- - - ----------------------------------------



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

machine).



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

DNS/nameserver

   has.



2) mkdir /tmp/testnamed



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

/tmp/testnamed)



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"

files

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



        http://techsupport.services.ibm.com/rs6k/fixes.html



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".



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

"help".



IBM and AIX are a registered trademark of International Business

Machines Corporation.  All other trademarks are property of their

respective holders.

-----BEGIN PGP SIGNATURE-----

Version: PGP Personal Privacy 6.5.3



iQCVAwUBOiJUvfWDLGpfj4rlAQHVVgQAs5q9P/l3a64DE91C/V3sRKJOkcj3xP3c

7NUL1I0weiiv1CK2tJsoiLD7pVe9BxupTh6FVzXpHWo5/9RyhgnM/f2ej06nrNPY

ab3pE3SICKf5oKkuP045qpOOAkpCr2S7MxgCruIA1ZVH2R/2EfhPCtatGIEeoPPl

RK3cgq77KEs=

=uTcW

-----END PGP SIGNATURE-----

===========================================================================

IBM's Internet Emergency Response Service (IBM-ERS) is a subscription-based

Internet security response service that includes computer security incident

response and management, regular electronic verification of your Internet

gateway(s), and security vulnerability alerts similar to this one that are

tailored to your specific computing environment.  IBM's Virus Emergency

Response Service is a subscription-based service that provides assistance

with virus risk and emergency management.  By acting as an extension of

your own internal security staff, IBM-ERS's team of security experts helps

you quickly detect and respond to attacks and exposures to your I/T

infrastructre.



As a part of IBM's Business Continuity Recovery Services organization, the

IBM Emergency Response Service is a component of IBM's SecureWay(tm) line

of security products and services.  From hardware to software to

consulting, SecureWay solutions can give you the assurance and expertise

you need to protect your valuable business resources.  To find out more

about the IBM Emergency Response Service, send an electronic mail message

to ers-sales@ers.ibm.com, or call 1-800-426-7378.



IBM-ERS maintains a site on the World Wide Web at http://www.ers.ibm.com/.

Visit the site for information about the service, copies of security

alerts, team contact information, and other items.



IBM-ERS uses Pretty Good Privacy* (PGP*) as the digital signature mechanism

for security vulnerability alerts and other distributed information.  The

IBM-ERS PGP* public key is available from

http://www.ers.ibm.com/team-info/pgpkey.html.

"Pretty Good Privacy" and "PGP" are trademarks of Philip Zimmermann.



IBM-ERS is a Member Team of the Forum of Incident Response and Security

Teams (FIRST), a global organization established to foster cooperation and

response coordination among computer security teams worldwide.



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

accuracy, complete- ness, or usefulness of any information, apparatus,

product, or process contained herein, or represents that its use would not

infringe any privately owned rights.  Reference herein to any specific

commercial products, process, or service by trade name, trademark,

manufacturer, or otherwise, does not necessarily constitute or imply its

endorsement, recommendation or favoring by IBM or its subsidiaries.  The

views and opinions of authors expressed herein do not necessarily state or

reflect those of IBM or its subsidiaries, and may not be used for

advertising or product endorsement purposes.



The material in this security alert may be reproduced and distributed,

without permission, in whole or in part, by other security incident

response teams (both commercial and non-commercial), provided the above

copyright is kept intact and due credit is given to IBM-ERS.



This security alert may be reproduced and distributed, without permission,

in its entirety only, by any person provided such reproduction and/or

distribution is performed for non-commercial purposes and with the intent

of increasing the awareness of the Internet community.

===========================================================================