||Home : Advisories : Two DoS Vulnerabilities in BIND|
||Two DoS Vulnerabilities in BIND
||IBM Global Services
||27th November 2000
IBM Global Services
Emergency Response Service
Security Vulnerability Alert
27 NOV 2000 11:30 GMT ERS-SVA-E01-2000:005.1
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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
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
Domain name resolution services can be completely negated on DNS
servers from remote systems.
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,
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 22.214.171.124 & bos.rte.libc is 126.96.36.199.
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
We recommend that backup copies of the original "libc.a" and the "named8"
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 "email@example.com" with the word "FixDist" in the
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 "firstname.lastname@example.org" with
the word "subscribe Security_APARs" in the "Subject:" line.
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 email@example.com
with a subject of "get key".
If you would like to subscribe to the AIX security newsletter, send a
note to firstname.lastname@example.org 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
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