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  • CERT Advisory CA-1997-22 BIND - the Berkeley Internet Name Daemon

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Original issue date: August 13, 1997
Last revised: May 26, 1998
Updated vendor information for Sun Microsystems

A complete revision history is at the end of this file.
*** This advisory supersedes CA-96.02. ***

Several vulnerabilities in the Berkeley Internet Name Daemon (BIND) have been fixed in the current version of BIND. One of those vulnerabilities is now being exploited, a vulnerability that results in cache poisoning (malicious or misleading data from a remote name server is saved [cached] by another name server).

The vulnerability has been fixed in BIND version 4.9.6; however, we recommend upgrading according to our instructions in Section III.B or installing vendor patches (see Appendix A). We also urge you to take the additional precautions described in Section III.C.

We will update this advisory as we receive additional information. Please check our advisory files regularly for updates that relate to your site.

I. Description

The Berkeley Internet Name Daemon (BIND) is an implementation of the Domain Name Service (DNS) written primarily for UNIX Systems. BIND consists of three parts:

  • The client part. This part contains subroutine libraries used by programs that require DNS services. Example clients of these libraries are telnet, the X Windows System, and ssh (the secure shell). The client part consists of subroutine libraries, header files, and manual pages.

  • The server part. This part contains the name server daemon (named) and its support program (named-xfer). These programs provide one source of the data used for mapping between host names and IP addresses. When appropriately configured, these name server daemons can interoperate across a network (the Internet for example) to provide the mapping services for that network. The server part consists of the daemon, its support programs and scripts, and manual pages.

  • The tools part. This part contains various tools for interrogating name servers in a network. They use the client part to extract information from those servers. The tools part consists of these interrogation tools and manual pages.
As BIND has matured, several vulnerabilities in the client, server, and tools parts have been fixed. Among these is server cache poisoning. Cache poisoning occurs when malicious or misleading data received from a remote name server is saved (cached) by another name server. This "bad" data is then made available to programs that request the cached data through the client interface.

Analysis of recent incidents reported to the CERT Coordination Center has shown that the cache poisoning technique is being used to adversely affect the mapping between host names and IP addresses. Once this mapping has been changed, any information sent between hosts on a network may be subjected to inspection, capture, or corruption.

Although, the new BIND distributions do address important security problems, not all known problems are fixed. IN particular, several problems can be fixed only with the use of cryptographic authentication techniques. Implementing and deploying this solution is non-trivial; work on this task is currently underway within the Internet community.

II. Impact

The mapping between host names and IP addresses may be changed. As a result, attackers can inspect, capture, or corrupt the information exchanged between hosts on a network.

III. Solution

Install a patch from your vendor or implement the "best practice" workaround we recommend in Section III.B. In either case, take the extra precautions described in Section III.C.

A. Obtain and install a patch for this problem.

Information from vendors can be found in Appendix A of this advisory; we will update the appendix as we receive more information.

B. Until you are able to install the appropriate patch, we recommend the following workaround.

The "best practice" for operating the publicly available BIND system can be either:
  • a heterogeneous solution that involves first installing BIND release 4.9.6 and then release 8.1.1, or
  • a homogeneous solution that involves installing only BIND release 8.1.1.
In the paragraphs below, we describe how to determine which solution you should use.

Note: Although the security posture in BIND version 8.1.1 is identical to that of version 4.9.6, version 8.1.1 is the version that will continue to undergo changes and improvements, hence our selection of its use as the "best practice."

1. Shared Object Client Subroutine Library

If your system and its programs rely on the shared object client subroutine library that comes with some releases of BIND, probably named, then you need the shared object subroutine library and other client software from release 4.9.6. (As of this writing, BIND version 8 does not yet support the client part as a shared object library.) This client software is available at

MD5 (bind-4.9.6-REL.tar.gz) = 76dd66e920ad0638c8a37545a6531594

Follow the instructions in the file named INSTALL in the top-level directory.
After installing this client part, install the server and tool parts from release 8.1.1. This software is available at

MD5 (bind-src.tar.gz) = 7487b8d647edba2053edc1cda0c6afd0

Follow the instructions in the src/INSTALL file. Note that this version will install the client libraries and header files in a non-standard place, /usr/local/lib and /usr/local/include. The src/INSTALL file describes what is being installed and where.

When you install release 4.9.6 first, its client, server, and tools parts will be installed in the production locations. When you then install release 8.1.1, the server and tools parts will be overwritten by that release's versions, but the 4.9.6 client part will not.

2. No Shared Object Client Subroutine Library

If you do not need the shared object client subroutine library, then you need only upgrade to release 8.1.1. This software is available at

MD5 (bind-src.tar.gz) = 7487b8d647edba2053edc1cda0c6afd0

Follow the instructions in src/INSTALL. Note that the client subroutine library and header files are installed in /usr/local/lib and /usr/local/include respectively. To use these when building other systems, you will need to refer to their installed locations.

Note: is mirrored in Germany at

As new versions of BIND are released in the future, you will be able to find them at these sites, as well as other mirrors. You can also check for version information.

C. Take additional precautions.

As good security practice in general, filter at a router all name-based authentication services so that you do not rely on DNS information for authentication. This includes the services rlogin, rsh (rcp), xhost, NFS, and any other locally installed services that provide trust based on domain name information.

Appendix A - Vendor Information

Below is a list of the vendors who have provided information for this advisory. We will update this appendix as we receive additional information. If you do not see your vendor's name, the CERT/CC did not hear from that vendor. Please contact the vendor directly.

Berkeley Software Design, Inc. (BSDI)

Patches from BSDI
md5 checksum: 8ce46cd2d1aff3b294a84ae54e82a824
md5 checksum: d7b5c6094089955cd1af207dab05bc0f

Cray Research - A Silicon Graphics Company

Cray Research has determined that the version of BIND shipped with all current releases of Unicos and Unicos/mk are susceptible to the problem described in this advisory. We are currently working on upgrading our version of BIND to the 4.9.6 release.

Digital Equipment Corporation

xref CASE ID: SSRT0494U

At the time of writing this document, patches(binary kits) are in progress and final patch testing is expected to begin soon. Digital will provide notice of the completion/availability of the patches through AES services (DIA, DSNlink FLASH) and be available from your normal Digital Support channel.


Hewlett-Packard Company

HP is vulnerable. Patches in process.

IBM Corporation

IBM is currently working on the following APARs which will be available soon:

AIX 4.1: IX70236
AIX 4.2: IX70237

To Order

APARs may be ordered using Electronic Fix Distribution (via FixDist) or from the IBM Support Center. For more information on FixDist, reference URL:

or send e-mail to with a subject of "FixDist".

IBM and AIX are registered trademarks of International Business Machines Corporation.

NEC Corporation

NEC is vulnerable. The systems affected by this problem
are as follows:


Patches are in progress and will be made available from

Siemens-Nixdorf Informationssysteme AG

We are investigating this problem and will provide updated information for this advisory when it becomes available.

The Santa Cruz Operation

The following SCO operating systems are vulnerable:

- SCO Open Desktop/Open Server 3.0, SCO UNIX 3.2v4
- SCO OpenServer 5.0
- SCO UnixWare 2.1

SCO CMW+ 3.0 is not vulnerable as bind is not supported on CMW+ platforms.

SCO has made an interim fix available for anonymous ftp: - cover letter - replacement binaries

The fix includes binaries for the following SCO operating systems:

- SCO Open Desktop/Open Server 3.0, SCO UNIX 3.2v4
- SCO OpenServer 5.0
- SCO UnixWare 2.1

Sun Microsystems

The following patches relate to the BIND vulnerability:
        SunOS version   Patch Id
        -------------   --------
        5.6             105755-03
        5.6_x86         105756-03
        5.5.1           103663-11
        5.5.1_x86       103664-11
        5.5             103667-09
        5.5_x86         103668-09
        5.4             102479-11
        5.4_x86         102480-09
        5.3             101359-08
Sun recommended security patches (including checksums) are available from:

The CERT Coordination Center staff thanks Paul Vixie and Wolfgang Ley for their contributions to this advisory.

Copyright 1997 Carnegie Mellon University.

Revision History
May 26, 1998  Updated vendor information for Sun Microsystems
Sept. 30, 1997 Updated copyright statement
Sept. 19, 1997 Appendix A - Added information for BSDI.
Aug. 20, 1997 Introduction - Clarified that 4.9.6 is not vulnerable.
 Section III - Added a note why sites should upgrade to 8.1.1.
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