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CERT(sm) Advisory CA-96.02
Original issue date:   February 15, 1996
Last revised: August 13, 1997
              Superseded by CA-97.22

              A complete revision history is at the end of this advisory.

Topic: BIND Version 4.9.3
- -----------------------------------------------------------------------------
            ** This advisory has been superseded by CA-97.22.bind **

Vulnerabilities in the Berkeley Internet Name Domain (BIND) program make it
possible for intruders to render Domain Name System (DNS) information
unreliable. At the beginning of this year, a version of BIND (4.9.3) became
available that fixes several security problems that are being exploited by
the intruder community.

The CERT staff urges you to install the appropriate patch from your vendor. If
a patch is not currently available, an alternative is to install BIND 4.9.3
yourself. (Note: Although BIND will be further improved in the future, we urge
you to upgrade now because of the seriousness of the problems addressed by
version 4.9.3.) If neither of the above alternatives is possible, we strongly
recommend blocking or turning off DNS name-based authentication services such
as rlogin.

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

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

I.   Description

     Version 4.9.3 of the Berkeley Internet Name Domain (BIND) program
     fixes several security problems that are well known and being
     exploited by the intruder community to render Domain Name System (DNS)
     information unreliable.

     BIND is an implementation of the Domain Name System. (For details,
     see RFC 1035, a publication of the Internet Engineering Task Force.)
     The full distribution of BIND includes a number of programs and resolver
     library routines. The main program is "named", the daemon that provides
     DNS information from local configuration files and a local cache. The
     named daemon is often called /etc/named or /etc/in.named. Programs such
     as Telnet communicate with named via the resolver library routines
     provided in the BIND distribution.

     Services in widespread use that depend on DNS information for
     authentication include rlogin, rsh (rcp), xhost, and NFS. Sites may
     have installed locally other services that trust DNS information.
     In addition, many other services, such as Telnet, FTP, and email,
     trust DNS information. If these services are used only to make outbound
     connections or informational logs about the source of connections, the
     security impact is less severe than for services such as rlogin. Although
     you might be willing to accept the risks associated with using these
     services for now, you need to consider the impact that spoofed DNS
     information may have.

     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.

     The CERT staff has received information that the next minor
     release of BIND nameserver will be enforcing RFC952 (as modified
     by RFC1123) hostname conformance as part of its SECURITY
     measures. Following The BIND release, hostnames that fail to
     conform to these rules will be unreachable from sites running
     these servers.

     Hostnames (A records) are restricted to the following characters only:

            "A" - "Z", "a" - "z", "0" - "9", "." and "-"

     These characters are specifically excluded:  "_" and "/".

     For a full description of what is allowed in a hostname, please
     refer to RFC952 and RFC1123, available from

        RFC1123: Requirements for Internet Hosts -- Application and
                        Support, October 1989

     A program is available for checking hostnames and IP addresses.
     It is available in

     The following files are in the directory (from the README):

IsValid.l       The lex/flex file containing the code for
                IsValidHostname and IsValidIPAddress
                MD5 (IsValid.l) = 2d35040aacae4fb12906eb1b48957776

IsValid-raw.c   The C file created by running flex
                on IsValid.l
                MD5 (IsValid-raw.c) = 367c77d3ef84bc63a5c23d90eeb69330

IsValid.c       The editted file created by internalizing
                variable and function definitions in
                MD5 (IsValid.c) = ffe45f1256210aeb71691f4f7cdad27f

IsValid.diffs   The set of diffs between IsValid-raw.c
                and IsValid.c
                MD5 (IsValid.diffs) = 3619022cf31d735151f8e8c83cce3744

htest.c         A main routing for testing IsValidHostname
                and IsValidIPAddress
                MD5 (htest.c) = 2d50b2bffb537cc4e637dd1f07a187f4

II.  Impact

     It is possible for intruders to spoof BIND into providing incorrect
     name data. Some systems and programs depend on this information for
     authentication, so it is possible to spoof those systems and gain
     unauthorized access.

III. Solutions

     The preferred solution, described in Section A, is to install your
     vendor's patch if one is available. An alternative (Section B) is to
     install the latest version of BIND. In both cases, we encourage you to
     take the additional precautions described in Section C.

  A. Obtain the appropriate patch from your vendor and install it according to
     instructions included with the program.

     Redistributing BIND and all programs affected by these problems is not
     a simple matter, so some vendors are working on new named daemon as an
     immediate patch. Although installing a new named daemon addresses some
     problems, significant problems remain that can be addressed only by
     fully installing fixes to the library resolver routines.

     If your vendor's patch does not include both named and new resolver
     routines, we recommend that you install the current version of BIND
     (Solution B) if possible. We also encourage you to take the precautions
     described in Section C.

     Below is a list of the vendors and the status they have provided
     concerning BIND. More complete information is provided in Appendix A
     of this advisory. We will update the appendix as we receive more
     information from vendors.

     If your vendor's name is not on the list, contact the vendor directly for
     status information and further instructions.

Vendor             New named available  Full distribution available
- ------             -------------------   ---------------------------
Digital Equipment                         Work is under way.
Hewlett-Packard    Under investigation.   Currently porting and testing
                                          (BIND 4.9.3) for the Q1, Calendar 97
                                          general release. Patch in process
                                          for 10.X releases.
IBM Corporation                           Work is under way.
NEC Corporation                           Work is under way.
Santa Cruz Operation                      Under consideration.
Silicon Graphics, Inc.                    Under investigation.
Solbourne (Grumman)                       Customers should install BIND 4.9.3.
Sun Microsystems                          Patches available.

  B. Install the latest version of BIND (version 4.9.3), available from Paul
     Vixie, the current maintainer of BIND:

         MD5 (bind-4.9.3-REL.tar.gz) = da1908b001f8e6dc93fe02589b989ef1

      Also get Patch #1 for 4.9.3:

         MD5 (Patch1) = 5d57ad13381e242cb08b5da0e1e9c5b9

     To find the most current version of bind, see

  C. Take additional precautions.

     To protect against vulnerabilities that have not yet been addressed, and
     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

Below is information we have received from vendors. If you do not see an
entry for your vendor, please contact the vendor directly for status
information and further instructions.

- ---------------------------------------
Paul Vixie

        See Updates Section

- ---------------------------------------
Digital Equipment Corporation

At the time of writing this advisory, Digital intends to support the final
revision of BIND 4.9.3. The project plan for incorporating Version 4.9.3 BIND
for Digital's ULTRIX platforms has been approved. This includes 4.3, V4.3A,
V4.4 and V4.5.

A similar project plan for Digital UNIX versions is under review. The first
implementations will be V3.0 through V3.2D, and V4.0, when released. It is our
plan to evaluate and then incorporate V4.9.3 Bind into other UNIX versions as
necessary to reduce risk to our customer base.

Digital will provide notice of the completion of the kits through AES services
(DIA, DSNlink FLASH) and be available from your normal Digital Support

- ---------------------------------------
Hewlett-Packard Company

The named daemon is under investigation. HP will provide updated
information for the CERT advisory.

HP is currently porting and testing BIND 4.9.3 for a general release
first quarter of 1997. A patch is in process for 10.X releases. Watch
for CERT advisory updates and a Security Bulletin from HP.

- ---------------------------------------
IBM Corporation

Work is under way.

- ---------------------------------------
NEC Corporation

Some systems are vulnerable. We are developing the patches and plan to put
them on our anonymous FTP server. You can contact us with the following
e-mail address if you need.

FTP server:

- ---------------------------------------
The Santa Cruz Operation, Inc.

SCO is currently considering a port of the new BIND into its product line,
but no timeline is yet available. This includes SCO OpenServer and SCO

- ---------------------------------------
Silicon Graphics Inc.

SGI acknowledges CERT Advisory CA-96.02 and is currently investigating.
No further information is available at this time.

As further information becomes available, additional advisories will
be available from

- ---------------------------------------
Solbourne (Grumman)

Solbourne have determined that Solbourne Computers are vulnerable.
A patch is not available and they recommend Solbourne customers install
BIND version 4.9.3.

- ---------------------------------------
Sun Microsystems, Inc.

Sun Security Patches and Bulletins are available through your local
SunService and SunSoft Support Services organizations, via the
security-alert alias ( and on SunSolve

SunOS 5.3/Solaris 2.3
- ---------------------
        101359-03       SunOS 5.3: DNS spoofing is possible per CERT CA-96.02
        101739-12       sendmail patch
        102167-03 rebuild for BIND 4.9.3
        103705-01       rpc.nisd_resolv rebuild for BIND 4.9.3

SunOS 5.4/Solaris 2.4
- ---------------------
        102479-02       SunOS 5.4: DNS spoofing is possible per CERT CA-96.02
        102066-11       sendmail patch
        102165-03 rebuild for BIND 4.9.3
        103706-01       rpc.nisd_resolv rebuild for BIND 4.9.3

SunOS 5.4_x86/Solaris 2.4_x86
- -----------------------------
        102480-02       SunOS 5.4_x86: DNS spoofing is possible per
                          CERT CA-96.02
        102064-10       sendmail patch
        102166-03 rebuild for BIND 4.9.3
        103707-01       rpc.nisd_resolv rebuild for BIND 4.9.3

SunOS 5.5/Solaris 2.5
- ---------------------
        103667-01       SunOS 5.5: DNS spoofing is possible per CERT CA-96.02
        102980-07       sendmail patch
        103279-02       nscd/nscd_nischeck rebuild for BIND 4.9.3
        103703-01 rebuild for BIND 4.9.3
        103708-01       rpc.nisd_resolv rebuild for BIND 4.9.3

SunOS 5.5_x86/Solaris 2.5_x86
- -----------------------------
        103668-01       SunOS 5.5_x86: DNS spoofing is possible per
                          CERT CA-96.02
        102981-07       sendmail patch
        103280-02       nscd/nscd_nischeck rebuild for BIND 4.9.3
        103704-01 rebuild for BIND 4.9.3
        103709-01       rpc.nisd_resolv rebuild for BIND 4.9.3

SunOS 5.5.1/Solaris 2.5.1
- -------------------------
        103663-01       SunOS 5.5.1: DNS spoofing is possible per CERT CA-96.02
        103594-03       sendmail patch
        103680-01       nscd/nscd_nischeck rebuild for BIND 4.9.3
        103683-01 rebuild for BIND 4.9.3
        103686-01       rpc.nisd_resolv rebuild for BIND 4.9.3

SunOS 5.5.1_ppc/Solaris 2.5.1_ppc
- ---------------------------------
        103665-01       SunOS 5.5.1_ppc: DNS spoofing is possible per
                          CERT CA-96.02
        103596-03       sendmail patch
        103682-01       nscd/nscd_nischeck rebuild for BIND 4.9.3
        103685-01 rebuild for BIND 4.9.3
        103688-01       rpc.nisd_resolv rebuild for BIND 4.9.3

SunOS 5.5.1_x86/Solaris 2.5.1_x86
- ---------------------------------
        103664-01       SunOS 5.5.1_x86: DNS spoofing is possible per
                          CERT CA-96.02
        103595-03       sendmail patch
        103681-01       nscd/nscd_nischeck rebuild for BIND 4.9.3
        103684-01 rebuild for BIND 4.9.3
        103687-01       rpc.nisd_resolv rebuild for BIND 4.9.3

- ---------------------------------------------------------------------------
The CERT Coordination Center wishes to thank Paul Vixie for his efforts in
responding to this problem and his aid in developing this advisory.
- ---------------------------------------------------------------------------

If you believe that your system has been compromised, contact the CERT
Coordination Center or your representative in the Forum of Incident
Response and Security Teams (FIRST).

We strongly urge you to encrypt any sensitive information you send by email.
The CERT Coordination Center can support a shared DES key and PGP. Contact the
CERT staff for more information.

Location of CERT PGP key

CERT Contact Information
- ------------------------

Phone    +1 412-268-7090 (24-hour hotline)
                CERT personnel answer 8:30-5:00 p.m. EST
                (GMT-5)/EDT(GMT-4), and are on call for
                emergencies during other hours.

Fax      +1 412-268-6989

Postal address
        CERT Coordination Center
        Software Engineering Institute
        Carnegie Mellon University
        Pittsburgh PA 15213-3890

To be added to our mailing list for CERT advisories and bulletins, send your
email address to

CERT publications, information about FIRST representatives, and other
security-related information are available for anonymous FTP from

CERT advisories and bulletins are also posted on the USENET newsgroup

Copyright 1996 Carnegie Mellon University
This material may be reproduced and distributed without permission provided it
is used for noncommercial purposes and the copyright statement is included.

CERT is a service mark of Carnegie Mellon University.


June 25, 1997
- -------------

If you are running BIND 8.1 you want to upgrade. The current version
of BIND (8.8.1) is available by anonymous FTP from

If you are still running BIND-4 rather than BIND-8, you need the
security patches contained in BIND 4.9.6. Available from

The author of BIND encourages sites to switch to BIND-8.

Revision History

Aug. 13, 1997  This advisory superseded by CA-97.22.
June 25, 1997  Appendix, Changed Vixie entry to point to Updates.
               Updates section - Current release information.
May 22, 1997  Updates section - noted current version of BIND and new location
                                for the BIND archives.
Aug. 30, 1996  Information previously in the README was inserted into the
Aug. 01, 1996  Appendix - updated Sun patch information
Apr. 08, 1996  Sec. I - added information about the next release of BIND
               and the IsValid program to the end of the section
Mar. 29, 1996  Appendix, Sun - added information
Feb. 27, 1996  Appendix, SGI - added an entry
Feb. 21, 1996  Appendix, IBM & Solbourne - added entries

Version: PGP for Personal Privacy 5.0
Charset: noconv


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