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CA-2002-19 Buffer Overflow in Multiple DNS Resolver Libraries


CERT Advisory CA-2002-19 Buffer Overflow in Multiple DNS Resolver Libraries

Original release date: June 28, 2002
Last revised: --
Source: CERT/CC

A complete revision history can be found at the end of this file.

Systems Affected

Applications using vulnerable implementations of the Domain Name
System (DNS) resolver libraries, which include, but are not limited

* Internet Software Consortium (ISC) Berkeley Internet Name Domain
(BIND) DNS resolver library (libbind)

* Berkeley Software Distribution (BSD) DNS resolver library (libc)


A buffer overflow vulnerability exists in multiple implementations of
DNS resolver libraries. Operating systems and applications that
utilize vulnerable DNS resolver libraries may be affected. A remote
attacker who is able to send malicious DNS responses could potentially
exploit this vulnerability to execute arbitrary code or cause a denial
of service on a vulnerable system.

I. Description

The DNS protocol provides name, address, and other information about
Internet Protocol (IP) networks and devices. To access DNS
information, a network application uses the resolver to perform DNS
queries on its behalf. Resolver functionality is commonly implemented
in libraries that are included with operating systems.

Multiple implementations of DNS resolver libraries contain a remotely
exploitable buffer overflow vulnerability in the way the resolver
handles DNS responses. Both BSD (libc) and ISC (libbind) resolver
libraries share a common code base and are vulnerable to this problem;
any DNS resolver implementation that derives code from either of these
libraries may also be vulnerable. Network applications that makes use
of vulnerable resolver libraries are likely to be affected, therefore
this problem is not limited to DNS or BIND servers.

Vulnerability Note VU#803539 lists the vendors that have been
contacted about this vulnerability:

This vulnerability is not the same as the Sendmail issue discussed in
Vulnerability Note VU#814627:

II. Impact

An attacker who is able to send malicious DNS responses could remotely
exploit this vulnerability to execute arbitrary code or cause a denial
of service on vulnerable systems. Any code executed by the attacker
would run with the privileges of the process that calls the vulnerable
resolver function.

Note that an attacker could cause one of the victim's network services
to make a DNS request to a DNS server under the attacker's control.
This would permit the attacker to remotely exploit this vulnerability.

III. Solution

Upgrade to a corrected version of the DNS resolver libraries

Note that DNS resolver libraries can be used by multiple
applications on most systems. It may be necessary to upgrade or
apply multiple patches and then recompile statically linked

Applications that are statically linked must be recompiled using
patched resolver libraries. Applications that are dynamically
linked do not need to be recompiled; however, running services need
to be restarted in order to use the patched resolver libraries.

System administrators should consider the following process when
addressing this issue:

1. Patch or obtain updated resolver libraries.

2. Restart any dynamically linked services that make use of the
resolver libraries.

3. Recompile any statically linked applications using the patched or
updated resolver libraries.

Use a local caching DNS server

Using a local caching DNS server that reconstructs DNS responses
will prevent malicious responses from reaching systems using
vulnerable DNS resolver libraries. For example, BIND 9 reconstructs
responses in this way, with the exception of forwarded dynamic DNS
update messages. Note that BIND 8 does not reconstruct all
responses; therefore this workaround may not be effective when
using BIND 8 as a caching DNS server.

Appendix A. - Vendor Information

This appendix contains information provided by vendors for this
advisory. When vendors report new information to the CERT/CC, we
update this section and note the changes in our revision history. If a
particular vendor is not listed below, we have not received their


SOURCE: Compaq Computer Corporation, a wholly-owned subsidiary of
Hewlett-Packard Company and Hewlett-Packard Company HP Services
Software Security Response Team


At the time of writing this document, Compaq is currently
investigating the potential impact to Compaq's released Operating
System software products.

As further information becomes available Compaq will provide notice
of the completion/availibility of any necessary patches through
standard product and security bulletin announcements and be
available from your normal HP Services support channel.

Cray, Inc.

The DNS resolver code supplied by Cray, Inc. in Unicos and
Unicos/mk is vulnerable. SPR 722619 has been opened to track this



GNU adns

adns is not derived from BIND libresolv. Furthermore, it does not
support a gethostbyname-like interface (which is where the bug in
BIND libresolv is). Therefore, it is not vulnerable.

For more information on GNU adns, see:

Internet Software Consortium

All versions of BIND 4 from 4.8.3 prior to BIND 4.9.9 are
All versions of BIND 8 prior to BIND 8.2.6 are vulnerable.
All versions of BIND 8.3.x prior to BIND 8.3.3 are vulnerable.
BIND versions BIND 9.2.0 and BIND 9.2.1 are vulnerable.
BIND version 4.8 does not appear to be vulnerable.
BIND versions BIND 9.0.x and BIND 9.1.x are not vulnerable.
'named' itself is not vulnerable.
Updated releases can be found at:

BIND 9 contains a copy of the BIND 8.3.x resolver library
(lib/bind). This will be updated with the next BIND 9 releases
(9.2.2/9.3.0) in the meantime please use the original in BIND

In addition the BIND 9 'named' can be used to prevent malformed
answers reaching vulnerable clients.

Vendors wishing additional patches should contact
Query about BIND 4 and BIND 8 should be addressed to
Query about BIND 9 should be addressed to


Microsoft products do not use the libraries in question. Microsoft
products are not affected by this issue.


[T]he resolver libraries in question got copied far and wide. They
used to have a hell of a lot of bugs in them.

Now might be a good time for people to compare each others'
libraries to each other. I would urge them to compare against the
OpenBSD ones, where we've spent a lot of time on, but of course we
still missed this. But perhaps people can then share some around.
Not everyone is going to move to the bind9 stuff, since it is very



Network Appliance

Some NetApp systems are vulnerable to this problem. Check NOW
( for information on whether your system is
vulnerable and the appropriate patch release that you should


SGI is looking into the matter.


The CERT Coordination Center thanks Joost Pol of PINE-CERT and the
FreeBSD Project for their analysis of these vulnerabilities.

Feedback can be directed to the authors: Art Manion and Jason A.

Appendix B. - References



This document is available from:

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Revision History

June 28, 2002: Initial release

Version: PGP 6.5.8


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