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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
   to:

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

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

Overview

   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:

     http://www.kb.cert.org/vuls/id/803539

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

     http://www.kb.cert.org/vuls/id/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.

     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
   comments.

Compaq

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

     x-ref:SSRT2270

     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
     problem.

FreeBSD

     See
     ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-02:28.
     resolv.asc

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:

     http://www.gnu.org/software/adns/
     http://www.chiark.greenend.org.uk/~ian/adns/

Internet Software Consortium

     All versions of BIND 4 from 4.8.3 prior to BIND 4.9.9 are
     vulnerable.
     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:

     ftp://ftp.isc.org/isc/bind/src/4.9.9/
     ftp://ftp.isc.org/isc/bind/src/8.2.6/
     ftp://ftp.isc.org/isc/bind/src/8.3.3/
     ftp://ftp.isc.org/isc/bind/contrib/ntbind-8.3.3/

     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
     8.3.3.

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

     Vendors wishing additional patches should contact
     bind-bugsisc.org.
     Query about BIND 4 and BIND 8 should be addressed to
     bind-bugsisc.org.
     Query about BIND 9 should be addressed to bind9-bugsisc.org.

Microsoft

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

OpenBSD

     [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
     different.

NetBSD

     See
     ftp://ftp.NetBSD.ORG/pub/NetBSD/security/advisories/NetBSD-SA2002-0
     06.txt.asc

Network Appliance

     Some NetApp systems are vulnerable to this problem. Check NOW
     (http://now.netapp.com) for information on whether your system is
     vulnerable and the appropriate patch release that you should
     install.

SGI

     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.
   Rafail
     _________________________________________________________________

Appendix B. - References

    1. http://www.pine.nl/advisories/pine-cert-20020601.asc

   ______________________________________________________________________

   This document is available from:
   http://www.cert.org/advisories/CA-2002-19.html
   ______________________________________________________________________

CERT/CC Contact Information

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Revision History

   June 28, 2002: Initial release

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