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HistoryJun 29, 2002 - 12:00 a.m.

Advisory 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
 [email protected].
 Query   about   BIND   4   and   BIND  8  should  be  addressed  to
 [email protected].
 Query about BIND 9 should be addressed to [email protected].


 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