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             AUSCERT External Security Bulletin Redistribution

                   ESB-2004.0721 -- UNIRAS ALERT - 40/04
        Vulnerability Issues in Implementations of the DNS Protocol
                             11 November 2004

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        AusCERT Security Bulletin Summary
        ---------------------------------

Publisher:         UNIRAS
Impact:            Denial of Service
Access:            Remote/Unauthenticated
CVE Names:         CAN-2004-0789

Original Bulletin: http://www.uniras.gov.uk/vuls/2004/758884/index.htm

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      UNIRAS (UK Govt CERT) ALERT - 40/04 dated 09.11.04  Time: 12:00  
 UNIRAS is part of NISCC (National Infrastructure Security Co-ordination Centre)
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  UNIRAS material is also available from its website at www.uniras.gov.uk and
         Information about NISCC is available from www.niscc.gov.uk
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Title
=====

Vulnerability Issues in Implementations of the DNS Protocol

Detail
====== 


NISCC Vulnerability Advisory 758884/NISCC/DNS
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Vulnerability Issues in Implementations of the DNS Protocol

Version Information
- - -------------------
Advisory Reference	758884/NISCC/DNS
Release Date		9 November 2004
Last Revision		4 November 2004
Version Number		1.0

What is affected?
- - -----------------
The vulnerabilities described in this advisory affect the Domain Name System (DNS) 
protocol. Many vendors include support for this protocol in their products and may be 
impacted to varying degrees, if at all.  

Please note that the information contained within this advisory is subject to 
changes. All subscribers are therefore advised to regularly check the UNIRAS website 
for updates to this notice.

Severity 
- - --------
The severity of these vulnerabilities varies by vendor. Please see the vendor section 
below for further information. Alternatively contact your vendor for product specific 
information. 

If exploited, these vulnerabilities could allow an attacker to create a Denial of 
Service condition.

Summary
- - -------
Several vulnerabilities have been discovered within the Domain Name System (DNS) 
protocol by two DNS experts, Roy Arends and Jakob Schlyter.

The Domain Name System (DNS) protocol is an Internet service that translates domain 
names into Internet Protocol (IP) addresses. Because domain names are alphabetic, 
they're easier to remember, however the Internet is really based on IP addresses; 
hence every time a domain name is requested, a DNS service must translate the name 
into the corresponding IP address.

NISCC wishes to advise users of the availability of a test tool that is designed to 
confirm the existence of vulnerabilities in the DNS protocol.

All users of applications that supports DNS are recommended to take note of this 
advisory and carry out any remedial actions suggested by their vendor(s).

[Please note that revisions to this advisory will not be notified by email.  All 
subscribers are advised to regularly check the UNIRAS website for updates to this 
notice.]

Details
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The Domain Name System (DNS) is basically a database of host information. The DNS 
protocol is utilised to identify servers by their IP addresses and aliases given their 
registered domain name. The request is usually simple, including just the name of the 
server. The response however can be quite complex, because it will contain all the 
addresses and aliases that the server might have. A DNS query is sent to a name server 
to provoke a response; a DNS response then either answers the query, refers 
the requester to another set of name servers or signals some error condition. Please 
refer to RFC 1034:Section 3.7, RFC 1034:Section 4.1, RFC 1034:Section 4.3.1 and 
RFC 1035:Section 4.1.1 for further information on the query-response relationship 
within the DNS protocol.

The relevant vulnerabilities are a result of liberal interpretation of the DNS protocol 
by implementors. DNS uses a message format to provide a mechanism to resolve 
domain names into IP addresses; a message can either be a 'query' or a 'response'. By 
implementating the protocol in such a way in which a 'response' is allowed to be
answered with a 'response', this will cause messages to bounce back and forth 
between the servers and hence cause a query-respose storm that can result in a 
denial-of-service attack.

In addition, by sending these implementations a query that appears to originate from the 
localhost on UDP port 53, the server will respond to itself and will keep 
responding to these responses, hence entering a loop which can exhaust system 
resources and hence result in a denial-of-service attack.

Further detail will be released as it becomes available.

This vulnerability has been assigned the CVE name CAN-2004-0789.

Solution
- - --------
Please refer to the Vendor Information section of this advisory for platform specific 
remediation.

Vendor Information
- - ------------------
A list of vendors affected by this vulnerability is not currently available. Please 
visit the web site at http://www.uniras.gov.uk/vuls/2004/758884/index.htm in order to 
check for updates.

Credits
- - -------
The NISCC Vulnerability Team would like to thank Roy Arends, who discovered this issue and 
reported it to NISCC, and Jakob Schlyter, who helped establish the initial list of 
vulnerable implementations. 

The NISCC Vulnerability Team would also like to thank the vendors for their co-operation 
in handling this vulnerability.

Contact Information
- - -------------------
The NISCC Vulnerability Management Team can be contacted as follows:

Email	   vulteam@niscc.gov.uk 
           Please quote the advisory reference in the subject line

Telephone  +44 (0)870 487 0748 Ext 4511
           Monday - Friday 08:30 - 17:00

Fax	   +44 (0)870 487 0749

Post	   Vulnerability Management Team
           NISCC
           PO Box 832
           London
           SW1P 1BG

We encourage those who wish to communicate via email to make use of our PGP key.  This 
is available from http://www.uniras.gov.uk/UNIRAS.asc 

Please note that UK government protectively marked material should not be sent to the 
email address above. 

If you wish to be added to our email distribution list please email your request to 
uniras@niscc.gov.uk.
 
What is NISCC?
- - --------------
For further information regarding the UK National Infrastructure Security Co-ordination 
Centre, please visit http://www.niscc.gov.uk/aboutniscc/index.htm.
 
Reference to any specific commercial product, process, or service by trade name, 
trademark manufacturer, or otherwise, does not constitute or imply its endorsement, 
recommendation, or favouring by NISCC. The views and opinions of authors expressed 
within this notice shall not be used for advertising or product endorsement purposes.

Neither shall NISCC accept responsibility for any errors or omissions contained within 
this advisory. In particular, they shall not be liable for any loss or damage 
whatsoever, arising from or in connection with the usage of information contained 
within this notice.

C 2004 Crown Copyright 

<End of NISCC Vulnerability Advisory>
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For additional information or assistance, please contact the HELP Desk by 
telephone or Not Protectively Marked information may be sent via 
EMail to: uniras@niscc.gov.uk

Office Hours:

Mon - Fri: 08:30 - 17:00 Hrs
Tel: +44 (0) 870 487 0748 Ext 4511
Fax: +44 (0) 870 487 0749

Outside of Office Hours:
On Call Duty Officer:
Tel: +44 (0) 870 487 0748 and follow the prompts

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UNIRAS wishes to acknowledge the contributions of Roy Arends and Jakob Schlyter for the information 
contained in this Briefing. 
- - ----------------------------------------------------------------------------------
This Briefing contains the information released by the original author. Some 
of the information may have changed since it was released. If the vulnerability 
affects you, it may be prudent to retrieve the advisory from the canonical site 
to ensure that you receive the most current information concerning that problem.

Reference to any specific commercial product, process, or service by trade 
name, trademark manufacturer, or otherwise, does not constitute or imply 
its endorsement, recommendation, or favouring by UNIRAS or NISCC.  The views 
and opinions of authors expressed within this notice shall not be used for 
advertising or product endorsement purposes.

Neither UNIRAS or NISCC shall also accept responsibility for any errors 
or omissions contained within this briefing notice. In particular, they shall 
not be liable for any loss or damage whatsoever, arising from or in connection 
with the usage of information contained within this notice.

UNIRAS is a member of the Forum of Incident Response and Security Teams (FIRST) 
and has contacts with other international Incident Response Teams (IRTs) in 
order to foster cooperation and coordination in incident prevention, to prompt 
rapid reaction to incidents, and to promote information sharing amongst its 
members and the community at large. 
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<End of UNIRAS Briefing>

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