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National Cyber Alert System
Technical Cyber Security Alert TA08-190B
Multiple DNS implementations vulnerable to cache poisoning
Original release date: July 08, 2008
Last revised: --
Source: US-CERT
Systems Affected
Systems implementing:
* Caching DNS resolvers
* DNS stub resolvers
Affected systems include both client and server systems, and any other
networked systems that include this functionality.
Overview
Deficiencies in the DNS protocol and common DNS implementations
facilitate
DNS cache poisoning attacks. Effective attack techniques against these
vulnerabilities have been demonstrated.
I. Description
DNS cache poisoning (sometimes referred to as cache pollution) is an
attack
technique that allows an attacker to introduce forged DNS
information into
the cache of a caching nameserver. The general concept has been
known for
some time, and a number of inherent deficiencies in the DNS protocol and
defects in common DNS implementations that facilitate DNS cache
poisoning
have previously been identified and described in public literature.
Examples
of these vulnerabilities can be found in Vulnerability Note VU#800113.
Recent research into these and other related vulnerabilities has
produced
extremely effective exploitation methods to achieve cache poisoning.
Tools
and techniques have been developed that can reliably poison a domain
of the
attacker's choosing on most current implementations. As a result, the
consensus of DNS software implementers is to implement source port
randomization in their resolvers as a mitigation.
US-CERT is tracking this issue as VU#800113. This reference number
corresponds to CVE-2008-1447.
II. Impact
An attacker with the ability to conduct a successful cache poisoning
attack
can cause a nameserver's clients to contact the incorrect, and possibly
malicious, hosts for particular services. Consequently, web traffic,
email,
and other important network data can be redirected to systems under the
attacker's control.
III. Solution
Apply a patch from your vendor
Patches have been released by a number of vendors to implement
source port
randomization in the nameserver. This change significantly reduces the
practicality of cache poisoning attacks. Please see the Systems Affected
section of Vulnerability Note VU#800113 for additional details for
specific
vendors.
As mentioned above, stub resolvers are also vulnerable to these attacks.
Stub resolvers that will issue queries in response to attacker
behavior, and
may receive packets from an attacker, should be patched. System
administrators should be alert for patches to client operating
systems that
implement port randomization in the stub resolver.
Workarounds
Restrict access
Administrators, particularly those who are unable to apply a patch, can
limit exposure to this vulnerability by restricting sources that can
ask for
recursion. Note that restricting access will still allow attackers with
access to authorized hosts to exploit this vulnerability.
Filter traffic at network perimeters
Because the ability to spoof IP addresses is necessary to conduct these
attacks, administrators should take care to filter spoofed addresses
at the
network perimeter. IETF Request for Comments (RFC) documents RFC
2827, RFC
3704, and RFC 3013 describe best current practices (BCPs) for
implementing
this defense. It is important to understand your network's
configuration and
service requirements before deciding what changes are appropriate.
Run a local DNS cache
In lieu of strong port randomization characteristics in a stub resolver,
administrators can protect their systems by using local caching
full-service
resolvers, both on the client systems and on servers that are
topologically
close on the network to the client systems. This should be done in
conjunction with the network segmentation and filtering strategies
mentioned
above.
Disable recursion
Disable recursion on any nameserver responding to DNS requests made by
untrusted systems.
Implement source port randomization
Vendors that implement DNS software are encouraged to review IETF
Internet
Draft, "Measures for making DNS more resilient against forged
answers," for
additional information about implementing mitigations in their products.
This document is a work in progress and may change prior to its
publication
as an RFC, if it is approved.
IV. References
* US-CERT Vulnerability Note VU#800113 -
<http://www.kb.cert.org/vuls/id/800113>
* US-CERT Vulnerability Note VU#484649 -
<http://www.kb.cert.org/vuls/id/484649>
* US-CERT Vulnerability Note VU#252735 -
<http://www.kb.cert.org/vuls/id/252735>
* US-CERT Vulnerability Note VU#927905 -
<http://www.kb.cert.org/vuls/id/927905>
* US-CERT Vulnerability Note VU#457875 -
<http://www.kb.cert.org/vuls/id/457875>
* Internet Draft: Measures for making DNS more resilient against
forged
answers -
<http://tools.ietf.org/html/draft-ietf-dnsext-forgery-resilience>
* RFC 3833 - <http://tools.ietf.org/html/rfc3833>
* RFC 2827 - <http://tools.ietf.org/html/rfc2827>
* RFC 3704 - <http://tools.ietf.org/html/rfc3704>
* RFC 3013 - <http://tools.ietf.org/html/rfc3013>
* Microsoft Security Bulletin MS08-037 -
<http://www.microsoft.com/technet/security/bulletin/ms08-037.mspx>
* Internet Systems Consortium BIND Vulnerabilities -
<http://www.isc.org/sw/bind/bind-security.php>
____________________________________________________________________
US-CERT thanks Dan Kaminsky of IOActive and Paul Vixie of Internet
Systems
Consortium (ISC) for notifying us about this problem and for helping
us to
construct this advisory.
____________________________________________________________________
The most recent version of this document can be found at:
<http://www.us-cert.gov/cas/techalerts/TA08-190B.html>
____________________________________________________________________
Feedback can be directed to US-CERT Technical Staff. Please send
email to <cert@cert.org> with "TA08-190B Feedback VU#800113" in the
subject.
____________________________________________________________________
For instructions on subscribing to or unsubscribing from this
mailing list, visit <http://www.us-cert.gov/cas/signup.html>.
____________________________________________________________________
Produced 2008 by US-CERT, a government organization.
Terms of use:
<http://www.us-cert.gov/legal.html>
____________________________________________________________________
Revision History
July 8, 2008: Initial release
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Received on Tue Jul 8 22:29:55 2008
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