draft-ietf-v6ops-ra-guard-implementation-00.txt   draft-ietf-v6ops-ra-guard-implementation-01.txt 
IPv6 Operations Working Group (v6ops) F. Gont IPv6 Operations Working Group (v6ops) F. Gont
Internet-Draft UK CPNI Internet-Draft UK CPNI
Intended status: BCP February 12, 2012 Intended status: BCP March 3, 2012
Expires: August 15, 2012 Expires: September 4, 2012
Implementation Advice for IPv6 Router Advertisement Guard (RA-Guard) Implementation Advice for IPv6 Router Advertisement Guard (RA-Guard)
draft-ietf-v6ops-ra-guard-implementation-00 draft-ietf-v6ops-ra-guard-implementation-01
Abstract Abstract
The IPv6 Router Advertisement Guard (RA-Guard) mechanism is commonly The IPv6 Router Advertisement Guard (RA-Guard) mechanism is commonly
employed to mitigate attack vectors based on forged ICMPv6 Router employed to mitigate attack vectors based on forged ICMPv6 Router
Advertisement messages. Many existing IPv6 deployments rely on RA- Advertisement messages. Many existing IPv6 deployments rely on RA-
Guard as the first line of defense against the aforementioned attack Guard as the first line of defense against the aforementioned attack
vectors. However, some implementations of RA-Guard have been found vectors. However, some implementations of RA-Guard have been found
to be prone to circumvention by employing IPv6 Extension Headers. to be prone to circumvention by employing IPv6 Extension Headers.
This document describes the evasion techniques that affect the This document describes the evasion techniques that affect the
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 15, 2012. This Internet-Draft will expire on September 4, 2012.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Evasion techniques for some Router Advertisement Guard (RA 2. Evasion techniques for some Router Advertisement Guard (RA
Guard) implementations . . . . . . . . . . . . . . . . . . . . 4 Guard) implementations . . . . . . . . . . . . . . . . . . . . 4
2.1. Attack Vector based on IPv6 Extension Headers . . . . . . 4 2.1. Attack Vector based on IPv6 Extension Headers . . . . . . 4
2.2. Attack vector based on IPv6 fragmentation . . . . . . . . 4 2.2. Attack vector based on IPv6 fragmentation . . . . . . . . 4
3. RA-Guard implementation advice . . . . . . . . . . . . . . . . 8 3. RA-Guard implementation advice . . . . . . . . . . . . . . . . 8
4. Other Implications . . . . . . . . . . . . . . . . . . . . . . 9 4. Other Implications . . . . . . . . . . . . . . . . . . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10 5. Security Considerations . . . . . . . . . . . . . . . . . . . 11
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7.1. Normative References . . . . . . . . . . . . . . . . . . . 12 7.1. Normative References . . . . . . . . . . . . . . . . . . . 13
7.2. Informative References . . . . . . . . . . . . . . . . . . 12 7.2. Informative References . . . . . . . . . . . . . . . . . . 13
Appendix A. Changes from previous versions of the draft (to Appendix A. Changes from previous versions of the draft (to
be removed by the RFC Editor before publication be removed by the RFC Editor before publication
of this document as a RFC . . . . . . . . . . . . . . 13 of this document as a RFC . . . . . . . . . . . . . . 15
A.1. Changes from A.1. Changes from
draft-gont-v6ops-ra-guard-implementation-01 . . . . . . . 13 draft-ietf-v6ops-ra-guard-implementation-00 . . . . . . . 15
A.2. Changes from A.2. Changes from
draft-gont-v6ops-ra-guard-implementation-00 . . . . . . . 13 draft-gont-v6ops-ra-guard-implementation-01 . . . . . . . 15
A.3. Changes from draft-gont-v6ops-ra-guard-evasion-01 . . . . 13 A.3. Changes from
Appendix B. Assessment tools . . . . . . . . . . . . . . . . . . 14 draft-gont-v6ops-ra-guard-implementation-00 . . . . . . . 15
Appendix C. Advice and guidance to vendors . . . . . . . . . . . 15 A.4. Changes from draft-gont-v6ops-ra-guard-evasion-01 . . . . 15
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 16 Appendix B. Assessment tools . . . . . . . . . . . . . . . . . . 16
Appendix C. Advice and guidance to vendors . . . . . . . . . . . 17
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 18
1. Introduction 1. Introduction
IPv6 Router Advertisement Guard (RA-Guard) is a mitigation technique IPv6 Router Advertisement Guard (RA-Guard) is a mitigation technique
for attack vectors based on ICMPv6 Router Advertisement messages. for attack vectors based on ICMPv6 Router Advertisement messages.
[RFC6104] describes the problem statement of "Rogue IPv6 Router [RFC6104] describes the problem statement of "Rogue IPv6 Router
Advertisements", and [RFC6105] specifies the "IPv6 Router Advertisements", and [RFC6105] specifies the "IPv6 Router
Advertisement Guard" functionality. Advertisement Guard" functionality.
The basic concept behind RA-Guard is that a layer-2 device filters The basic concept behind RA-Guard is that a layer-2 device filters
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3. RA-Guard implementation advice 3. RA-Guard implementation advice
The following filtering rules MUST be implemented as part of an "RA- The following filtering rules MUST be implemented as part of an "RA-
Guard" implementation on those ports that are not allowed to send Guard" implementation on those ports that are not allowed to send
ICMPv6 Router Advertisement messages, such that the vulnerabilities ICMPv6 Router Advertisement messages, such that the vulnerabilities
discussed in this document are eliminated: discussed in this document are eliminated:
1. When trying to identify an ICMPv6 Router Advertisement message, 1. When trying to identify an ICMPv6 Router Advertisement message,
follow the IPv6 header chain, enforcing a limit on the maximum follow the IPv6 header chain, enforcing a limit on the maximum
number of Extension Headers that is allowed for each packet. If number of Extension Headers that is allowed for each packet. If
such limit is hit before the upper-layer protocol is can be such limit is hit before the upper-layer protocol is identified,
determined, silently drop the packet. silently drop the packet.
2. If the packet is identified to be an ICMPv6 Router Advertisement 2. If the packet is identified to be an ICMPv6 Router Advertisement
message, silently drop the packet. message, silently drop the packet.
3. If the layer-2 device is unable to identify whether the packet is 3. If the layer-2 device is unable to identify whether the packet is
an ICMPv6 Router Advertisement message or not (i.e., the packet an ICMPv6 Router Advertisement message or not (i.e., the packet
is a fragment, and the necessary information is missing), the is a fragment, and the necessary information is missing), the
IPv6 Source Address of the packet is a link-local address or the IPv6 Source Address of the packet is a link-local address or the
unspecified address (::), and the Hop Limit is 255, silently drop unspecified address (::), and the Hop Limit is 255, silently drop
the packet. the packet.
4. In all other cases, pass the packet as usual. 4. In all other cases, pass the packet as usual.
Note: For the purpose of enforcing the RA-Guard filtering policy,
an ESP header [RFC4303] should be considered to be an "upper-layer
protocol" (that is, it should be considered the last header in the
IPv6 header chain). This means that packets employing ESP would
be passed by the RA-Guard device to the intended destination. If
the destination host does not have a security association with the
sender of the aforementioned IPv6 packet, the packet would be
dropped. Otherwise, if the packet is considered valid by the
IPsec implementation at the receiving host and encapsulates a
Router Advertisement message, it is up to the receiving host what
to do with such packet.
In order to protect current end-node IPv6 implementations, Rule #3
has been defined as a default rule to drop packets that cannot be
positively identified as RA packets or not (perhaps due to the fact
that it contains fragments that do not contain the entire IPv6 header
chain). This means that, at least in theory, RA-Guard could result
in false-positive blocking of some legitimate non-RA packets that
could not be positively identified as being non-RA. In order to
reduce the likelihood of false positives, Rule #3 also requires that
an RA-Guard implementation check, before dropping an unidentifiable
packet, that it has an IPv6 Source Address that is a link-local
address or the unspecified address (::), and that the Hop Limit is
255. In any case, as noted in
[I-D.gont-6man-oversized-header-chain], IPv6 packets that fail to
include the entire IPv6 header chain are anyway unlikely to survive
in real networks. Whilst currently legitimate from a specifications
standpoint, they are virtually impossible to police with state-less
filters and firewalls, and are hence likely to be blocked by such
filters and firewalls.
This filtering policy assumes that host implementations require that This filtering policy assumes that host implementations require that
the IPv6 Source Address of ICMPv6 Router Advertisement messages be a the IPv6 Source Address of ICMPv6 Router Advertisement messages be a
link-local address, and that they discard the packet if this check link-local address, and that they discard the packet if this check
fails, as required by the current IETF specifications [RFC4861]. fails, as required by the current IETF specifications [RFC4861].
Additionally, it assumes that hosts require the Hop Limit of Neighbor Additionally, it assumes that hosts require the Hop Limit of Neighbor
Discovery messages to be 255, and discard those packets otherwise. Discovery messages to be 255, and discard those packets otherwise.
Note that the aforementioned filtering rules implicitly handle the Finally, note that the aforementioned filtering rules implicitly
case of fragmented packets: if the RA-Guard device fails to identify handle the case of fragmented packets: if the RA-Guard device fails
the upper-layer protocol as a result of the use of fragmentation, the to identify the upper-layer protocol as a result of the use of
corresponding packets would be silently dropped. fragmentation, the corresponding packets would be silently dropped.
4. Other Implications 4. Other Implications
A similar concept to that of "RA-Guard" has been implemented for A similar concept to that of "RA-Guard" has been implemented for
protecting against forged DHCPv6 messages. Such protection can be protecting against forged DHCPv6 messages. Such protection can be
circumvented with the same techniques discussed in this document, and circumvented with the same techniques discussed in this document, and
the counter-measures for such evasion attack are analogous to those the counter-measures for such evasion attack are analogous to those
described in Section 3 of this document. described in Section 3 of this document.
5. Security Considerations 5. Security Considerations
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be to prohibit the use of some IPv6 extension headers with Router be to prohibit the use of some IPv6 extension headers with Router
Advertisement messages (as proposed by Advertisement messages (as proposed by
[I-D.gont-6man-nd-extension-headers]), such that the RA-Guard [I-D.gont-6man-nd-extension-headers]), such that the RA-Guard
functionality is easier to implement. However, since such mitigation functionality is easier to implement. However, since such mitigation
would require an update to existing implementations, it cannot be would require an update to existing implementations, it cannot be
relied upon in the short or near term. relied upon in the short or near term.
6. Acknowledgements 6. Acknowledgements
The author would like to thank Ran Atkinson, Karl Auer, Robert The author would like to thank Ran Atkinson, Karl Auer, Robert
Downie, David Farmer, Marc Heuse, Simon Perreault, Arturo Servin, and Downie, David Farmer, Marc Heuse, Ray Hunter, Simon Perreault, Arturo
Gunter van de Velde, for providing valuable comments on earlier Servin, and Gunter van de Velde, for providing valuable comments on
versions of this document. earlier versions of this document.
The author would like to thank Arturo Servin, who presented this work The author would like to thank Arturo Servin, who presented this work
at IETF 81. at IETF 81.
This document resulted from the project "Security Assessment of the This document resulted from the project "Security Assessment of the
Internet Protocol version 6 (IPv6)" [CPNI-IPv6], carried out by Internet Protocol version 6 (IPv6)" [CPNI-IPv6], carried out by
Fernando Gont on behalf of the UK Centre for the Protection of Fernando Gont on behalf of the UK Centre for the Protection of
National Infrastructure (CPNI). The author would like to thank the National Infrastructure (CPNI). The author would like to thank the
UK CPNI, for their continued support. UK CPNI, for their continued support.
7. References 7. References
7.1. Normative References 7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, December 2005.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007. September 2007.
7.2. Informative References 7.2. Informative References
[RFC6104] Chown, T. and S. Venaas, "Rogue IPv6 Router Advertisement [RFC6104] Chown, T. and S. Venaas, "Rogue IPv6 Router Advertisement
Problem Statement", RFC 6104, February 2011. Problem Statement", RFC 6104, February 2011.
[RFC6105] Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and J. [RFC6105] Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and J.
Mohacsi, "IPv6 Router Advertisement Guard", RFC 6105, Mohacsi, "IPv6 Router Advertisement Guard", RFC 6105,
February 2011. February 2011.
[I-D.gont-6man-oversized-header-chain]
Gont, F. and V. Manral, "Security and Interoperability
Implications of Oversized IPv6 Header Chains",
draft-gont-6man-oversized-header-chain-00 (work in
progress), February 2012.
[I-D.gont-6man-nd-extension-headers] [I-D.gont-6man-nd-extension-headers]
Gont, F., "Security Implications of the Use of IPv6 Gont, F., "Security Implications of the Use of IPv6
Extension Headers with IPv6 Neighbor Discovery", Extension Headers with IPv6 Neighbor Discovery",
draft-gont-6man-nd-extension-headers-02 (work in draft-gont-6man-nd-extension-headers-02 (work in
progress), January 2012. progress), January 2012.
[CPNI-IPv6] [CPNI-IPv6]
Gont, F., "Security Assessment of the Internet Protocol Gont, F., "Security Assessment of the Internet Protocol
version 6 (IPv6)", UK Centre for the Protection of version 6 (IPv6)", UK Centre for the Protection of
National Infrastructure, (available on request). National Infrastructure, (available on request).
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[ramond] "ramond", <http://ramond.sourceforge.net/>. [ramond] "ramond", <http://ramond.sourceforge.net/>.
[THC-IPV6] [THC-IPV6]
"THC-IPV6", <http://www.thc.org/thc-ipv6/>. "THC-IPV6", <http://www.thc.org/thc-ipv6/>.
Appendix A. Changes from previous versions of the draft (to be removed Appendix A. Changes from previous versions of the draft (to be removed
by the RFC Editor before publication of this document as a by the RFC Editor before publication of this document as a
RFC RFC
A.1. Changes from draft-gont-v6ops-ra-guard-implementation-01 A.1. Changes from draft-ietf-v6ops-ra-guard-implementation-00
o The filtering rules in Section 3 have been further clarified.
A.2. Changes from draft-gont-v6ops-ra-guard-implementation-01
o Document resubmitted as draft-ietf to reflect wg adoption. o Document resubmitted as draft-ietf to reflect wg adoption.
A.2. Changes from draft-gont-v6ops-ra-guard-implementation-00 A.3. Changes from draft-gont-v6ops-ra-guard-implementation-00
o Miscellaneous (minor) editorial changes. o Miscellaneous (minor) editorial changes.
o The filtering rules in Section 3 have been polished. o The filtering rules in Section 3 have been polished.
A.3. Changes from draft-gont-v6ops-ra-guard-evasion-01 A.4. Changes from draft-gont-v6ops-ra-guard-evasion-01
o The contents were updated to reflect that the evasion o The contents were updated to reflect that the evasion
vulnerabilities are based on implementation flaws, rather than on vulnerabilities are based on implementation flaws, rather than on
the RA-Guard "concept" itself. the RA-Guard "concept" itself.
o The I-D now focuses on providing advice to RA-Guard implementers. o The I-D now focuses on providing advice to RA-Guard implementers.
Appendix B. Assessment tools Appendix B. Assessment tools
CPNI has produced assessment tools (which have not yet been made CPNI has produced assessment tools (which have not yet been made
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