draft-ietf-v6ops-ra-guard-implementation-01.txt		draft-ietf-v6ops-ra-guard-implementation-02.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 March 3, 2012		Intended status: BCP March 8, 2012
	Expires: September 4, 2012		Expires: September 9, 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-01		draft-ietf-v6ops-ra-guard-implementation-02
	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 September 4, 2012.		This Internet-Draft will expire on September 9, 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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	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 identified,		such limit is hit before the upper-layer protocol is identified,
	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 first-fragment, and the necessary information is missing),
	IPv6 Source Address of the packet is a link-local address or the		the IPv6 Source Address of the packet is a link-local address or
	unspecified address (::), and the Hop Limit is 255, silently drop		the unspecified address (::), and the Hop Limit is 255, silently
	the packet.		drop the packet.
			Note: This rule should only be applied to non-fragmented IPv6
			datagrams and IPv6 fragments with a Fragment Offset of 0 (non-
			first fragments can be safely passed, since they will never
			reassemble into a complete datagram if they are part of a
			Router Advertisement received on a port where such packets are
			not allowed).
	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,		Note: For the purpose of enforcing the RA-Guard filtering policy,
	an ESP header [RFC4303] should be considered to be an "upper-layer		an ESP header [RFC4303] should be considered to be an "upper-layer
	protocol" (that is, it should be considered the last header in the		protocol" (that is, it should be considered the last header in the
	IPv6 header chain). This means that packets employing ESP would		IPv6 header chain). This means that packets employing ESP would
	be passed by the RA-Guard device to the intended destination. If		be passed by the RA-Guard device to the intended destination. If
	the destination host does not have a security association with the		the destination host does not have a security association with the
	sender of the aforementioned IPv6 packet, the packet would be		sender of the aforementioned IPv6 packet, the packet would be
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	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
	This document describes a number of techniques that have been found		This document describes a number of techniques that have been found
	to be effective to circumvent popular RA-Guard implementations.		to be effective to circumvent popular RA-Guard implementations, and
			provides advice to RA-Guard implementations such that those evasion
			vulnerabilities are eliminated.
	The most effective and efficient mitigation for these attacks would		We note that if an attacker sends a fragmented Router Advertisement
	be to prohibit the use of some IPv6 extension headers with Router		message on a port not allowed to send such packets, the first-
	Advertisement messages (as proposed by		fragment would be dropped, and the rest of the fragments would be
			passed. This means that the victim node would tie memory buffers for
			the aforementioned fragments, which would never reassemble into a
			complete datagram. If a large number of such packets were sent by an
			attacker, and the victim node failed to implement proper resource
			management for the fragment reassembly buffer, this could lead to a
			Denial of Service (DoS). However, this does not really introduce a
			new attack vector, since an attacker could always perform the same
			attack by sending forged fragmented datagram in which at least one of
			the fragments is missing. [CPNI-IPv6] discusses some resource
			management strategies that could be implemented for the fragment
			reassembly buffer.
			Finally, we note that most effective and efficient mitigation for
			these attacks would be to prohibit the use of IPv6 fragmentation with
			Router 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, Ray Hunter, Simon Perreault, Arturo		Downie, Washam Fan, David Farmer, Marc Heuse, Ray Hunter, Simon
	Servin, and Gunter van de Velde, for providing valuable comments on		Perreault, Arturo Servin, and Gunter van de Velde, for providing
	earlier versions of this document.		valuable comments on 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
	at IETF 81.		document 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
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