draft-ietf-v6ops-ra-guard-implementation-04.txt		draft-ietf-v6ops-ra-guard-implementation-05.txt
	IPv6 Operations Working Group (v6ops) F. Gont		IPv6 Operations Working Group (v6ops) F. Gont
	Internet-Draft UK CPNI		Internet-Draft UK CPNI
	Updates: 6105 (if approved) May 22, 2012		Updates: 6105 (if approved) October 26, 2012
	Intended status: BCP		Intended status: BCP
	Expires: November 23, 2012		Expires: April 29, 2013
	Implementation Advice for IPv6 Router Advertisement Guard (RA-Guard)		Implementation Advice for IPv6 Router Advertisement Guard (RA-Guard)
	draft-ietf-v6ops-ra-guard-implementation-04		draft-ietf-v6ops-ra-guard-implementation-05
	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 November 23, 2012.		This Internet-Draft will expire on April 29, 2013.
	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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	present in the first fragment (rather than the second).		present in the first fragment (rather than the second).
	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. If the IPv6 Source Address of the packet is not a link-local		1. If the IPv6 Source Address of the packet is not a link-local
	address (fe80::/10), pass the packet.		address (fe80::/10), RA-Guard MUST pass the packet.
	Section 6.1.2 of [RFC4861] requires nodes to discard Router		RATIONALE: Section 6.1.2 of [RFC4861] requires nodes to
	Advertisement messages if their IPv6 Source Address is not a		discard Router Advertisement messages if their IPv6 Source
	link-local address.		Address is not a link-local address.
	2. If the Hop Limit is not 255, pass the packet.		2. If the Hop Limit is not 255, RA-Guard MUST pass the packet.
	Section 6.1.2 of [RFC4861] requires nodes to discard Router		RATIONALE: Section 6.1.2 of [RFC4861] requires nodes to
	Advertisement messages if their Hop Limit is not 255.		discard Router Advertisement messages if their Hop Limit is
			not 255.
	3. Try to identify whether the packet is an ICMPv6 Router		3. RA-Guard MUST parse the IPv6 entire header chain present in the
	Advertisement message, by parsing the IPv6 header chain. When		packet, to identify whether the packet is a Router Advertisement
	doing so, enforce a limit on the maximum number of Extension		message.
	Headers that is allowed for each packet, and if such limit is hit
	before the upper-layer protocol is identified, drop the packet.
	[RFC6564] specifies a uniform format for IPv6 Extension		RATIONALE: [RFC6564] specifies a uniform format for IPv6
	Header, thus meaning that an IPv6 node should be able to parse		Extension Header, thus meaning that an IPv6 node can parse an
	an IPv6 header chain even if it contains Extension Headers		IPv6 header chain even if it contains Extension Headers that
	that are not currently supported by that node.		are not currently supported by that node. Additionally,
			[I-D.ietf-6man-oversized-header-chain] requires that if a
			packet is fragmented, the first fragment contains the entire
			IPv6 header chain.
	4. If the layer-2 device is unable to identify whether the packet is		RA-Guard implementations MUST NOT enforce a limit on the
	an ICMPv6 Router Advertisement message or not (i.e., the packet		number of bytes they can inspect (starting from the beginning
	is a first-fragment, and the necessary information is missing),		of the IPv6 packet), since this could introduce false-
	drop the packet.		positives: legitimate packets could be dropped simply because
			the RA-Guard device does not parse the entire IPv6 header
			chain present in the packet. An implementation that has such
			an implementation-specific limit MUST NOT claim compliance
			with this specification, and MUST pass the packet when such
			implementation-specific limit is reached.
	Note: This rule should only be applied to non-fragmented IPv6		4. When parsing the IPv6 header chain, if the packet is a first-
	datagrams and IPv6 fragments with a Fragment Offset of 0 (non-		fragment (i.e., a packet containing a Fragment Header with the
	first fragments can be safely passed, since they will never		Fragment Offset set to 0) and it fails to contain the entire IPv6
	reassemble into a complete datagram if they are part of a		header chain (i.e., all the headers starting from the IPv6 header
	Router Advertisement received on a port where such packets are		up to, and including, the upper-layer header), RA-Guard MUST drop
	not allowed).		the packet, and SHOULD log the packet drop event in an
			implementation-specific manner as a security fault.
	5. If the packet is identified to be an ICMPv6 Router Advertisement		RATIONALE: [I-D.ietf-6man-oversized-header-chain] specifies
	message, drop the packet.		that the first-fragment (i.e., the fragment with the Fragment
			Offset set to 0) MUST contain the entire IPv6 header chain,
			and allows intermmediate systems such as routers to drop those
			packets that fail to comply with this requirement.
	6. In all other cases, pass the packet as usual.		NOTE: This rule should only be applied to 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).
	Note: For the purpose of enforcing the RA-Guard filtering policy,		5. When parsing the IPv6 header chain, if the packet is identified
			to be an ICMPv6 Router Advertisement message, RA-Guard MUST drop
			the packet, and SHOULD log the packet drop event in an
			implementation-specific manner as a security fault.
			RATIONALE: By definition, Router Advertisement messages MUST
			originate on-link, MUST have a link-local IPv6 Source Address,
			and MUST have a Hop Limit value of 255. [RFC4861].
			6. In all other cases, RA-Guard MUST 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		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
	dropped. Otherwise, if the packet is considered valid by the		dropped. Otherwise, if the packet is considered valid by the
	IPsec implementation at the receiving host and encapsulates a		IPsec implementation at the receiving host and encapsulates a
	Router Advertisement message, it is up to the receiving host what		Router Advertisement message, it is up to the receiving host what
	to do with such packet.		to do with such packet.
	If a packet is dropped due to this filtering policy, then the packet		If a packet is dropped due to this filtering policy, then the packet
	drop event SHOULD be logged. The logging mechanism SHOULD include a		drop event SHOULD be logged in an implementation-specific manner as a
	drop counter dedicated to RA-Guard packet drops.		security fault. The logging mechanism SHOULD include a drop counter
			dedicated to RA-Guard packet drops.
	In order to protect current end-node IPv6 implementations, Rule #4		In order to protect current end-node IPv6 implementations, Rule #4
	has been defined as a default rule to drop packets that cannot be		has been defined as a default rule to drop packets that cannot be
	positively identified as not being Router Advertisement (RA) messages		positively identified as not being Router Advertisement (RA) messages
	(possibly because the packet contains fragments that do not contain		(because the packet is a fragment that fails to include the entire
	the entire IPv6 header chain). This means that, at least in theory,		IPv6 header chain). This means that, at least in theory, RA-Guard
	RA-Guard could result in false-positive blocking of some legitimate		could result in false-positive blocking of some legitimate non-RA
	non-RA packets that could not be positively identified as being		packets that could not be positively identified as being non-RA. In
	non-RA. In order to reduce the likelihood of false positives, Rule		order to reduce the likelihood of false positives, Rule #1 and Rule
	#1 and Rule #2 require that packets that would not pass the required		#2 require that packets that would not pass the required validation
	validation checks for RA messages (Section 6.1.2 of [RFC4861]) be		checks for RA messages (Section 6.1.2 of [RFC4861]) be passed without
	passed without further inspection. In any case, as noted in		further inspection. In any case, as noted in
	[I-D.gont-6man-oversized-header-chain], IPv6 packets that fail to		[I-D.ietf-6man-oversized-header-chain], IPv6 packets that fail to
	include the entire IPv6 header chain are anyway unlikely to survive		include the entire IPv6 header chain are virtually impossible to
	in real networks. Whilst currently legitimate from a specifications		police with state-less filters and firewalls, and hence are unlikely
	standpoint, they are virtually impossible to police with state-less		to survive in real networks. [I-D.ietf-6man-oversized-header-chain]
	filters and firewalls, and are hence likely to be blocked by such		requires that hosts employing fragmentation include the entire IPv6
	filters and firewalls.		header chain in the first fragment (the fragment with the Fragment
			Offset set to 0), thus eliminating the aforementioned false
			positives.
	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.
	The aforementioned filtering rules implicitly handle the case of		The aforementioned filtering rules implicitly handle the case of
	fragmented packets: if the RA-Guard device fails to identify the		fragmented packets: if the RA-Guard device fails to identify the
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	Denial of Service (DoS). However, this does not really introduce a		Denial of Service (DoS). However, this does not really introduce a
	new attack vector, since an attacker could always perform the same		new attack vector, since an attacker could always perform the same
	attack by sending forged fragmented datagram in which at least one of		attack by sending forged fragmented datagram in which at least one of
	the fragments is missing. [CPNI-IPv6] discusses some resource		the fragments is missing. [CPNI-IPv6] discusses some resource
	management strategies that could be implemented for the fragment		management strategies that could be implemented for the fragment
	reassembly buffer.		reassembly buffer.
	We note that most effective and efficient mitigation for these		We note that most effective and efficient mitigation for these
	attacks would be to prohibit the use of IPv6 fragmentation with		attacks would be to prohibit the use of IPv6 fragmentation with
	Router Advertisement messages (as proposed by		Router Advertisement messages (as proposed by
	[I-D.gont-6man-nd-extension-headers]), such that the RA-Guard		[I-D.ietf-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.
	Finally, we note that RA-Guard only mitigates attack vectors based on		Finally, we note that RA-Guard only mitigates attack vectors based on
	ICMPv6 Router advertisement messages. Protection against similar		ICMPv6 Router advertisement messages. Protection against similar
	attacks based on other messages (such as DCHPv6) is considered out of		attacks based on other messages (such as DCHPv6) is considered out of
	the scope of this document, and left for other documents(e.g.		the scope of this document, and left for other documents(e.g.
	[DHCPv6-Shield]).		[DHCPv6-Shield]).
	7. Acknowledgements		7. Acknowledgements
			The author would like to thank Ran Atkinson, who provided very
			detailed comments and suggested text that was incorporated into this
			document.
	The author would like to thank Ran Atkinson, Karl Auer, Robert		The author would like to thank Ran Atkinson, Karl Auer, Robert
	Downie, Washam Fan, David Farmer, Marc Heuse, Nick Hilliard, Ray		Downie, Washam Fan, David Farmer, Marc Heuse, Nick Hilliard, Ray
	Hunter, Joel Jaeggli, Simon Perreault, Arturo Servin, Gunter van de		Hunter, Joel Jaeggli, Simon Perreault, Arturo Servin, Gunter van de
	Velde, James Woodyatt, and Bjoern A. Zeeb, for providing valuable		Velde, James Woodyatt, and Bjoern A. Zeeb, for providing valuable
	comments on earlier versions of this document.		comments on earlier versions of this document.
	The author would like to thank Arturo Servin, who presented this		The author would like to thank Arturo Servin, who presented this
	document 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
	skipping to change at page 15, line 26		skipping to change at page 15, line 26
	"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,		"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
	September 2007.		September 2007.
	[RFC5722] Krishnan, S., "Handling of Overlapping IPv6 Fragments",		[RFC5722] Krishnan, S., "Handling of Overlapping IPv6 Fragments",
	RFC 5722, December 2009.		RFC 5722, December 2009.
	[RFC6564] Krishnan, S., Woodyatt, J., Kline, E., Hoagland, J., and		[RFC6564] Krishnan, S., Woodyatt, J., Kline, E., Hoagland, J., and
	M. Bhatia, "A Uniform Format for IPv6 Extension Headers",		M. Bhatia, "A Uniform Format for IPv6 Extension Headers",
	RFC 6564, April 2012.		RFC 6564, April 2012.
			[I-D.ietf-6man-oversized-header-chain]
			Gont, F. and V. Manral, "Security and Interoperability
			Implications of Oversized IPv6 Header Chains",
			draft-ietf-6man-oversized-header-chain-01 (work in
			progress), July 2012.
			[I-D.ietf-6man-nd-extension-headers]
			Gont, F., "Security Implications of the Use of IPv6
			Extension Headers with IPv6 Neighbor Discovery",
			draft-ietf-6man-nd-extension-headers-00 (work in
			progress), June 2012.
	8.2. Informative References		8.2. 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-01 (work in
	progress), April 2012.
	[I-D.gont-6man-nd-extension-headers]
	Gont, F., "Security Implications of the Use of IPv6
	Extension Headers with IPv6 Neighbor Discovery",
	draft-gont-6man-nd-extension-headers-02 (work in
	progress), January 2012.
	[DHCPv6-Shield]		[DHCPv6-Shield]
	Gont, F., "DHCPv6-Shield: Protecting Against Rogue DHCPv6		Gont, F., "DHCPv6-Shield: Protecting Against Rogue DHCPv6
	Servers", IETF Internet Draft,		Servers", IETF Internet Draft,
	draft-gont-opsec-dhcpv6-shield, work in progress,		draft-gont-opsec-dhcpv6-shield, work in progress,
	May 2012.		May 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).
	skipping to change at page 16, line 24		skipping to change at page 16, line 24
	kame/rafixd/>.		kame/rafixd/>.
	[ramond] "ramond", <http://ramond.sourceforge.net/>.		[ramond] "ramond", <http://ramond.sourceforge.net/>.
	[SI6-FRAG]		[SI6-FRAG]
	SI6 Networks, "IPv6 NIDS evasion and improvements in IPv6		SI6 Networks, "IPv6 NIDS evasion and improvements in IPv6
	fragmentation/reassembly", 2012, <http://		fragmentation/reassembly", 2012, <http://
	blog.si6networks.com/2012/02/		blog.si6networks.com/2012/02/
	ipv6-nids-evasion-and-improvements-in.html>.		ipv6-nids-evasion-and-improvements-in.html>.
			[SI6-IPv6]
			"SI6 Networks' IPv6 toolkit",
			<http://www.si6networks.com/tools/ipv6toolkit>.
	[THC-IPV6]		[THC-IPV6]
	"The Hacker's Choice IPv6 Attack Toolkit",		"The Hacker's Choice IPv6 Attack Toolkit",
	<http://www.thc.org/thc-ipv6/>.		<http://www.thc.org/thc-ipv6/>.
	Appendix A. Assessment tools		Appendix A. Assessment tools
	CPNI has produced assessment tools (which have not yet been made		[SI6-IPv6] is a publicly-available set of tools (for Linux, *BSD, and
	publicly available) to assess RA-Guard implementations with respect		Mac OS) that implements the techniques described in this document.
	to the issues described in this document. If you think that you
	would benefit from these tools, we might be able to provide a copy of
	the tools (please contact Fernando Gont at fernando@gont.com.ar).
	[THC-IPV6] is a publicly-available set of tools that implements some		[THC-IPV6] is a publicly-available set of tools (for Linux) that
	of the techniques described in this document.		implements some of the techniques described in this document.
	Appendix B. Advice and guidance to vendors		Appendix B. Advice and guidance to vendors
	Vendors are urged to contact CSIRTUK (csirt@cpni.gsi.gov.uk) if they		Vendors are urged to contact CSIRTUK (csirt@cpni.gsi.gov.uk) if they
	think they may be affected by the issues described in this document.		think they may be affected by the issues described in this document.
	As the lead coordination centre for these issues, CPNI is well placed		As the lead coordination centre for these issues, CPNI is well placed
	to give advice and guidance as required.		to give advice and guidance as required.
	CPNI works extensively with government departments and agencies,		CPNI works extensively with government departments and agencies,
	commercial organisations and the academic community to research		commercial organisations and the academic community to research
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