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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