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IPv6 maintenance Working Group (6man)                            F. Gont
Internet-Draft                                    SI6 Networks / UTN-FRH
Updates: 2460, 4443 (if approved)                                 W. Liu
Intended status: Standards Track                     Huawei Technologies
Expires: September 22, 2013                               March 21, 2013


         Security Implications of IPv6 Options of Type 10xxxxxx
                draft-gont-6man-ipv6-smurf-amplifier-03

Abstract

   When an IPv6 node processing an IPv6 packet does not support an IPv6
   option whose two-highest-order bits of the Option Type are '10', it
   is required to respond with an ICMPv6 Parameter Problem error
   message, even if the Destination Address of the packet was a
   multicast address.  This feature provides an amplification vector,
   opening the door to an IPv6 version of the 'Smurf' Denial-of-Service
   (DoS) attack found in IPv4 networks.  This document discusses the
   security implications of the aforementioned options, and formally
   updates RFC 2460 and RFC 4443 such that this attack vector is
   eliminated.  Additionally, it describes a number of operational
   mitigations that could be deployed against this attack vector.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.  This document may not be modified,
   and derivative works of it may not be created, and it may not be
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   This Internet-Draft will expire on September 22, 2013.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Updating RFC 2460 and RFC 4443 . . . . . . . . . . . . . . . .  5
   3.  Operational mitigations  . . . . . . . . . . . . . . . . . . .  7
   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  8
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 11
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12




























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1.  Introduction

   IPv6 has eliminated most of the amplification vectors that were
   available in IPv4 to perform 'Smurf'-like Denial of Service (DoS)
   attacks [CERT1998].  However, an amplification vector has been left
   in the core IPv6 and ICMPv6 specifications ([RFC2460] and [RFC4443])
   that would allow for an IPv6 version of the 'Smurf' Denial-of-Service
   (DoS) attacks [CERT1998] [RFC6274] found in IPv4 networks.  The
   aforementioned vector is based on the use of unsupported IPv6
   options, used in combination with multicast destinations.

   [RFC2460] specifies, in Section 4.2, that when a node processing an
   IPv6 packet does not support an IPv6 option whose two-highest-order
   bits of the Option Type are '10', it should respond with an ICMPv6
   Parameter Problem error message, even if the Destination Address of
   the packet was a multicast address.  [RFC4443] specifies, in Section
   2.4 (page 6), that packets destined to an IPv6 multicast address
   should not elicit ICMPv6 error messages, with the exception of ICMPv6
   Packet Too Big messages (such that Path-MTU Discovery works for IPv6
   multicast) and the Parameter Problem Message, Code 2 for reporting an
   unrecognized IPv6 option that has the Option Type highest-order two
   bits set to 10.

   This feature provides an amplification vector, opening the door to an
   IPv6 version of the 'Smurf' Denial-of-Service (DoS) attack [CERT1998]
   [RFC6274] found in IPv4 networks.

   An attacker could exploit the aforementioned amplification vector by
   sending forged IPv6 packets with the IPv6 address of the victim
   system as the Source Address of his packets, a multicast address as
   the Destination Address, and an unsupported option (with an Option
   Type of '10xxxxxx') in a Destination Options Header.  Upon receipt of
   the forged packet, each receiving host would respond with an ICMPv6
   Parameter Problem, code 2, error message, pointing to the unsupported
   option type.  Thus, the systems belonging to the multicast group
   specified by the multicast address contained in the Destination
   Address field would serve as an 'amplifier network'.

      It should be noted that if the multicast RPF check is used (e.g.
      to prevent routing loops), this would prevent an attacker from
      forging the Source Address of a packet to an arbitrary value, thus
      preventing an attacker from launching this attack against a remote
      network.

      Chapter 5 of [Juniper2010] discusses multicast RPF configuration
      for Juniper routers.

   Section 2 updates RFC 2460 [RFC2460] and RFC 4443 [RFC4443], such



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   that the aforementioned attack vector is eliminated.  Section 3
   describes a number of operational mitigations for the aforementioned
   attack vector.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].












































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2.  Updating RFC 2460 and RFC 4443

   Considering the security implications discussed in Section 1, and
   since there are no known legitimate uses of IPv6 options of type
   '10xxxxxx', this document updates the corresponding specifications to
   eliminate these issues.

   The following text in Section 4.2 (page 9) of [RFC2460]:

      10 - discard the packet and, regardless of whether or not the
           packet's Destination Address was a multicast address, send an
           ICMP Parameter Problem, Code 2, message to the packet's
           Source Address, pointing to the unrecognized Option Type.

   is replaced with:

    10 - discard the packet and send an ICMP Parameter Problem, Code 2,
         message to the packet's Source Address (pointing to the
         unrecognized Option Type), only if (1) the packet's Destination
         Address was not a multicast address, or (2) the packet's
         Destination Address was a multicast address, but the node
         sending the Parameter Problem error message can assert that
         the Source Address of the packet eliciting the error message
         has not been forged.

   Additionally, the following text in Section 2.4 (page 6) of
   [RFC4443]:

       (e.3) A packet destined to an IPv6 multicast address.  (There are
             two exceptions to this rule: (1) the Packet Too Big Message
             (Section 3.2) to allow Path MTU discovery to work for IPv6
             multicast, and (2) the Parameter Problem Message, Code 2
             (Section 3.4) reporting an unrecognized IPv6 option (see
             Section 4.2 of [IPv6]) that has the Option Type highest-
             order two bits set to 10).

   is replaced with:














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      (e.3) A packet destined to an IPv6 multicast address.  (There is
            one exception to this rule: the Packet Too Big Message
            (Section 3.2) to allow Path MTU discovery to work for IPv6
            multicast).

      (e.3) A packet destined to an IPv6 multicast address.  (There are
            two exceptions to this rule: (1) the Packet Too Big Message
            (Section 3.2) to allow Path MTU discovery to work for IPv6
            multicast, and (2) the Parameter Problem Message, Code 2
            (Section 3.4) reporting an unrecognized IPv6 option that has
            the Option Type highest-order two bits set to 10, *provided*
            the node sending the Parameter Problem message can assert
            that the Source Address of the packet eliciting the error
            message has not been forged.).





































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3.  Operational mitigations

   This section describes a number of operational mitigations that could
   be implemented for the aforementioned attack vector:

   o  Firstly, IPv6 nodes should limit their ICMPv6 traffic.  This is a
      general mitigation technique for any bandwidth-exhaustion attack
      that relies on ICMPv6 traffic.  This could be enforced at the
      hosts themselves, or at any router connecting such hosts to the
      public network.

   o  Secondly, as noted in Section 1 of this document, the multicast
      RPF check could be enabled such that an attacker cannot forge the
      Source Address of a packet to an arbitrary value, thus preventing
      an attacker from launching this attack against a remote network.




































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4.  IANA Considerations

   There are no IANA registries within this document.  The RFC-Editor
   can remove this section before publication of this document as an
   RFC.














































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5.  Security Considerations

   This document describes how IPv6 options whose two-highest-order bits
   of the Option Type are '10' could be exploited to perform an IPv6
   version of the 'Smurf' Denial-of-Service (DoS) attack [CERT1998]
   [RFC6274] found in IPv4 networks.  It formally updates RFC 2460
   [RFC2460] such that this attack vector is eliminated, and also
   describes a number of operational mitigations that could be deployed
   against this attack vector.










































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6.  Acknowledgements

   The authors would like to thank (in alphabetical order) Francis
   Dupont, Joel Halpern, Suresh Krishnan, Simon Perreault, Dave Thaler,
   and Ole Troan, for providing valuable comments on earlier versions of
   this document.

   This document is based on the technical report "Security Assessment
   of the Internet Protocol version 6 (IPv6)" [CPNI-IPv6] authored by
   Fernando Gont on behalf of the UK Centre for the Protection of
   National Infrastructure (CPNI).

   Fernando Gont would like to thank CPNI (http://www.cpni.gov.uk) for
   their continued support.





































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7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

   [RFC4443]  Conta, A., Deering, S., and M. Gupta, "Internet Control
              Message Protocol (ICMPv6) for the Internet Protocol
              Version 6 (IPv6) Specification", RFC 4443, March 2006.

7.2.  Informative References

   [RFC6274]  Gont, F., "Security Assessment of the Internet Protocol
              Version 4", RFC 6274, July 2011.

   [CPNI-IPv6]
              Gont, F., "Security Assessment of the Internet Protocol
              version 6 (IPv6)",  UK Centre for the Protection of
              National Infrastructure, (available on request).

   [CERT1998]
              CERT, "CERT Advisory CA-1998-01: Smurf IP Denial-of-
              Service Attacks", 1998,
              <http://www.cert.org/advisories/CA-1998-01.html>.

   [Juniper2010]
              Juniper, "JunosE Software for E Series Broadband Services
              Routers Multicast Routing Configuration Guide", 2010, <htt
              p://www.juniper.net/techpubs/en_US/junose11.2/
              information-products/topic-collections/
              swconfig-multicast-routing/book-swconfig-multicast.pdf>.
















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Authors' Addresses

   Fernando Gont
   SI6 Networks / UTN-FRH
   Evaristo Carriego 2644
   Haedo, Provincia de Buenos Aires  1706
   Argentina

   Phone: +54 11 4650 8472
   Email: fgont@si6networks.com
   URI:   http://www.si6networks.com


   Will (Shucheng) Liu
   Huawei Technologies
   Bantian, Longgang District
   Shenzhen  518129
   P.R. China

   Email: liushucheng@huawei.com































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