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Versions: 00 01                                                         
IP Multicast                                                   E. Vyncke
Internet-Draft                                                     Cisco
Intended status: Informational                                    E. Rey
Expires: June 26, 2016                                              ERNW
                                                              A. Atlasis
                                                              NCI Agency
                                                       December 24, 2015


                              MLD Security
                    draft-vyncke-pim-mld-security-01

Abstract

   The latest version of Multicast Listener Discovery protocol is
   defined in RFC 3810, dated back in 2004, while the first version of
   MLD, which is still in use and has not been deprecated, is defined in
   RFC 2710 and is dated back in 1999.  New security research has
   exhibited new vulnerabilities in MLD, both remote and local attack
   vectors.  This document describes those vulnerabilities and proposes
   specific mitigation techniques.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on June 26, 2016.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   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



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   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Local Vulnerabilities . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Downgrading to MLDv1  . . . . . . . . . . . . . . . . . .   3
     2.2.  Queries sent to unicast address . . . . . . . . . . . . .   4
     2.3.  Win the election  . . . . . . . . . . . . . . . . . . . .   4
     2.4.  Host enumeration and OS fingerprinting  . . . . . . . . .   4
     2.5.  Flooding of MLD messages  . . . . . . . . . . . . . . . .   4
     2.6.  Amplification . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Remote Vulnerabilities  . . . . . . . . . . . . . . . . . . .   5
   4.  Mitigations . . . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   The Multicast Listener Discovery protocol version 2 (MLDv2) RFC3810
   [RFC3810] has a security section but it was not exhaustive and the
   focus was only on local forged MLD packets.  The same is also true
   for the first version of MLD (now called MLDv1), which is still in
   use, defined in RFC 2710.  This document goes beyond those attacks.

   For the reader who is not familiar with MLDv2, here are the main
   points:

      Multicast routers send MLD queries which are either generic (query
      about all multicast group) sent to ff02::1 (link-scope all nodes)
      or specific (query about a specific group) sent to this multicast
      group.  Query messages can also be sent to a unicast address.

      Multicast members reply to MLDv2 queries with reports sent to
      ff02::16 (link-scope all MDLDv2 routers).  In version 1 of MLD
      RFC2710 [RFC2710], the reports are sent to the multicast group
      being reported.  Reports can be transmitted twice or more in order
      to ensure that the MLD router gets at least one report.




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      When a node ceases to listen to a multicast address on an
      interface, it sends an MLDv1 Done message or a specially crafted
      MLDv2 Report message.

      All MLD packets are ICMPv6 RFC4443 [RFC4443] messages sent with a
      hop-limit of 1, from a link-local address and there is no
      authentication.

      MLD messages received with a hop-limit greater than 1 should be
      discarded.

      Neighbor Discovery Protocol RFC4861 [RFC4861] requires nodes to
      become member of the respective solicited-node multicast groups
      for all their link-scope and global-scope addresses.

      Switches are assumed to implement MLD snooping RFC4541 [RFC4541]
      to learn where to forward multicast packets.  It must be noted
      though that implementations of MLD snooping do not act on link-
      local multicast groups such as solicited-node multicast group:
      they simply forward all packets destined to a link-local multicast
      group to all port in the same layer-2 network.

      MLDv2 was designed to be interoperable with MLDv1.

      The main difference between MLDv1 and MLDv2 from a functionality
      perspective is that MLDv1 does not support "source filtering" (in
      MLDv2 nodes can report interest in traffic only from a set of
      source addresses or from all except a set source addresses).

      Every IPv6 node must support MLD.

   This document is heavily based on previous research: [Troopers2015].

2.  Local Vulnerabilities

2.1.  Downgrading to MLDv1

   A single MLDv1 report message is enough to downgrade all MLD nodes
   (hosts and routers) to the version 1 protocol.  This could be used to
   force a MLD host to reply with MLDv1 reports sent to the multicast
   group rather than to ff02::16.  This downgrade to MLDv1 could also be
   used to transmit the MLDv1 report with a 'done' operation to remove a
   listener (stopping the multicast traffic on the subnet).  Another
   consequence of downgrading to MLDv1 can be the fact that an attacker
   can also used "Host Suppression" feature as part of a DoS attack,
   make the launch of such an attack easier.





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2.2.  Queries sent to unicast address

   Section 5.1.15 of RFC3810 [RFC3810], specifies that for debugging
   purposes, nodes must accept and process queries sent to any of their
   addresses (including unicast).  Lab testing, described in
   [Troopers2015], clearly shows that all implementations except FreeBSD
   accept and process MLD queries sent to a unicast global address.
   This can be an exploited to completely bypass the legitimate MLD
   router and interact directly (for whatever purpose) with the targets
   (including legitimate routers and clients).

2.3.  Win the election

   When there are multiple MLD routers in a layer-2 domain, the one with
   the lowest IPv6 address wins the election and becomes the designated
   MLD router.  A hostile node can then send from a lower link-local
   address an MLD message and become the MLD router.  This fact in
   combination with the direct interaction with the targets could be
   leveraged to mount a denial of service attack.

2.4.  Host enumeration and OS fingerprinting

   Some hosts try to prevent host enumeration by not responding to
   ICMPv6 echo request messages sent to any multicast group.  But, the
   same hosts must reply to any MLD queries including the generic one
   sent to ff02::1, this allows for MLD host enumeration.  As hosts join
   different groups based on their operating system (specific groups for
   Microsoft Windows for example), the MLD report can also help for
   Operating System (OS) fingerprinting.

2.5.  Flooding of MLD messages

   If an implementation does not rate limit in hardware the rate of
   processed MLD messages, then they are vulnerable to a CPU exhaustion
   denial of services.  If a node does not limit the number of states
   associated to MLD, then this node is vulnerable to a memory
   exhaustion denial of services.

2.6.  Amplification

   Nodes usually join multiple groups (for example, Microsoft Windows
   8.1 joins 4 groups).  Therefore a forged generic MLDv1 query will
   force those nodes to transmit MLDv1 reports for each of their groups
   (in our example 4); furthermore, many implementations send MLD
   reports twice (in our example 8 in total).  MLDv2 is a little better
   because reports are sent to ff02::16 and not to the multicast group.





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3.  Remote Vulnerabilities

   MLD messages with hop-limit different than 1 should be discarded but
   nothing prevents a hostile party located n hops away from the victim
   to send any MLD messages with a hop-limit set to n+1.  Therefore, a
   remote hostile party can mount attacks against MLD (especially
   because implementations process MLD queries sent to a global unicast
   address).

4.  Mitigations

   This section proposes some mitigation techniques that could be used
   to prevent the above attacks.  This section is not a specification of
   any kind, the words 'should' is plain English and is not related to
   RFC2119 [RFC2119].

   Mitigation by specific implementations:

      Similar to RA-guard RFC6105 [RFC6105], there should be a MLD-guard
      function in layer-2 switches; MLD queries (either version 1 or
      version 2) received on ports attached to non multicast routers
      should be discarded.  Switches could also block all MLDv1 packets
      in order to prevent the downgrading of MLD version.  Of course,
      this requires all nodes to support MLDv2.

      All nodes should be able to disable MLDv1.

      Control plane policing should also be implemented in order to
      avoid denial of services attacks.

   Mitigation by a protocol update of RFC2710 [RFC2710] and RFC3810
   [RFC3810]:

      MLD queries should not be accepted and processed when sent to a
      unicast address (either link-local or global scope).  This
      requires update of RFC 3810 and RFC 2710.

      To mitigate the remote attacks, the hop-limit should have been set
      to 255 and MLD nodes should discard packets with a hop-limit
      different than 255.

5.  IANA Considerations

   This document contains no IANA considerations.







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6.  Security Considerations

   Thi document describes multiple vulnerabilities that have been
   described above and tries to mitigate them or even eliminate some of
   them by making specific suggestions for update of the protocol as
   well as by suggesting the implementation of related security
   mechanisms to layer-2 devices.

7.  Acknowledgements

   The authors would like to thank Stig Venaas for some discussions on
   this topic.

8.  References

8.1.  Normative References

   [RFC2710]  Deering, S., Fenner, W., and B. Haberman, "Multicast
              Listener Discovery (MLD) for IPv6", RFC 2710,
              DOI 10.17487/RFC2710, October 1999,
              <http://www.rfc-editor.org/info/rfc2710>.

   [RFC3810]  Vida, R., Ed. and L. Costa, Ed., "Multicast Listener
              Discovery Version 2 (MLDv2) for IPv6", RFC 3810,
              DOI 10.17487/RFC3810, June 2004,
              <http://www.rfc-editor.org/info/rfc3810>.

8.2.  Informative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC4443]  Conta, A., Deering, S., and M. Gupta, Ed., "Internet
              Control Message Protocol (ICMPv6) for the Internet
              Protocol Version 6 (IPv6) Specification", RFC 4443,
              DOI 10.17487/RFC4443, March 2006,
              <http://www.rfc-editor.org/info/rfc4443>.

   [RFC4541]  Christensen, M., Kimball, K., and F. Solensky,
              "Considerations for Internet Group Management Protocol
              (IGMP) and Multicast Listener Discovery (MLD) Snooping
              Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006,
              <http://www.rfc-editor.org/info/rfc4541>.






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   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              DOI 10.17487/RFC4861, September 2007,
              <http://www.rfc-editor.org/info/rfc4861>.

   [RFC6105]  Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and J.
              Mohacsi, "IPv6 Router Advertisement Guard", RFC 6105,
              DOI 10.17487/RFC6105, February 2011,
              <http://www.rfc-editor.org/info/rfc6105>.

   [Troopers2015]
              Rey, E., Atlasis, A., and J. Salazar, "MLD Considered
              Harmful", 2015, <https://www.troopers.de/media/
              filer_public/7c/35/7c35967a-d0d4-46fb-8a3b-4c16df37ce59/tr
              oopers15_ipv6secsummit_atlasis_rey_salazar_mld_considered_
              harmful_final.pdf>.

Authors' Addresses

   Eric Vyncke
   Cisco
   De Kleetlaan 6a
   Diegem  1831
   Belgium

   Phone: +32 2 778 4677
   Email: evyncke@cisco.com


   Enno Rey
   ERNW
   Carl-Bosch-Str. 4
   Heidelberg  69115
   Germany

   Phone: +49 6221 480390
   Email: erey@ernw.de


   Antonios Atlasis
   NCI Agency
   Oude Waalsdorperweg 61
   The Hague  2597 AK
   The Netherlands

   Phone: +31 703743564
   Email: antonios.atlasis@ncia.nato.int




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