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Versions: (draft-gont-6man-oversized-header-chain) 00 01 02 03 04 05 06 07 08 09 RFC 7112

IPv6 maintenance Working Group (6man)                            F. Gont
Internet-Draft                                    SI6 Networks / UTN-FRH
Updates: 2460 (if approved)                                    V. Manral
Intended status: Standards Track                   Hewlett-Packard Corp.
Expires: May 9, 2013                                    November 5, 2012


  Security and Interoperability Implications of Oversized IPv6 Header
                                 Chains
               draft-ietf-6man-oversized-header-chain-02

Abstract

   The IPv6 specification allows IPv6 header chains of an arbitrary
   size.  The specification also allows options which can in turn extend
   each of the headers.  In those scenarios in which the IPv6 header
   chain or options are unusually long and packets are fragmented, or
   scenarios in which the fragment size is very small, the first
   fragment of a packet may fail to include the entire IPv6 header
   chain.  This document discusses the interoperability and security
   problems of such traffic, and updates RFC 2460 such that the first
   fragment of a packet is required to contain the entire IPv6 header
   chain.

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 May 9, 2013.

Copyright Notice

   Copyright (c) 2012 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



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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Interoperability Implications of Oversized IPv6 Header
       Chains . . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Forwarding Implications of Oversized IPv6 Header Chains  . . .  6
   5.  Security Implications of Oversized IPv6 Header Chains  . . . .  7
   6.  Updating RFC 2460  . . . . . . . . . . . . . . . . . . . . . .  8
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     10.1.  Normative References  . . . . . . . . . . . . . . . . . . 12
     10.2.  Informative References  . . . . . . . . . . . . . . . . . 12
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13


























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1.  Introduction

   With IPv6, IPv6 options are carried inside one or more IPv6 Extension
   Headers [RFC2460].  A sequence of more than one IPv6 Extension
   Headers in a row is commonly called an "IPv6 Header Chain".  In those
   scenarios in which the IPv6 header chain is unusually long and
   packets are fragmented, or scenarios in which the fragment size is
   very small, the first fragment of a packet may fail to include the
   entire IPv6 header chain.

   While IPv4 had a fixed maximum length for the set of all IPv4 options
   present in a single IPv4 packet, IPv6 does not have any equivalent
   maximum limit at present.  This document updates the set of IPv6
   specifications to create an overall limit on the size of the
   combination of IPv6 options and IPv6 Extension Headers that is
   allowed in a single IPv6 packet.  Namely, it updates RFC 2460 such
   that the first fragment of a fragmented datagram is required to
   contain the entire IPv6 header chain.

   It should be noted that this requirement does not preclude the use of
   e.g.  IPv6 jumbo payloads but instead merely requires that all
   *headers*, starting from IPv6 base header and continuing up to the
   upper layer header (e.g.  TCP or the like) be present in the first
   fragment.



























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2.  Terminology

   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].

   IPv6 Extension Headers:
      Any Extension Headers as described in Section 4 of [RFC2460], and
      specified in [RFC2460] or any subsequent documents.

   Entire IPv6 header chain:
      All protocol headers starting from the fixed IPv6 header up to
      (and including) the upper layer protocol header (TCP, UDP, etc. --
      assuming there is one of those), including any intermediate IPv6
      extension headers.

         Note: If there is an upper layer header, only the header (and
         not its payload) are considered part of the "entire IPv6 header
         chain".  For example, if the upper layer protocol is TCP, only
         the TCP header (and not its possible data bytes) should be
         considered part of the "entire IPv6 header chain".






























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3.  Interoperability Implications of Oversized IPv6 Header Chains

   Some transition technologies, such as NAT64 [RFC6146], might need to
   have access to the entire IPv6 header chain in order to associate an
   incoming IPv6 packet with an ongoing "session".

      For instance, Section 3.4 of [RFC6146] states that "The NAT64 MAY
      require that the UDP, TCP, or ICMP header be completely contained
      within the fragment that contains fragment offset equal to zero".

   Failure to include the entire IPv6 header chain in the first-fragment
   might cause the translation function to fail, with the corresponding
   packets being dropped.






































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4.  Forwarding Implications of Oversized IPv6 Header Chains

   A lot of the switches and Routers in the internet do hardware based
   forwarding.  To be able to achieve a level of throughput, there is a
   fixed maximum number of clock cycles dedicated to each packet.
   However with the use of unlimited options and header interleaving,
   larger packets with a lot of interleaving might have to be forwarded
   to the software.  This is one reason why the maximum size of valid
   packets with interleaved headers needs to be limited.










































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5.  Security Implications of Oversized IPv6 Header Chains

   Most firewalls enforce their filtering policy based on the following
   parameters:

   o  Source IP address

   o  Destination IP address

   o  Protocol type (e.g.  ICMPv6, TCP, UDP, SCTP)

   o  Transport-layer Source Port number

   o  Transport-layer Destination Port number

   Some firewalls reassemble fragmented packets before applying a
   filtering policy, and thus always have the aforementioned information
   available when deciding whether to allow or block a packet.  However,
   other stateless firewalls (generally prevalent on small/ home office
   equipment) do not reassemble fragmented traffic, and hence have to
   enforce their filtering policy based on the information contained in
   the received fragment, as opposed to the information contained in the
   reassembled datagram.

   When presented with fragmented traffic, many of such firewalls
   typically enforce their policy only on the first fragment of a
   packet, based on the assumption that if the first fragment is
   dropped, reassembly of the corresponding datagram will fail, and thus
   such datagram will be effectively blocked.  However, if the first
   fragment fails to include the entire IPv6 header chain, they might
   have no alternative other than "blindly" allowing or blocking the
   corresponding fragment.  If they blindly allow the packet, then the
   firewall can be easily circumvented by intentionally sending
   fragmented packets that fail to include the entire IPv6 header chain
   in the first fragment.  On the other hand, first-fragments that fail
   to include the entire IPv6 header chain have never been formally
   deprecated and thus, in theory, might be legitimately generated.














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6.  Updating RFC 2460

   If an IPv6 packet is fragmented, the first fragment of that IPv6
   packet (i.e., the fragment having a Fragment Offset of 0) MUST
   contain the entire IPv6 header chain.

   A host that receives an IPv6 first-fragment that does not contain the
   entire IPv6 header chain SHOULD drop that packet, and also MAY send
   an ICMPv6 error message to the (claimed) source address (subject to
   the sending rules for ICMPv6 errors specified in [RFC4443]).

   An intermediate system (e.g. router, firewall) that receives an IPv6
   first-fragment that does not contain the entire IPv6 header chain MAY
   drop that packet, and MAY send an ICMPv6 error message to the
   (claimed) source address (subject to the sending rules for ICMPv6
   error messages specified in [RFC4443]).  Intermediate systems having
   this capability SHOULD support configuration (e.g. enable/disable) of
   whether such packets are dropped or not by the intermediate system.

   If a host or intermediate system drops an IPv6 first-fragment because
   it does not contain the entire IPv6 Header Chain, and sends an ICMPv6
   error message due to that packet drop, then the ICMPv6 error message
   MUST be Type 4 ("Parameter Problem") and MUST use Code 3 ("First-
   fragment has incomplete IPv6 Header Chain").

   Implementations SHOULD support configuration of whether an ICMPv6
   error/diagnostic message is sent when such packet drops occur.
   Implementations might consider providing not only an enable/disable
   configuration, but also other settings (e.g. rate-limit the sending
   of this kind of ICMPv6 error message).

   Sending this ICMPv6 error message when such packets are dropped can
   be very helpful in diagnosing operational IPv6 network problems, for
   example if recursive tunnels or certain link technologies have
   reduced the end-to-end MTU from larger more common values.  However,
   such ICMPv6 messages also might be operationally problematic, for
   example if an adversary forges the source address on IPv6 first-
   fragment packets that do NOT contain the entire IPv6 Header Chain.
   So configurability about sending these ICMPv6 error messages is very
   important to network operators for this situation.











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7.  IANA Considerations

   IANA is requested that the "Reason Code" registry for ICMPv6 "Type 4
   - Parameter Problem" messages be updated as follows:

      CODE     NAME/DESCRIPTION
        3      IPv6 first-fragment has incomplete IPv6 header chain












































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8.  Security Considerations

   This document describes the interoperability and security
   implications of IPv6 packets or first-fragments that fail to include
   the entire IPv6 header chain.  The security implications include the
   possibility of an attacker evading network security controls such as
   firewalls and Network Intrusion Detection Systems (NIDS) [CPNI-IPv6].

   This document updates RFC 2460 such that those packets are forbidden,
   thus preventing the aforementioned issues.

   This specification allows nodes that drop the aforementioned packets
   to signal such packet drops with ICMPv6 "Parameter Problem, IPv6
   first-fragment has incomplete IPv6 header chain" (Type 4, Code 3)
   error messages.

   As with all ICMPv6 error/diagnostic messages, deploying Source
   Address Forgery Prevention filters helps reduce the chances of an
   attacker successfully performing a reflection attack by sending
   forged illegal packets with the victim/target's IPv6 address as the
   IPv6 Source Address of the illegal packet [RFC2827] [RFC3704].






























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9.  Acknowledgements

   The authors of this document would like to thank Ran Atkinson for
   contributing text and ideas that were incorporated into this
   document.

   The authors would like to thank (in alphabetical order) Ran Atkinson,
   Fred Baker, Dominik Elsbroek, Bill Jouris, Suresh Krishnan, Dave
   Thaler, and Eric Vyncke, for providing valuable comments on earlier
   versions of this document.









































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10.  References

10.1.  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.

10.2.  Informative References

   [RFC2827]  Ferguson, P. and D. Senie, "Network Ingress Filtering:
              Defeating Denial of Service Attacks which employ IP Source
              Address Spoofing", BCP 38, RFC 2827, May 2000.

   [RFC3704]  Baker, F. and P. Savola, "Ingress Filtering for Multihomed
              Networks", BCP 84, RFC 3704, March 2004.

   [RFC6146]  Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
              NAT64: Network Address and Protocol Translation from IPv6
              Clients to IPv4 Servers", RFC 6146, April 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).




















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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


   Vishwas Manral
   Hewlett-Packard Corp.
   191111 Pruneridge Ave.
   Cupertino, CA  95014
   US

   Phone: 408-447-1497
   Email: vishwas.manral@hp.com
   URI:





























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