Processing of IPv6 "atomic" fragments
draft-ietf-6man-ipv6-atomic-fragments-02

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Document Type Active Internet-Draft (6man WG)
Last updated 2012-12-13 (latest revision 2012-11-06)
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IPv6 maintenance Working Group (6man)                            F. Gont
Internet-Draft                                       Huawei Technologies
Updates: 2460, 5722 (if approved)                       November 7, 2012
Intended status: Standards Track
Expires: May 11, 2013

                 Processing of IPv6 "atomic" fragments
                draft-ietf-6man-ipv6-atomic-fragments-02

Abstract

   The IPv6 specification allows packets to contain a Fragment Header
   without the packet being actually fragmented into multiple pieces.
   Such packets typically result from hosts that have received an ICMPv6
   "Packet Too Big" error message that advertises a "Next-Hop MTU"
   smaller than 1280 bytes, and are currently processed by some
   implementations as "fragmented traffic".  Thus, by forging ICMPv6
   "Packet Too Big" error messages an attacker can cause hosts to employ
   "atomic fragments", and then launch any fragmentation-based attacks
   against such traffic.  This document discusses the generation of the
   aforementioned "atomic fragments", the corresponding security
   implications, and formally updates RFC 2460 and RFC 5722 such that
   fragmentation-based attack vectors against traffic employing "atomic
   fragments" are completely eliminated.

Status of this Memo

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Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

Gont                      Expires May 11, 2013                  [Page 1]
Internet-Draft            IPv6 atomic fragments            November 2012

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Generation of IPv6 'atomic fragments'  . . . . . . . . . . . .  5
   3.  Updating RFC 2460 and RFC 5722 . . . . . . . . . . . . . . . .  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
   Appendix A.  Survey of processing of IPv6 atomic fragments by
                different operating systems . . . . . . . . . . . . . 12
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 13

Gont                      Expires May 11, 2013                  [Page 2]
Internet-Draft            IPv6 atomic fragments            November 2012

1.  Introduction

   [RFC2460] specifies the IPv6 fragmentation mechanism, which allows
   IPv6 packets to be fragmented into smaller pieces such that they fit
   in the Path-MTU to the intended destination(s).  [RFC2460] allowed
   fragments to overlap, thus leading to ambiguity in the result of the
   reassembly process, which could be leveraged by attackers to bypass
   firewall rules and/or evade Network Intrusion Detection Systems
   (NIDS) [RFC5722].

   [RFC5722] forbid overlapping fragments, specifying that when
   overlapping fragments are detected, all the fragments corresponding
   to that packet must be silently discarded.

   As specified in Section 5 of [RFC2460], when a host receives an
   ICMPv6 "Packet Too Big" message advertising a "Next-Hop MTU" smaller
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