Security Implications of Predictable Fragment Identification Values
draft-ietf-6man-predictable-fragment-id-06

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Document Type Active Internet-Draft (6man WG)
Last updated 2015-05-19
Replaces draft-gont-6man-predictable-fragment-id
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Intended RFC status Informational
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IPv6 maintenance Working Group (6man)                            F. Gont
Internet-Draft                                    SI6 Networks / UTN-FRH
Intended status: Informational                              May 18, 2015
Expires: November 19, 2015

  Security Implications of Predictable Fragment Identification Values
               draft-ietf-6man-predictable-fragment-id-06

Abstract

   IPv6 specifies the Fragment Header, which is employed for the
   fragmentation and reassembly mechanisms.  The Fragment Header
   contains an "Identification" field which, together with the IPv6
   Source Address and the IPv6 Destination Address of a packet,
   identifies fragments that correspond to the same original datagram,
   such that they can be reassembled together at the receiving host.
   The only requirement for setting the "Identification" value is that
   it must be different than that employed for any other fragmented
   packet sent recently with the same Source Address and Destination
   Address.  Some implementations use a simple global counter for
   setting the Identification field, thus leading to predictable values.
   This document analyzes the security implications of predictable
   Identification values, and provides implementation guidance for
   selecting the Identification field of the Fragment Header, such that
   the aforementioned security implications are mitigated.

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 November 19, 2015.

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Internet-Draft  Implications of Predictable Fragment IDs        May 2015

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
   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.  Security Implications of Predictable Fragment Identification
       values  . . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Constraints for the selection of Fragment Identification
       Values  . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   4.  Algorithms for Selecting Fragment Identification Values . . .   7
     4.1.  Per-destination counter (initialized to a random value) .   7
     4.2.  Randomized Identification values  . . . . . . . . . . . .   8
     4.3.  Hash-based Fragment Identification selection algorithm  .   8
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Appendix A.  Information leakage produced by vulnerable
                implementations  . . . . . . . . . . . . . . . . . .  13
   Appendix B.  Survey of Fragment Identification selection
                algorithms employed by popular IPv6 implementations   15
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  16

1.  Introduction

   IPv6 specifies the Fragment Header, which is employed for the
   fragmentation and reassembly mechanisms.  The Fragment Header
   contains an "Identification" field which, together with the IPv6
   Source Address and the IPv6 Destination Address of a packet,
   identifies fragments that correspond to the same original datagram,
   such that they can be reassembled together at the receiving host.
   The only requirement for setting the "Identification" value is that
   it must be different than that employed for any other fragmented

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