Security Implications of Predictable Fragment Identification Values
draft-ietf-6man-predictable-fragment-id-09

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Document Type Active Internet-Draft (6man WG)
Last updated 2015-09-14 (latest revision 2015-08-25)
Replaces draft-gont-6man-predictable-fragment-id
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IPv6 maintenance Working Group (6man)                            F. Gont
Internet-Draft                                    SI6 Networks / UTN-FRH
Intended status: Informational                           August 25, 2015
Expires: February 26, 2016

  Security Implications of Predictable Fragment Identification Values
               draft-ietf-6man-predictable-fragment-id-09

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 by the receiving host.
   The only requirement for setting the "Identification" field is that
   the corresponding value 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 Identification 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
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   material or to cite them other than as "work in progress."

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

Gont                    Expires February 26, 2016               [Page 1]
Internet-Draft  Implications of Predictable Fragment IDs     August 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
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   include Simplified BSD License text as described in Section 4.e of
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Security Implications of Predictable Fragment Identification
       values  . . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Constraints for the selection of Fragment Identification
       Values  . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Algorithms for Selecting Fragment Identification Values . . .   7
     5.1.  Per-destination counter (initialized to a random value) .   7
     5.2.  Randomized Identification values  . . . . . . . . . . . .   9
     5.3.  Hash-based Fragment Identification selection algorithm  .   9
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  12
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  13
   Appendix A.  Information leakage produced by vulnerable
                implementations  . . . . . . . . . . . . . . . . . .  15
   Appendix B.  Survey of Fragment Identification selection
                algorithms employed by popular IPv6 implementations   17
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  18

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
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