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Handling of Overlapping IPv6 Fragments
draft-ietf-6man-overlap-fragment-03

Revision differences

Document history

Date Rev. By Action
2012-08-22
03 (System) post-migration administrative database adjustment to the No Objection position for Cullen Jennings
2012-08-22
03 (System) post-migration administrative database adjustment to the No Objection position for Pasi Eronen
2012-08-22
03 (System) post-migration administrative database adjustment to the No Objection position for Dan Romascanu
2012-08-22
03 (System) post-migration administrative database adjustment to the No Objection position for Adrian Farrel
2012-08-22
03 (System) post-migration administrative database adjustment to the No Objection position for Lars Eggert
2009-11-30
03 Cindy Morgan State Changes to RFC Ed Queue from Approved-announcement sent by Cindy Morgan
2009-11-30
03 (System) IANA Action state changed to No IC from In Progress
2009-11-30
03 (System) IANA Action state changed to In Progress
2009-11-30
03 Amy Vezza IESG state changed to Approved-announcement sent
2009-11-30
03 Amy Vezza IESG has approved the document
2009-11-30
03 Amy Vezza Closed "Approve" ballot
2009-11-30
03 Jari Arkko State Changes to Approved-announcement to be sent from IESG Evaluation::External Party by Jari Arkko
2009-11-22
03 Adrian Farrel [Ballot Position Update] Position for Adrian Farrel has been changed to No Objection from Discuss by Adrian Farrel
2009-11-20
03 Samuel Weiler Request for Last Call review by SECDIR Completed. Reviewer: Carl Wallace.
2009-11-20
03 Dan Romascanu [Ballot Position Update] Position for Dan Romascanu has been changed to No Objection from Discuss by Dan Romascanu
2009-11-20
03 Jari Arkko State Changes to IESG Evaluation::External Party from IESG Evaluation::AD Followup by Jari Arkko
2009-11-20
03 Jari Arkko Waiting for the WG, Dan, and Adrian to agree to my suggested changes.
2009-11-20
03 (System) Removed from agenda for telechat - 2009-11-19
2009-11-19
03 Cindy Morgan State Changes to IESG Evaluation::AD Followup from IESG Evaluation by Cindy Morgan
2009-11-19
03 Lars Eggert [Ballot Position Update] Position for Lars Eggert has been changed to No Objection from Discuss by Lars Eggert
2009-11-19
03 Cullen Jennings [Ballot Position Update] Position for Cullen Jennings has been changed to No Objection from Discuss by Cullen Jennings
2009-11-19
03 Pasi Eronen [Ballot Position Update] Position for Pasi Eronen has been changed to No Objection from Discuss by Pasi Eronen
2009-11-18
03 Ross Callon [Ballot Position Update] New position, No Objection, has been recorded by Ross Callon
2009-11-18
03 Amy Vezza State Changes to IESG Evaluation from Waiting for AD Go-Ahead by Amy Vezza
2009-11-18
03 Lisa Dusseault [Ballot Position Update] New position, No Objection, has been recorded by Lisa Dusseault
2009-11-18
03 Tim Polk [Ballot Position Update] New position, No Objection, has been recorded by Tim Polk
2009-11-18
03 Ron Bonica [Ballot Position Update] New position, Yes, has been recorded by Ron Bonica
2009-11-18
03 Cullen Jennings
[Ballot discuss]
I agree with the basic recommendation of this draft that overlapping fragments should not be allowed (in v4 and v6) but I'm not …
[Ballot discuss]
I agree with the basic recommendation of this draft that overlapping fragments should not be allowed (in v4 and v6) but I'm not at all convinced by much of the rest of text. Was this reviewed by firewall people - my understanding tis the best practice in statefull inspection firewalls is to reconstruct the full packet. If this is true, the advice in the draft probably needs to be adjusted slightly.

I find this draft very confusing. Why would a firewall allow a packet in because the SYN= ACK=1. Are you aware of any firewalls that would actually do this when there had not be an outbound SYN first? Are there really commonly used firewalls that use 1858 ? The statefull inspection firewalls I have used reassembled the packet.

In section 4, what happens if you get a duplicate of a fragment? Is that an overlap causing discard?
2009-11-18
03 Cullen Jennings [Ballot Position Update] New position, Discuss, has been recorded by Cullen Jennings
2009-11-18
03 Magnus Westerlund [Ballot Position Update] New position, No Objection, has been recorded by Magnus Westerlund
2009-11-17
03 Ralph Droms [Ballot Position Update] New position, No Objection, has been recorded by Ralph Droms
2009-11-17
03 Dan Romascanu
[Ballot discuss]
The recommendation in section 4 includes:

>  When reassembling an IPv6 datagram, if
  one or more its constituent fragments is determined to …
[Ballot discuss]
The recommendation in section 4 includes:

>  When reassembling an IPv6 datagram, if
  one or more its constituent fragments is determined to be an
  overlapping fragment, the entire datagram (and any constituent
  fragments, including those not yet received), MUST be silently
  discarded.

It is not clear what 'silently' means here. It looks like the discards due to such overlapping datagrams should be counted and reflected through some management interface, which may chose to send notifications about the attack for every or whenever a number of such events is recorded. In this case the discard is not completely 'silent'.
2009-11-17
03 Dan Romascanu [Ballot Position Update] New position, Discuss, has been recorded by Dan Romascanu
2009-11-17
03 Adrian Farrel
[Ballot discuss]
I think this is a fine piece of work, but I have some difficulty
with the way it is positioned. It seems to …
[Ballot discuss]
I think this is a fine piece of work, but I have some difficulty
with the way it is positioned. It seems to be a little too timid about
updating the base IPv6 spec.

According to the Abstract, this document has two purposes:
- document the issues
- update 2460 to ban overlaps.
The Introduction, however, only talks about documenting the issues.

As far as I can see, the update to 2460 is actually more important than
the justification of the issues, so it would be good if the Introduction
was a little more fullsome.

But Section 4 is unclear. It is titled "Recommendation". If this work
truly updates 2460, this is not a recommendation; it is a protocol
modification.
2009-11-17
03 Adrian Farrel [Ballot Position Update] New position, Discuss, has been recorded by Adrian Farrel
2009-11-16
03 Russ Housley
[Ballot comment]
The Gen-ART Review by Francis Dupont on 29-Oct-2009 included a few
  editorial suggestions:

  - page 1: allows -> does not disallow?? …
[Ballot comment]
The Gen-ART Review by Francis Dupont on 29-Oct-2009 included a few
  editorial suggestions:

  - page 1: allows -> does not disallow??

  - page 2: Acknowledgements -> Acknowledgments

  - page 3: the term 'check' is not enough because it is for protection,
    something like 'security check' should be better (but a bit too
    strong).

- page 5: it is possible to get bad overlapping fragments from an error
  too (i.e., it is not always an attack, of course the action should be
  to drop the whole packet anyway).

- page 6: received), MUST -> received) MUST?

- page 6: Acknowledgements -> Acknowledgments
2009-11-16
03 Russ Housley [Ballot Position Update] New position, No Objection, has been recorded by Russ Housley
2009-11-15
03 Alexey Melnikov [Ballot Position Update] New position, No Objection, has been recorded by Alexey Melnikov
2009-11-03
03 Lars Eggert
[Ballot comment]
INTRODUCTION, paragraph 2:
>                  Handling of overlapping IPv6 fragments

  Imprecise title. This ID isn't …
[Ballot comment]
INTRODUCTION, paragraph 2:
>                  Handling of overlapping IPv6 fragments

  Imprecise title. This ID isn't about handling such fragments, it's
  about forbidding them.


Section 4.5, paragraph 0:
>    This document explores the issues
>    that can be caused by overlapping fragments.

  Last sentence should add the "and updates 2460..." bit from the
  abstract.


Section 3., paragraph 11:
>    The TCP header has the following values of the flags S(YN)=1 and
>    A(CK)=1.  This may make an inspecting stateful firewall think that it
>    is a response packet for a connection request initiated from the
>    trusted side of the firewall.  Hence it will allow the fragment to
>    pass.

  Stateful firewalls are called stateful because they track the
  transport protocol connection state. So a stateful firewall would
  *only* pass this packet *if* it was actually in response to a prior
  SYN in the opposiute direction. So I don't quite see how this attack
  is feasible.


Section 4., paragraph 1:
>    IPv6 nodes transmitting datagrams that need to be fragmented MUST NOT
>    create overlapping fragments.  When reassembling an IPv6 datagram, if
>    one or more its constituent fragments is determined to be an
>    overlapping fragment, the entire datagram (and any constituent
>    fragments, including those not yet received), MUST be silently
>    discarded.

  I agree that it must be discarded, but whether this is done silently
  is clearly a management decision of the local stack.


Section 5., paragraph 1:
>    This document discusses an attack that can be used to bypass IPv6
>    firewalls using overlapping fragments.  It recommends disallowing
>    overlapping fragments in order to prevent this attack.

  Imprecise language: It doesn't just "recommend" it, it makes it a
  requirement.
2009-11-03
03 Lars Eggert
[Ballot discuss]
Section 8., paragraph 1:
>    [RFC1858]  Ziemba, G., Reed, D., and P. Traina, "Security
>            …
[Ballot discuss]
Section 8., paragraph 1:
>    [RFC1858]  Ziemba, G., Reed, D., and P. Traina, "Security
>              Considerations for IP Fragment Filtering", RFC 1858,
>              October 1995.

  DISCUSS: ** Downref: Normative reference to an Informational RFC: RFC
  1858



Section 8., paragraph 4:
>    [RFC4942]  Davies, E., Krishnan, S., and P. Savola, "IPv6 Transition/
>              Co-existence Security Considerations", RFC 4942,
>              September 2007.

  DISCUSS: ** Downref: Normative reference to an Informational RFC: RFC
  4942
2009-11-03
03 Lars Eggert [Ballot Position Update] New position, Discuss, has been recorded by Lars Eggert
2009-11-02
03 (System) State has been changed to Waiting for AD Go-Ahead from In Last Call by system
2009-11-02
03 Pasi Eronen
[Ballot discuss]
I have reviewed draft-ietf-6man-overlap-fragment-03, and have one
question that I'd like to discuss before recommending approval of the
document:

I'm wondering why …
[Ballot discuss]
I have reviewed draft-ietf-6man-overlap-fragment-03, and have one
question that I'd like to discuss before recommending approval of the
document:

I'm wondering why the document does not recommend against (or
completely prohibit) excessively small first fragments (or in other
words, excessively small fragment offsets), similar to RFC 1858.

For example, splitting the TCP header to in the middle (with src/dst
port in one fragment, and the SYN/ACK/etc. flags in the other -- i.e.
Fragment Offset=1) seems to be still allowed by this draft.  But for
obvious reasons, it's quite likely to confuse firewalls.

(Of course, in IPv6 this situation cannot be completely ruled out,
since in theory at least, destination options can be larger than the
MTU. But that's unlikely to work in practice...)

(Perhaps this is something the WG discussed already; in that case,
I'd be interested in learning the rationale.)
2009-11-02
03 Pasi Eronen [Ballot Position Update] New position, Discuss, has been recorded by Pasi Eronen
2009-10-22
03 Samuel Weiler Request for Last Call review by SECDIR is assigned to Carl Wallace
2009-10-22
03 Samuel Weiler Request for Last Call review by SECDIR is assigned to Carl Wallace
2009-10-21
03 Amanda Baber IANA comments:

As described in the IANA Considerations section, we understand this
document to have NO IANA Actions.
2009-10-19
03 Amy Vezza Last call sent
2009-10-19
03 Amy Vezza State Changes to In Last Call from Last Call Requested by Amy Vezza
2009-10-16
03 Jari Arkko Placed on agenda for telechat - 2009-11-19 by Jari Arkko
2009-10-16
03 Jari Arkko Found no issues. Passing the document onwards.
2009-10-16
03 Jari Arkko Last Call was requested by Jari Arkko
2009-10-16
03 Jari Arkko State Changes to Last Call Requested from AD Evaluation by Jari Arkko
2009-10-16
03 Jari Arkko [Ballot Position Update] New position, Yes, has been recorded for Jari Arkko
2009-10-16
03 Jari Arkko Ballot has been issued by Jari Arkko
2009-10-16
03 Jari Arkko Created "Approve" ballot
2009-10-16
03 (System) Ballot writeup text was added
2009-10-16
03 (System) Last call text was added
2009-10-16
03 (System) Ballot approval text was added
2009-10-16
03 Jari Arkko State Changes to AD Evaluation from Publication Requested by Jari Arkko
2009-10-16
03 Cindy Morgan State Changes to Publication Requested from AD is watching by Cindy Morgan
2009-10-16
03 Cindy Morgan [Note]: 'Brian Haberman (brian@innovationslab.net) is the document shepherd.' added by Cindy Morgan
2009-10-16
03 Cindy Morgan
  (1.a) Who is the Document Shepherd for this document? Has the
        Document Shepherd personally reviewed this version of the
  …
  (1.a) Who is the Document Shepherd for this document? Has the
        Document Shepherd personally reviewed this version of the
        document and, in particular, does he or she believe this
        version is ready for forwarding to the IESG for publication?

Brian Haberman

  (1.b) Has the document had adequate review both from key WG members
        and from key non-WG members? Does the Document Shepherd have
        any concerns about the depth or breadth of the reviews that
        have been performed? 

This document has received adequete review and the shepherd does not
have any concerns with those reviews.

  (1.c) Does the Document Shepherd have concerns that the document
        needs more review from a particular or broader perspective,
        e.g., security, operational complexity, someone familiar with
        AAA, internationalization or XML?

No.

  (1.d) Does the Document Shepherd have any specific concerns or
        issues with this document that the Responsible Area Director
        and/or the IESG should be aware of? For example, perhaps he
        or she is uncomfortable with certain parts of the document, or
        has concerns whether there really is a need for it. In any
        event, if the WG has discussed those issues and has indicated
        that it still wishes to advance the document, detail those
        concerns here. Has an IPR disclosure related to this document
        been filed? If so, please include a reference to the
        disclosure and summarize the WG discussion and conclusion on
        this issue.

No concerns.

  (1.e) How solid is the WG consensus behind this document? Does it
        represent the strong concurrence of a few individuals, with
        others being silent, or does the WG as a whole understand and
        agree with it? 

The WG as a whole understands and supports this document.

  (1.f) Has anyone threatened an appeal or otherwise indicated extreme
        discontent? If so, please summarise the areas of conflict in
        separate email messages to the Responsible Area Director. (It
        should be in a separate email because this questionnaire is
        entered into the ID Tracker.)

No.

  (1.g) Has the Document Shepherd personally verified that the
        document satisfies all ID nits? (See the Internet-Drafts Checklist
        and http://tools.ietf.org/tools/idnits/). Boilerplate checks are
        not enough; this check needs to be thorough. Has the document
        met all formal review criteria it needs to, such as the MIB
        Doctor, media type and URI type reviews?

This version has 2 errors and 2 warnings from the id-nits check.  These
can be addressed when revisions are done for either IESG or IETF Last
Call comments.

  (1.h) Has the document split its references into normative and
        informative? Are there normative references to documents that
        are not ready for advancement or are otherwise in an unclear
        state? If such normative references exist, what is the
        strategy for their completion? Are there normative references
        that are downward references, as described in [RFC3967]? If
        so, list these downward references to support the Area
        Director in the Last Call procedure for them [RFC3967].

There are two downward references listed in the Normative references
section.

  (1.i) Has the Document Shepherd verified that the document IANA
        consideration section exists and is consistent with the body
        of the document? If the document specifies protocol
        extensions, are reservations requested in appropriate IANA
        registries? Are the IANA registries clearly identified? If
        the document creates a new registry, does it define the
        proposed initial contents of the registry and an allocation
        procedure for future registrations? Does it suggest a
        reasonable name for the new registry? See [RFC5226]. If the
        document describes an Expert Review process has Shepherd
        conferred with the Responsible Area Director so that the IESG
        can appoint the needed Expert during the IESG Evaluation?

There are no IANA actions for this document.

  (1.j) Has the Document Shepherd verified that sections of the
        document that are written in a formal language, such as XML
        code, BNF rules, MIB definitions, etc., validate correctly in
        an automated checker?

N/A.

  (1.k) The IESG approval announcement includes a Document
        Announcement Write-Up. Please provide such a Document
        Announcement Write-Up? Recent examples can be found in the
        "Action" announcements for approved documents. The approval
        announcement contains the following sections:

    Technical Summary
        The fragmentation and reassembly algorithm specified in the
        base IPv6 specification allows fragments to overlap.  This
        document demonstrates the security issues with allowing
        overlapping fragments and updates the IPv6 specification to
        explicitly forbid overlapping fragments.

    Working Group Summary
        The 6MAN working group has done extensive review of this
        document and it represents the strong consensus of the group.

    Document Quality
        This document has been reviewed by key members of the 6MAN
        working group and the chairs.
2009-10-16
03 Cindy Morgan Intended Status has been changed to Proposed Standard from None
2009-07-03
03 (System) New version available: draft-ietf-6man-overlap-fragment-03.txt
2009-03-09
02 (System) New version available: draft-ietf-6man-overlap-fragment-02.txt
2008-11-04
01 (System) New version available: draft-ietf-6man-overlap-fragment-01.txt
2008-10-27
03 Jari Arkko Draft Added by Jari Arkko in state AD is watching
2008-09-24
00 (System) New version available: draft-ietf-6man-overlap-fragment-00.txt