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IETF I-D: Implications Of Oversized IPv6 Header Chains

IETF I-D: Implications Of Oversized IPv6 Header Chains
Posted Feb 18, 2012
Authored by Fernando Gont

This IETF Internet Draft discusses security and interoperability implications of oversized IPv6 header chains.

tags | paper
SHA-256 | 8ec27e6f6b09e69798fd08859eb67352a7f027ed6076d6512288a35a48b32023

IETF I-D: Implications Of Oversized IPv6 Header Chains

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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: August 20, 2012 February 17, 2012


Security and Interoperability Implications of Oversized IPv6 Header
Chains
draft-gont-6man-oversized-header-chain-00

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 all IPv6
packets are required to contain the entire IPv6 header chain within
the 'minimum IPv6 MTU' (1280) bytes of the packet.

Status of this Memo

This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. This document may not be modified,
and derivative works of it may not be created, and it may not be
published except as an Internet-Draft.

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 August 20, 2012.

Copyright Notice

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




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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 . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Interoperability Implications of Oversized IPv6 Header
Chains . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Forwarding Implications of Oversized IPv6 Header Chains . . . 5
4. Security Implications of Oversized IPv6 Header Chains . . . . 6
5. Updating RFC 2460 . . . . . . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
9.1. Normative References . . . . . . . . . . . . . . . . . . . 11
9.2. Informative References . . . . . . . . . . . . . . . . . . 11
Appendix A. Changes from previous versions of the document
(to be removed by the RFC Editor before
publication of this document as a RFC . . . . . . . . 12
A.1. Changes from draft-manral-6man-tiny-fragments-issues-00 . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13





















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1. Introduction

[RFC2460] allows for an IPv6 header chain of an arbitrary size. It
also allows the headers themselves to have options, which can change
the size of the headers. 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. This document
discusses the interoperability and security problems of such traffic,
and updates RFC 2460 such that all IPv6 packets are required to
contain the entire IPv6 header chain within the 'minimum IPv6 MTU'
(1280) bytes of the packet.

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].



































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2. Interoperability Implications of Oversized IPv6 Header Chains

Some transition technologies, such as NAT64 [RFC6146], may 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
may cause the translation function to fail, with the corresponding
packets being dropped.






































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3. 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 have to be forwarded to the
software. It is for this reason that the maximum size of valid
packets with interleaved headers needs to be limited.










































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4. Security Implications of Oversized IPv6 Header Chains

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

o Source IP address

o Destination IP address

o Protocol type

o Source port number

o 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 may have
no option 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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5. Updating RFC 2460

All IPv6 packets MUST contain the entire IPv6 header chain within the
first 1280 bytes of the packet. If a packet is fragmented, the first
fragment of the packet (i.e., that with a Fragment Offset of 0) must
contain the entire IPv6 header chain within the first 1280 bytes.













































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6. IANA Considerations

There are no IANA registries within this document. The RFC-Editor
can remove this section before publication of this document as an
RFC.














































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7. 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.









































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8. Acknowledgements

The authors would like to thank (in alphabetical order) XX for
providing valuable comments on earlier versions of this document.















































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9. References

9.1. 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.

9.2. Informative References

[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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Appendix A. Changes from previous versions of the document (to be
removed by the RFC Editor before publication of this
document as a RFC

A.1. Changes from draft-manral-6man-tiny-fragments-issues-00

o The I-D was largely re-written.

o The current I-D notes that the problem lies in packets (or first-
fragments) missing the entire IPv6 header chain, rather than on
the (small) size of the fragments.








































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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






























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