draft-ietf-6man-overlap-fragment-01.txt   draft-ietf-6man-overlap-fragment-02.txt 
6man Working Group S. Krishnan 6man Working Group S. Krishnan
Internet-Draft Ericsson Internet-Draft Ericsson
Updates: 2460 (if approved) November 3, 2008 Updates: 2460 (if approved) March 8, 2009
Intended status: Standards Track Intended status: Standards Track
Expires: May 7, 2009 Expires: September 9, 2009
Handling of overlapping IPv6 fragments Handling of overlapping IPv6 fragments
draft-ietf-6man-overlap-fragment-01 draft-ietf-6man-overlap-fragment-02
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Abstract Abstract
The fragmentation and reassembly algorithm specified in the base IPv6 The fragmentation and reassembly algorithm specified in the base IPv6
specification allows fragments to overlap. This document specification allows fragments to overlap. This document
demonstrates the security issues with allowing overlapping fragments demonstrates the security issues with allowing overlapping fragments
and updates the IPv6 specification to explicitly forbid overlapping and updates the IPv6 specification to explicitly forbid overlapping
fragments. fragments.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions used in this document . . . . . . . . . . . . . 3 1.1. Conventions used in this document . . . . . . . . . . . . . 3
2. Overlapping Fragments . . . . . . . . . . . . . . . . . . . . . 3 2. Overlapping Fragments . . . . . . . . . . . . . . . . . . . . . 3
3. The attack . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. The attack . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Recommendation . . . . . . . . . . . . . . . . . . . . . . . . 5 4. Recommendation . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
7. Normative References . . . . . . . . . . . . . . . . . . . . . 6 7. Normative References . . . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 6 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 7
Intellectual Property and Copyright Statements . . . . . . . . . . 7
1. Introduction 1. Introduction
Fragmentation is used in IPv6 when the IPv6 packet will not fit Fragmentation is used in IPv6 when the IPv6 packet will not fit
inside the path MTU to its destination. When fragmentation is inside the path MTU to its destination. When fragmentation is
performed an IPv6 node uses a fragment header as specified in section performed an IPv6 node uses a fragment header as specified in section
4.5 of the IPv6 base specification [RFC2460] to break down the 4.5 of the IPv6 base specification [RFC2460] to break down the
datagram into smaller fragments that will fit in the path MTU. The datagram into smaller fragments that will fit in the path MTU. The
destination node receives these fragments and reassembles them. The destination node receives these fragments and reassembles them. The
algorithm specified for fragmentation in [RFC2460] does not prevent algorithm specified for fragmentation in [RFC2460] does not prevent
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Note that this attack is much more serious in IPv6 than in IPv4. In Note that this attack is much more serious in IPv6 than in IPv4. In
IPv4 the overlapping part of the TCP header did not include the IPv4 the overlapping part of the TCP header did not include the
source and destination ports. In IPv6 the attack can easily work to source and destination ports. In IPv6 the attack can easily work to
replace the source or destination port with an overlapping fragment. replace the source or destination port with an overlapping fragment.
4. Recommendation 4. Recommendation
IPv6 nodes transmitting datagrams that need to be fragmented MUST NOT IPv6 nodes transmitting datagrams that need to be fragmented MUST NOT
create overlapping fragments. IPv6 nodes that receive a fragment create overlapping fragments. IPv6 nodes that receive a fragment
that overlaps with a previously received fragment MUST cease the that overlaps with a previously received fragment MUST cease the
reassembly process and MUST ignore further fragments with the same reassembly process and MUST discard the previously received fragments
IPv6 Source Address, IPv6 Destination Address and Fragment with the same IPv6 Source Address, IPv6 Destination Address and
Identification. It MUST also discard the previously received Fragment Identification.
fragments with the same IPv6 Source Address, IPv6 Destination Address
and Fragment Identification.
5. Security Considerations 5. Security Considerations
This document discusses an attack that can be used to bypass IPv6 This document discusses an attack that can be used to bypass IPv6
firewalls using overlapping fragments. It recommends disallowing firewalls using overlapping fragments. It recommends disallowing
overlapping fragments in order to prevent this attack. overlapping fragments in order to prevent this attack.
6. IANA Considerations 6. IANA Considerations
This document does not require any action from the IANA. This document does not require any action from the IANA.
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Author's Address Author's Address
Suresh Krishnan Suresh Krishnan
Ericsson Ericsson
8400 Blvd Decarie 8400 Blvd Decarie
Town of Mount Royal, Quebec Town of Mount Royal, Quebec
Canada Canada
Email: suresh.krishnan@ericsson.com Email: suresh.krishnan@ericsson.com
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