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: October 7, 2012 April 5, 2012 Security and Interoperability Implications of Oversized IPv6 Header Chains draft-gont-6man-oversized-header-chain-01 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 first "assumed Path-MTU" 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 This document may not be modified, and derivative works of it may not be created, and it may not be published except as an Internet-Draft.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 October 7, 2012. Copyright Notice Copyright (c) 2012 IETF Trust and the persons identified as the document authors. All rights reserved. Gont & Manral Expires October 7, 2012 [Page 1] Internet-Draft Implications of Oversized Header Chains April 2012 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-gont-6man-oversized-header-chain-00 . . 12 A.2. Changes from draft-manral-6man-tiny-fragments-issues-00 . 12 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13 Gont & Manral Expires October 7, 2012 [Page 2] Internet-Draft Implications of Oversized Header Chains April 2012 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 first "assumed Path- MTU" [RFC1981] [RFC4821] 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]. Gont & Manral Expires October 7, 2012 [Page 3] Internet-Draft Implications of Oversized Header Chains April 2012 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. Gont & Manral Expires October 7, 2012 [Page 4] Internet-Draft Implications of Oversized Header Chains April 2012 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. Gont & Manral Expires October 7, 2012 [Page 5] Internet-Draft Implications of Oversized Header Chains April 2012 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. Gont & Manral Expires October 7, 2012 [Page 6] Internet-Draft Implications of Oversized Header Chains April 2012 5. Updating RFC 2460 All IPv6 packets MUST contain the entire IPv6 header chain within the first "assumed Path-MTU" 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 "assumed Path-MTU" [RFC1981] [RFC4821] bytes of the packet. Nodes that do not implement Path-MTU Discovery [RFC1981] [RFC4821] must assume a Path-MTU of 1280 bytes (the minimum IPv6 MTU). Gont & Manral Expires October 7, 2012 [Page 7] Internet-Draft Implications of Oversized Header Chains April 2012 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. Gont & Manral Expires October 7, 2012 [Page 8] Internet-Draft Implications of Oversized Header Chains April 2012 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. Gont & Manral Expires October 7, 2012 [Page 9] Internet-Draft Implications of Oversized Header Chains April 2012 8. Acknowledgements The authors would like to thank (in alphabetical order) Dave Thaler for providing valuable comments on earlier versions of this document. Gont & Manral Expires October 7, 2012 [Page 10] Internet-Draft Implications of Oversized Header Chains April 2012 9. References 9.1. Normative References [RFC1981] McCann, J., Deering, S., and J. Mogul, "Path MTU Discovery for IP version 6", RFC 1981, August 1996. [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. [RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU Discovery", RFC 4821, March 2007. 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). Gont & Manral Expires October 7, 2012 [Page 11] Internet-Draft Implications of Oversized Header Chains April 2012 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-gont-6man-oversized-header-chain-00 o The I-D now requires all packets to contain the entire IPv6 header chain within the first "assumed Path-MTU" bytes of the packet (rather than "within the first 1280 bytes of the packet", as required by version -00 of this document). A.2. 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. Gont & Manral Expires October 7, 2012 [Page 12] Internet-Draft Implications of Oversized Header Chains April 2012 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 URI: Gont & Manral Expires October 7, 2012 [Page 13]