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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 2460 (Obsoleted by RFC 8200) Summary: 1 error (**), 0 flaws (~~), 2 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 IPv6 maintenance Working Group (6man) F. Gont 3 Internet-Draft SI6 Networks / UTN-FRH 4 Updates: 2460 (if approved) V. Manral 5 Intended status: Standards Track Hewlett-Packard Corp. 6 Expires: August 20, 2012 February 17, 2012 8 Security and Interoperability Implications of Oversized IPv6 Header 9 Chains 10 draft-gont-6man-oversized-header-chain-00 12 Abstract 14 The IPv6 specification allows IPv6 header chains of an arbitrary 15 size. The specification also allows options which can in turn extend 16 each of the headers. In those scenarios in which the IPv6 header 17 chain or options are unusually long and packets are fragmented, or 18 scenarios in which the fragment size is very small, the first 19 fragment of a packet may fail to include the entire IPv6 header 20 chain. This document discusses the interoperability and security 21 problems of such traffic, and updates RFC 2460 such that all IPv6 22 packets are required to contain the entire IPv6 header chain within 23 the 'minimum IPv6 MTU' (1280) bytes of the packet. 25 Status of this Memo 27 This Internet-Draft is submitted in full conformance with the 28 provisions of BCP 78 and BCP 79. This document may not be modified, 29 and derivative works of it may not be created, and it may not be 30 published except as an Internet-Draft. 32 Internet-Drafts are working documents of the Internet Engineering 33 Task Force (IETF). Note that other groups may also distribute 34 working documents as Internet-Drafts. The list of current Internet- 35 Drafts is at http://datatracker.ietf.org/drafts/current/. 37 Internet-Drafts are draft documents valid for a maximum of six months 38 and may be updated, replaced, or obsoleted by other documents at any 39 time. It is inappropriate to use Internet-Drafts as reference 40 material or to cite them other than as "work in progress." 42 This Internet-Draft will expire on August 20, 2012. 44 Copyright Notice 46 Copyright (c) 2012 IETF Trust and the persons identified as the 47 document authors. All rights reserved. 49 This document is subject to BCP 78 and the IETF Trust's Legal 50 Provisions Relating to IETF Documents 51 (http://trustee.ietf.org/license-info) in effect on the date of 52 publication of this document. Please review these documents 53 carefully, as they describe your rights and restrictions with respect 54 to this document. Code Components extracted from this document must 55 include Simplified BSD License text as described in Section 4.e of 56 the Trust Legal Provisions and are provided without warranty as 57 described in the Simplified BSD License. 59 Table of Contents 61 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 62 2. Interoperability Implications of Oversized IPv6 Header 63 Chains . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 64 3. Forwarding Implications of Oversized IPv6 Header Chains . . . 5 65 4. Security Implications of Oversized IPv6 Header Chains . . . . 6 66 5. Updating RFC 2460 . . . . . . . . . . . . . . . . . . . . . . 7 67 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 68 7. Security Considerations . . . . . . . . . . . . . . . . . . . 9 69 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10 70 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 71 9.1. Normative References . . . . . . . . . . . . . . . . . . . 11 72 9.2. Informative References . . . . . . . . . . . . . . . . . . 11 73 Appendix A. Changes from previous versions of the document 74 (to be removed by the RFC Editor before 75 publication of this document as a RFC . . . . . . . . 12 76 A.1. Changes from draft-manral-6man-tiny-fragments-issues-00 . 12 77 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13 79 1. Introduction 81 [RFC2460] allows for an IPv6 header chain of an arbitrary size. It 82 also allows the headers themselves to have options, which can change 83 the size of the headers. In those scenarios in which the IPv6 header 84 chain is unusually long and packets are fragmented, or scenarios in 85 which the fragment size is very small, the first fragment of a packet 86 may fail to include the entire IPv6 header chain. This document 87 discusses the interoperability and security problems of such traffic, 88 and updates RFC 2460 such that all IPv6 packets are required to 89 contain the entire IPv6 header chain within the 'minimum IPv6 MTU' 90 (1280) bytes of the packet. 92 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 93 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 94 document are to be interpreted as described in RFC 2119 [RFC2119]. 96 2. Interoperability Implications of Oversized IPv6 Header Chains 98 Some transition technologies, such as NAT64 [RFC6146], may need to 99 have access to the entire IPv6 header chain in order to associate an 100 incoming IPv6 packet with an ongoing "session". 102 For instance, Section 3.4 of [RFC6146] states that "The NAT64 MAY 103 require that the UDP, TCP, or ICMP header be completely contained 104 within the fragment that contains fragment offset equal to zero". 106 Failure to include the entire IPv6 header chain in the first-fragment 107 may cause the translation function to fail, with the corresponding 108 packets being dropped. 110 3. Forwarding Implications of Oversized IPv6 Header Chains 112 A lot of the switches and Routers in the internet do hardware based 113 forwarding. To be able to achieve a level of throughput, there is a 114 fixed maximum number of clock cycles dedicated to each packet. 115 However with the use of unlimited options and header interleaving, 116 larger packets with a lot of interleaving have to be forwarded to the 117 software. It is for this reason that the maximum size of valid 118 packets with interleaved headers needs to be limited. 120 4. Security Implications of Oversized IPv6 Header Chains 122 Most firewalls enforce they filtering policy based on the following 123 parameters: 125 o Source IP address 127 o Destination IP address 129 o Protocol type 131 o Source port number 133 o Destination port number 135 Some firewalls reassemble fragmented packets before applying a 136 filtering policy, and thus always have the aforementioned information 137 available when deciding whether to allow or block a packet. However, 138 other stateless firewalls (generally prevalent on small/ home office 139 equipment) do not reassemble fragmented traffic, and hence have to 140 enforce their filtering policy based on the information contained in 141 the received fragment, as opposed to the information contained in the 142 reassembled datagram. 144 When presented with fragmented traffic, many of such firewalls 145 typically enforce their policy only on the first fragment of a 146 packet, based on the assumption that if the first fragment is 147 dropped, reassembly of the corresponding datagram will fail, and thus 148 such datagram will be effectively blocked. However, if the first 149 fragment fails to include the entire IPv6 header chain, they may have 150 no option other than "blindly" allowing or blocking the corresponding 151 fragment. If they blindly allow the packet, then the firewall can be 152 easily circumvented by intentionally sending fragmented packets that 153 fail to include the entire IPv6 header chain in the first fragment. 154 On the other hand, first-fragments that fail to include the entire 155 IPv6 header chain have never been formally deprecated and thus, in 156 theory, might be legitimately generated. 158 5. Updating RFC 2460 160 All IPv6 packets MUST contain the entire IPv6 header chain within the 161 first 1280 bytes of the packet. If a packet is fragmented, the first 162 fragment of the packet (i.e., that with a Fragment Offset of 0) must 163 contain the entire IPv6 header chain within the first 1280 bytes. 165 6. IANA Considerations 167 There are no IANA registries within this document. The RFC-Editor 168 can remove this section before publication of this document as an 169 RFC. 171 7. Security Considerations 173 This document describes the interoperability and security 174 implications of IPv6 packets or first-fragments that fail to include 175 the entire IPv6 header chain. The security implications include the 176 possibility of an attacker evading network security controls such as 177 firewalls and Network Intrusion Detection Systems (NIDS) [CPNI-IPv6]. 179 This document updates RFC 2460 such that those packets are forbidden, 180 thus preventing the aforementioned issues. 182 8. Acknowledgements 184 The authors would like to thank (in alphabetical order) XX for 185 providing valuable comments on earlier versions of this document. 187 9. References 189 9.1. Normative References 191 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 192 Requirement Levels", BCP 14, RFC 2119, March 1997. 194 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 195 (IPv6) Specification", RFC 2460, December 1998. 197 9.2. Informative References 199 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 200 NAT64: Network Address and Protocol Translation from IPv6 201 Clients to IPv4 Servers", RFC 6146, April 2011. 203 [CPNI-IPv6] 204 Gont, F., "Security Assessment of the Internet Protocol 205 version 6 (IPv6)", UK Centre for the Protection of 206 National Infrastructure, (available on request). 208 Appendix A. Changes from previous versions of the document (to be 209 removed by the RFC Editor before publication of this 210 document as a RFC 212 A.1. Changes from draft-manral-6man-tiny-fragments-issues-00 214 o The I-D was largely re-written. 216 o The current I-D notes that the problem lies in packets (or first- 217 fragments) missing the entire IPv6 header chain, rather than on 218 the (small) size of the fragments. 220 Authors' Addresses 222 Fernando Gont 223 SI6 Networks / UTN-FRH 224 Evaristo Carriego 2644 225 Haedo, Provincia de Buenos Aires 1706 226 Argentina 228 Phone: +54 11 4650 8472 229 Email: fgont@si6networks.com 230 URI: http://www.si6networks.com 232 Vishwas Manral 233 Hewlett-Packard Corp. 234 191111 Pruneridge Ave. 235 Cupertino, CA 95014 236 US 238 Phone: 408-447-1497 239 Email: vishwas.manral@hp.com