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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 1981 (Obsoleted by RFC 8201) ** Obsolete normative reference: RFC 2460 (Obsoleted by RFC 8200) Summary: 2 errors (**), 0 flaws (~~), 1 warning (==), 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: October 7, 2012 April 5, 2012 8 Security and Interoperability Implications of Oversized IPv6 Header 9 Chains 10 draft-gont-6man-oversized-header-chain-01 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 first "assumed Path-MTU" 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 October 7, 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-gont-6man-oversized-header-chain-00 . . 12 77 A.2. Changes from draft-manral-6man-tiny-fragments-issues-00 . 12 78 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13 80 1. Introduction 82 [RFC2460] allows for an IPv6 header chain of an arbitrary size. It 83 also allows the headers themselves to have options, which can change 84 the size of the headers. In those scenarios in which the IPv6 header 85 chain is unusually long and packets are fragmented, or scenarios in 86 which the fragment size is very small, the first fragment of a packet 87 may fail to include the entire IPv6 header chain. This document 88 discusses the interoperability and security problems of such traffic, 89 and updates RFC 2460 such that all IPv6 packets are required to 90 contain the entire IPv6 header chain within the first "assumed Path- 91 MTU" [RFC1981] [RFC4821] bytes of the packet. 93 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 94 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 95 document are to be interpreted as described in RFC 2119 [RFC2119]. 97 2. Interoperability Implications of Oversized IPv6 Header Chains 99 Some transition technologies, such as NAT64 [RFC6146], may need to 100 have access to the entire IPv6 header chain in order to associate an 101 incoming IPv6 packet with an ongoing "session". 103 For instance, Section 3.4 of [RFC6146] states that "The NAT64 MAY 104 require that the UDP, TCP, or ICMP header be completely contained 105 within the fragment that contains fragment offset equal to zero". 107 Failure to include the entire IPv6 header chain in the first-fragment 108 may cause the translation function to fail, with the corresponding 109 packets being dropped. 111 3. Forwarding Implications of Oversized IPv6 Header Chains 113 A lot of the switches and Routers in the internet do hardware based 114 forwarding. To be able to achieve a level of throughput, there is a 115 fixed maximum number of clock cycles dedicated to each packet. 116 However with the use of unlimited options and header interleaving, 117 larger packets with a lot of interleaving have to be forwarded to the 118 software. It is for this reason that the maximum size of valid 119 packets with interleaved headers needs to be limited. 121 4. Security Implications of Oversized IPv6 Header Chains 123 Most firewalls enforce they filtering policy based on the following 124 parameters: 126 o Source IP address 128 o Destination IP address 130 o Protocol type 132 o Source port number 134 o Destination port number 136 Some firewalls reassemble fragmented packets before applying a 137 filtering policy, and thus always have the aforementioned information 138 available when deciding whether to allow or block a packet. However, 139 other stateless firewalls (generally prevalent on small/ home office 140 equipment) do not reassemble fragmented traffic, and hence have to 141 enforce their filtering policy based on the information contained in 142 the received fragment, as opposed to the information contained in the 143 reassembled datagram. 145 When presented with fragmented traffic, many of such firewalls 146 typically enforce their policy only on the first fragment of a 147 packet, based on the assumption that if the first fragment is 148 dropped, reassembly of the corresponding datagram will fail, and thus 149 such datagram will be effectively blocked. However, if the first 150 fragment fails to include the entire IPv6 header chain, they may have 151 no option other than "blindly" allowing or blocking the corresponding 152 fragment. If they blindly allow the packet, then the firewall can be 153 easily circumvented by intentionally sending fragmented packets that 154 fail to include the entire IPv6 header chain in the first fragment. 155 On the other hand, first-fragments that fail to include the entire 156 IPv6 header chain have never been formally deprecated and thus, in 157 theory, might be legitimately generated. 159 5. Updating RFC 2460 161 All IPv6 packets MUST contain the entire IPv6 header chain within the 162 first "assumed Path-MTU" bytes of the packet. If a packet is 163 fragmented, the first fragment of the packet (i.e., that with a 164 Fragment Offset of 0) must contain the entire IPv6 header chain 165 within the first "assumed Path-MTU" [RFC1981] [RFC4821] bytes of the 166 packet. 168 Nodes that do not implement Path-MTU Discovery [RFC1981] [RFC4821] 169 must assume a Path-MTU of 1280 bytes (the minimum IPv6 MTU). 171 6. IANA Considerations 173 There are no IANA registries within this document. The RFC-Editor 174 can remove this section before publication of this document as an 175 RFC. 177 7. Security Considerations 179 This document describes the interoperability and security 180 implications of IPv6 packets or first-fragments that fail to include 181 the entire IPv6 header chain. The security implications include the 182 possibility of an attacker evading network security controls such as 183 firewalls and Network Intrusion Detection Systems (NIDS) [CPNI-IPv6]. 185 This document updates RFC 2460 such that those packets are forbidden, 186 thus preventing the aforementioned issues. 188 8. Acknowledgements 190 The authors would like to thank (in alphabetical order) Dave Thaler 191 for providing valuable comments on earlier versions of this document. 193 9. References 195 9.1. Normative References 197 [RFC1981] McCann, J., Deering, S., and J. Mogul, "Path MTU Discovery 198 for IP version 6", RFC 1981, August 1996. 200 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 201 Requirement Levels", BCP 14, RFC 2119, March 1997. 203 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 204 (IPv6) Specification", RFC 2460, December 1998. 206 [RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU 207 Discovery", RFC 4821, March 2007. 209 9.2. Informative References 211 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 212 NAT64: Network Address and Protocol Translation from IPv6 213 Clients to IPv4 Servers", RFC 6146, April 2011. 215 [CPNI-IPv6] 216 Gont, F., "Security Assessment of the Internet Protocol 217 version 6 (IPv6)", UK Centre for the Protection of 218 National Infrastructure, (available on request). 220 Appendix A. Changes from previous versions of the document (to be 221 removed by the RFC Editor before publication of this 222 document as a RFC 224 A.1. Changes from draft-gont-6man-oversized-header-chain-00 226 o The I-D now requires all packets to contain the entire IPv6 header 227 chain within the first "assumed Path-MTU" bytes of the packet 228 (rather than "within the first 1280 bytes of the packet", as 229 required by version -00 of this document). 231 A.2. Changes from draft-manral-6man-tiny-fragments-issues-00 233 o The I-D was largely re-written. 235 o The current I-D notes that the problem lies in packets (or first- 236 fragments) missing the entire IPv6 header chain, rather than on 237 the (small) size of the fragments. 239 Authors' Addresses 241 Fernando Gont 242 SI6 Networks / UTN-FRH 243 Evaristo Carriego 2644 244 Haedo, Provincia de Buenos Aires 1706 245 Argentina 247 Phone: +54 11 4650 8472 248 Email: fgont@si6networks.com 249 URI: http://www.si6networks.com 251 Vishwas Manral 252 Hewlett-Packard Corp. 253 191111 Pruneridge Ave. 254 Cupertino, CA 95014 255 US 257 Phone: 408-447-1497 258 Email: vishwas.manral@hp.com 259 URI: