idnits 2.17.1 draft-ietf-6man-nd-extension-headers-00.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- ** The document seems to lack an IANA Considerations section. (See Section 2.2 of https://www.ietf.org/id-info/checklist for how to handle the case when there are no actions for IANA.) -- The draft header indicates that this document updates RFC3971, but the abstract doesn't seem to mention this, which it should. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year (Using the creation date from RFC3971, updated by this document, for RFC5378 checks: 2003-10-17) -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. If you have contacted all the original authors and they are all willing to grant the BCP78 rights to the IETF Trust, then this is fine, and you can ignore this comment. If not, you may need to add the pre-RFC5378 disclaimer. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (June 29, 2012) is 4316 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-07) exists of draft-ietf-v6ops-ra-guard-implementation-04 Summary: 1 error (**), 0 flaws (~~), 2 warnings (==), 3 comments (--).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 UK CPNI 4 Updates: 3971, 4861 (if approved) June 29, 2012 5 Intended status: Standards Track 6 Expires: December 31, 2012 8 Security Implications of the Use of IPv6 Extension Headers with IPv6 9 Neighbor Discovery 10 draft-ietf-6man-nd-extension-headers-00 12 Abstract 14 This document analyzes the security implications of using IPv6 15 Extension Headers with Neighbor Discovery (ND) messages. It updates 16 RFC 4861 such that use of the IPv6 Fragmentation Header is forbidden 17 in all Neighbor Discovery messages, thus allowing for simple and 18 effective counter-measures for Neighbor Discovery attacks. Finally, 19 it discusses the security implications of using IPv6 fragmentation 20 with SEcure Neighbor Discovery (SEND), and provides advice such that 21 the aforementioned security implications are mitigated. 23 Status of this Memo 25 This Internet-Draft is submitted in full conformance with the 26 provisions of BCP 78 and BCP 79. 28 Internet-Drafts are working documents of the Internet Engineering 29 Task Force (IETF). Note that other groups may also distribute 30 working documents as Internet-Drafts. The list of current Internet- 31 Drafts is at http://datatracker.ietf.org/drafts/current/. 33 Internet-Drafts are draft documents valid for a maximum of six months 34 and may be updated, replaced, or obsoleted by other documents at any 35 time. It is inappropriate to use Internet-Drafts as reference 36 material or to cite them other than as "work in progress." 38 This Internet-Draft will expire on December 31, 2012. 40 Copyright Notice 42 Copyright (c) 2012 IETF Trust and the persons identified as the 43 document authors. All rights reserved. 45 This document is subject to BCP 78 and the IETF Trust's Legal 46 Provisions Relating to IETF Documents 47 (http://trustee.ietf.org/license-info) in effect on the date of 48 publication of this document. Please review these documents 49 carefully, as they describe your rights and restrictions with respect 50 to this document. Code Components extracted from this document must 51 include Simplified BSD License text as described in Section 4.e of 52 the Trust Legal Provisions and are provided without warranty as 53 described in the Simplified BSD License. 55 Table of Contents 57 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 58 2. Traditional Neighbor Discovery and IPv6 Fragmentation . . . . 5 59 3. SEcure Neighbor Discovery (SEND) and IPv6 Fragmentation . . . 6 60 4. Specification . . . . . . . . . . . . . . . . . . . . . . . . 7 61 5. Security Considerations . . . . . . . . . . . . . . . . . . . 8 62 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9 63 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10 64 7.1. Normative References . . . . . . . . . . . . . . . . . . . 10 65 7.2. Informative References . . . . . . . . . . . . . . . . . . 10 66 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 12 68 1. Introduction 70 The Neighbor Discovery Protocol (NDP) is specified in RFC 4861 71 [RFC4861] and RFC 4862 [RFC4862]. It is used by both hosts and 72 routers. Its functions include Neighbor Discovery (ND), Router 73 Discovery (RD), Address Autoconfiguration, Address Resolution, 74 Neighbor Unreachability Detection (NUD), Duplicate Address Detection 75 (DAD), and Redirection. 77 Many of the possible attacks against the Neighbor Discovery Protocol 78 are discussed in detail in [RFC3756]. In order to mitigate the 79 aforementioned possible attacks, the SEcure Neighbor Discovery (SEND) 80 was standardized. SEND employs a number of mechanisms to certify the 81 origin of Neighbor Discovery packets and the authority of routers, 82 and to protect Neighbor Discovery packets from being the subject of 83 modification or replay attacks. 85 However, a number of factors, such as the use of trust anchors and 86 the unavailability of SEND implementations for many widely-deployed 87 operating systems, make SEND hard to deploy [Gont-DEEPSEC2011]. 88 Thus, in many general scenarios it may be necessary and/or convenient 89 to use other mitigation techniques for NDP-based attacks. The 90 following "lightweight" mitigations are currently available for NDP 91 attacks: 93 o Layer-2 filtering of Neighbor Discovery packets (such as RA-Guard 94 [RFC6105]) 96 o Neighbor Discovery monitoring tools (e.g., such as NDPMon 97 [NDPMon]) 99 IPv6 Router Advertisement Guard (RA-Guard) is a mitigation technique 100 for attack vectors based on ICMPv6 Router Advertisement messages. It 101 is meant to block attack packets at a layer-2 device before the 102 attack packets actually reach the target nodes. [RFC6104] describes 103 the problem statement of "Rogue IPv6 Router Advertisements", and 104 [RFC6105] specifies the "IPv6 Router Advertisement Guard" 105 functionality. 107 Tools such as NDPMon [NDPMon] and ramond [ramond] aim at monitoring 108 Neighbor Discovery traffic in the hopes of detecting possible attacks 109 when there are discrepancies between the information advertised in 110 Neighbor Discovery packets and the information stored on a local 111 database. 113 A key challenge that these mitigation or monitoring techniques face 114 is that introduced by IPv6 fragmentation, since it is trivial for an 115 attacker to conceal his attack by fragmenting his packets into 116 multiple fragments. This may limit or even eliminate the 117 effectiveness of the aforementioned mitigation or monitoring 118 techniques. Recent work [CPNI-IPv6] indicates that current 119 implementations of the aforementioned "lightweight" mitigations for 120 NDP attacks can be trivially evaded. For example, as noted in 121 [I-D.ietf-v6ops-ra-guard-implementation], current RA-Guard 122 implementations can be trivially evaded by fragmenting the attack 123 packets into multiple fragments, such that the layer-2 device cannot 124 find all the necessary information to perform packet filtering in the 125 same packet. While Neighbor Discovery monitoring tools could (in 126 theory implement IPv6 fragment reassembly, this is usually an arms- 127 race with the attacker (an attacker generate lots of forged fragments 128 to "confuse" the monitoring tools), and therefore the aforementioned 129 tools are unreliable for the detection of such attacks. 131 Section 2 analyzes the use of IPv6 fragmentation in traditional 132 Neighbor discovery. Section 3 analyzes the use of IPv6 fragmentation 133 in SEcure Neighbor Discovery (SEND). Section 4 formally updates RFC 134 4861 such that use of the IPv6 Fragment Header with traditional 135 Neighbor Discovery is forbidden, and provides advice on the use of 136 IPv6 fragmentation with SEND. 138 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 139 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 140 document are to be interpreted as described in RFC 2119 [RFC2119]. 142 2. Traditional Neighbor Discovery and IPv6 Fragmentation 144 The only potential use case for IPv6 fragmentation with traditional 145 (i.e., non-SEND) IPv6 Neighbor Discovery would be that in which a 146 Router Advertisement must include a large number of options (Prefix 147 Information Options, Route Information Options, etc.). However, this 148 could still be achieved without employing fragmentation, by splitting 149 the aforementioned information into multiple Router Advertisement 150 messages. 152 Some Neighbor Discovery implementations are known to silently 153 ignore Router Advertisement messages that employ fragmentation. 154 Therefore, splitting the necessary information into multiple RA 155 messages (rather than sending a large RA message that is 156 fragmented into multiple IPv6 fragments) is probably desirable 157 even from an interoperability point of view. 159 As a result of the aforementioned considerations, and since avoiding 160 the use of IPv6 fragmentation in traditional Neighbor Discovery would 161 greatly simplify and improve the effectiveness of monitoring and 162 filtering ND, Section 4 specifies that hosts silently ignore 163 traditional Neighbor Discovery messages (i.e., those specified in 164 [RFC4861]) that employ IPv6 fragmentation. 166 3. SEcure Neighbor Discovery (SEND) and IPv6 Fragmentation 168 SEND packets typically carry more information than traditional 169 Neighbor Discovery packets: for example, they include additional 170 options such as the CGA option and the RSA signature option. 172 In the case of Neighbor Discovery messages specified in [RFC4861], 173 the situation is roughly the same: if more information than would fit 174 in a non-fragmented Neighbor Discovery packet needs to be sent, it 175 should be split into multiple Neighbor Discovery messages (such that 176 IPv6 fragmentation is avoided). 178 However, Certification Path Advertisement messages (specified in 179 [RFC3971]) pose a different situation, since the Certificate Option 180 they include contain much more information than any other Neighbor 181 Discovery option. For example, Appendix C of [RFC3971] reports 182 Certification Path Advertisement messages from 1050 to 1066 bytes on 183 an Ethernet link layer. Since the size of CPA messages could 184 potentially exceed the MTU of the local link, we recommend that 185 fragmented CPA messages be normally processed (although *sending* 186 fragmented CPA messages is discouraged). 188 It should be noted that relying on fragmentation opens the door to a 189 variety of IPv6 fragmentation-based attacks. In particular, if an 190 attacker is located on the same broadcast domain as the victim host, 191 and Certification Path Advertisement messages employ IPv6 192 fragmentation, it would be trivial for the attacker to forge IPv6 193 fragment such that they result in "Fragment ID collisions", causing 194 both the attack fragments and the legitimate fragments to be 195 discarded by the victim node. This would eventually cause the 196 Authorization Delegation Discovery to fail, thus leading the host to 197 fall back (depending to local configuration) either to unsecured 198 mode, or to reject the corresponding Router Advertisement messages 199 (possibly resulting in a Denial of Service). 201 4. Specification 203 Nodes MUST NOT employ IPv6 fragmentation for sending any of the 204 following Neighbor Discovery and SEcure Neighbor Discovery messages: 205 Neighbor Solicitation, Neighbor Advertisement, Router Solicitation, 206 Router Advertisement, Redirect, and Certification Path Solicitation. 207 SEND nodes SHOULD NOT employ IPv6 fragmentation for sending 208 Certification Path Advertisement messages. 210 Nodes MUST silently ignore the following Neighbor Discovery and 211 SEcure Neighbor Discovery messages if the packets carrying them 212 include an IPv6 Fragmentation Header: Neighbor Solicitation, Neighbor 213 Advertisement, Router Solicitation, Router Advertisement, Redirect, 214 and Certification Path Solicitation. 216 Nodes SHOULD normally process Certification Path Advertisement 217 messages that employ IPv6 fragmentation. 219 5. Security Considerations 221 The IPv6 Fragmentation Header can be leveraged to circumvent network 222 monitoring tools and current implementations of mechanisms such as 223 RA-Guard [I-D.ietf-v6ops-ra-guard-implementation]. By updating the 224 relevant specifications such that the IPv6 Fragment Header is not 225 allowed in any Neighbor Discovery messages except "Certification Path 226 Advertisement", protection of local nodes against Neighbor Discovery 227 attacks, and monitoring of Neighbor Discovery traffic is greatly 228 simplified. 230 [I-D.ietf-v6ops-ra-guard-implementation] discusses an improvement to 231 the RA-Guard mechanism that can mitigate Neighbor Discovery attacks 232 that employ IPv6 Fragmentation. However, it should be noted that 233 unless [RFC4861] is updated (as proposed in this document), Neighbor 234 Discovery monitoring tools (such as NDPMon [NDPMon]) would remain 235 unreliable and trivial to circumvent by a skilled attacker. 237 As noted in Section 3, use of SEND could potentially result in 238 fragmented "Certification Path Advertisement" messages, thus allowing 239 an attacker to employ IPv6 fragmentation-based attacks against such 240 messages. Therefore, to the extent that is possible, such use of 241 fragmentation should be avoided. 243 6. Acknowledgements 245 The author would like to thank (in alphabetical order) Mikael 246 Abrahamsson, Ran Atkinson, Ron Bonica, Jean-Michel Combes, David 247 Farmer, Roque Gagliano, Bob Hinden, Philip Homburg, Ray Hunter, 248 Arturo Servin, and Mark Smith, for providing valuable comments on 249 earlier versions of this document. 251 This document resulted from the project "Security Assessment of the 252 Internet Protocol version 6 (IPv6)" [CPNI-IPv6], carried out by 253 Fernando Gont on behalf of the UK Centre for the Protection of 254 National Infrastructure (CPNI). The author would like to thank the 255 UK CPNI, for their continued support. 257 7. References 259 7.1. Normative References 261 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 262 Requirement Levels", BCP 14, RFC 2119, March 1997. 264 [RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure 265 Neighbor Discovery (SEND)", RFC 3971, March 2005. 267 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 268 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 269 September 2007. 271 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 272 Address Autoconfiguration", RFC 4862, September 2007. 274 7.2. Informative References 276 [RFC3756] Nikander, P., Kempf, J., and E. Nordmark, "IPv6 Neighbor 277 Discovery (ND) Trust Models and Threats", RFC 3756, 278 May 2004. 280 [RFC6104] Chown, T. and S. Venaas, "Rogue IPv6 Router Advertisement 281 Problem Statement", RFC 6104, February 2011. 283 [RFC6105] Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and J. 284 Mohacsi, "IPv6 Router Advertisement Guard", RFC 6105, 285 February 2011. 287 [NDPMon] "NDPMon - IPv6 Neighbor Discovery Protocol Monitor", 288 . 290 [ramond] "ramond", . 292 [I-D.ietf-v6ops-ra-guard-implementation] 293 Gont, F., "Implementation Advice for IPv6 Router 294 Advertisement Guard (RA-Guard)", 295 draft-ietf-v6ops-ra-guard-implementation-04 (work in 296 progress), May 2012. 298 [CPNI-IPv6] 299 Gont, F., "Security Assessment of the Internet Protocol 300 version 6 (IPv6)", UK Centre for the Protection of 301 National Infrastructure, (available on request). 303 [Gont-DEEPSEC2011] 304 Gont, "Results of a Security Assessment of the Internet 305 Protocol version 6 (IPv6)", DEEPSEC 2011 Conference, 306 Vienna, Austria, November 2011, . 310 Author's Address 312 Fernando Gont 313 Centre for the Protection of National Infrastructure 315 Email: fernando@gont.com.ar 316 URI: http://www.cpni.gov.uk