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Checking references for intended status: Informational ---------------------------------------------------------------------------- == Unused Reference: 'RFC4107' is defined on line 517, but no explicit reference was found in the text == Outdated reference: A later version (-10) exists of draft-ietf-karp-crypto-key-table-04 == Outdated reference: A later version (-16) exists of draft-yeung-g-ikev2-05 -- Obsolete informational reference (is this intentional?): RFC 6822 (Obsoleted by RFC 8202) Summary: 0 errors (**), 0 flaws (~~), 4 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Working Group U. Chunduri 3 Internet-Draft A. Tian 4 Intended status: Informational W. Lu 5 Expires: July 20, 2013 Ericsson Inc., 6 January 16, 2013 8 KARP IS-IS security gap analysis 9 draft-chunduri-karp-is-is-gap-analysis-04 11 Abstract 13 This document analyzes the threats applicable for Intermediate system 14 to Intermediate system (IS-IS) routing protocol and security gaps 15 according to the KARP Design Guide. This document also provides 16 specific requirements to address the gaps with both manual and auto 17 key management protocols. 19 Status of this Memo 21 This Internet-Draft is submitted in full conformance with the 22 provisions of BCP 78 and BCP 79. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF). Note that other groups may also distribute 26 working documents as Internet-Drafts. The list of current Internet- 27 Drafts is at http://datatracker.ietf.org/drafts/current/. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 This Internet-Draft will expire on July 20, 2013. 36 Copyright Notice 38 Copyright (c) 2013 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents 43 (http://trustee.ietf.org/license-info) in effect on the date of 44 publication of this document. Please review these documents 45 carefully, as they describe your rights and restrictions with respect 46 to this document. Code Components extracted from this document must 47 include Simplified BSD License text as described in Section 4.e of 48 the Trust Legal Provisions and are provided without warranty as 49 described in the Simplified BSD License. 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 54 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 55 1.2. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . 3 56 2. Current State . . . . . . . . . . . . . . . . . . . . . . . . 4 57 2.1. Key Usage . . . . . . . . . . . . . . . . . . . . . . . . 4 58 2.1.1. Sub network Independent . . . . . . . . . . . . . . . 4 59 2.1.2. Sub network dependent . . . . . . . . . . . . . . . . 5 60 2.2. Key Agility . . . . . . . . . . . . . . . . . . . . . . . 5 61 2.3. Security Issues . . . . . . . . . . . . . . . . . . . . . 5 62 2.3.1. Replay Attacks . . . . . . . . . . . . . . . . . . . . 6 63 2.3.1.1. Current Recovery mechanism for LSPs . . . . . . . 7 64 2.3.2. Spoofing Attacks . . . . . . . . . . . . . . . . . . . 7 65 2.3.3. DoS Attacks . . . . . . . . . . . . . . . . . . . . . 8 66 3. Gap Analysis and Security Requirements . . . . . . . . . . . . 8 67 3.1. Manual Key Management . . . . . . . . . . . . . . . . . . 8 68 3.2. Key Management Protocols . . . . . . . . . . . . . . . . . 10 69 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 70 5. Security Considerations . . . . . . . . . . . . . . . . . . . 10 71 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11 72 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 73 7.1. Normative References . . . . . . . . . . . . . . . . . . . 11 74 7.2. Informative References . . . . . . . . . . . . . . . . . . 11 75 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12 77 1. Introduction 79 This document analyzes the current state of Intermediate system to 80 Intermediate system (IS-IS) protocol according to the requirements 81 set forth in [RFC6518] for both manual and key management protocols. 83 With currently published work, IS-IS meets some of the requirements 84 expected from a manually keyed routing protocol. Integrity 85 protection is expanded with more cryptographic algorithms and also 86 limited algorithm agility (HMAC-SHA family) is provided with 87 [RFC5310]. Basic form of Intra-connection re-keying capability is 88 provided by the specification [RFC5310] with some gaps as explained 89 in Section 3. 91 This draft summarizes the current state of cryptographic key usage in 92 IS-IS protocol and several previous efforts to analyze IS-IS 93 security. This includes base IS-IS specification [RFC1195], 94 [RFC5304], [RFC5310] and the OPSEC working group document [RFC6039]. 95 Authors would like to acknowledge all the previous work done in the 96 above documents. 98 This document also analyzes applicability of various threats as 99 described in [ietf-karp-threats-reqs] to IS-IS, lists gaps and 100 provides specific recommendations to thwart the applicable threats 101 for both manual keying and for auto key management mechanisms. 103 1.1. Requirements Language 105 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 106 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 107 document are to be interpreted as described in RFC 2119 [RFC2119]. 109 1.2. Acronyms 111 IGP - Interior Gateway Protocol. 113 IIH - IS-IS HELLO PDU. 115 IPv4 - Internet Protocol version 4. 117 KMP - Key Management Protocol (auto key management). 119 LSP - IS-IS Link State PDU. 121 MKM - Manual Key management Protocols. 123 NONCE - Number Once. 125 SA - Security Association. 127 SNP - Sequence number PDU. 129 2. Current State 131 IS-IS is specified in International Standards Organization (ISO) 132 10589, with extensions to support Internet Protocol version 4 (IPv4) 133 described in [RFC1195]. The specification includes an authentication 134 mechanism that allows for any authentication algorithm and also 135 specifies the algorithm for clear text passwords. Further [RFC5304] 136 extends the authentication mechanism to work with HMAC-MD5 and also 137 modifies the base protocol for more effectiveness. [RFC5310] 138 provides algorithm agility, with new generic crypto authentication 139 mechanism (CRYPTO_AUTH) for IS-IS. The CRYPTO_AUTH also introduces 140 Key ID mechanism that map to unique IS-IS Security Associations 141 (SAs). 143 The following sections describe the current authentication key usage 144 for various IS-IS messages, current key change methodologies and the 145 various potential security threats. 147 2.1. Key Usage 149 IS-IS can be provisioned with a per interface, peer-to-peer key for 150 IS-IS HELLO PDUs (IIH) and a group key for Link State PDUs (LSPs) and 151 Sequence number PDUs (SNPs). If provisioned, IIH packets potentially 152 can use the same group key used for LSPs and SNPs. 154 2.1.1. Sub network Independent 156 Link State PDUs, Complete and partial Sequence Number PDUs come under 157 Sub network Independent messages. For protecting Level-1 SNPs and 158 Level-1 LSPs, provisioned Area Authentication key is used. Level-2 159 SNPs as well as Level-2 LSPs use the provisioned domain 160 authentication key. 162 Since authentication is performed on the LSPs transmitted by an IS, 163 rather than on the LSP packets transmitted to a specific neighbor, it 164 is implied that all the ISes within a single flooding domain must be 165 configured with the same key in order for authentication to work 166 correctly. This is also true for SNP packets, though they are 167 limited to link local scope in broadcast networks. 169 If multiple instances share the circuits as specified in [RFC6822], 170 instance specific authentication credentials can be used to protect 171 the LSPs and SNPs with in an area or domain. It is important to 172 note, [RFC6822] also allows usage of topology specific authentication 173 credentials with in an instance for the LSPs and SNPs. 175 2.1.2. Sub network dependent 177 IS-IS HELLO PDUs use the Link Level Authentication key, which may be 178 different from that of LSPs and SNPs. This could be particularly 179 true for point-to-point links. In broadcast networks it is possible 180 to provision the same common key used for LSPs and SNPs, to protect 181 IIH messages. This allows neighbor discovery and adjacency formation 182 with more than one neighbor on the same physical interface. If 183 multiple instances share the circuits as specified in [RFC6822], 184 instance specific authentication credentials can be used to protect 185 Hello messages. 187 2.2. Key Agility 189 Key roll over without effecting the routing protocols operation in 190 general and IS-IS in particular, is necessary for effective key 191 management protocol integration. 193 Current HMAC-MD5 crypto authentication as defined in [RFC5304], 194 suggests a transition mode, so that ISes use a set of keys when 195 verifying the authentication value, to allow key changes. This 196 approach will allow changing the authentication key manually without 197 bringing down the adjacency and without dropping any control packet. 198 But, this can increase the load on control plane for the key 199 transition duration as each control packet may have to be verified by 200 more than one key and also allows to mount a potential Denial of 201 Service (DoS) attack in the transition duration. 203 The above situation is improved with the introduction of Key ID 204 mechanism as defined in [RFC5310]. With this, the receiver 205 determines the active security association (SA) by looking at the Key 206 ID field in the incoming PDU and need not try with other keys, when 207 the integrity check or digest verification fails. But, neither Key 208 co-ordination across the group nor exact key change mechanism is 209 clearly defined. [RFC5310] says: " Normally, an implementation would 210 allow the network operator to configure a set of keys in a key chain, 211 with each key in the chain having a fixed lifetime. The actual 212 operation of these mechanisms is outside the scope of this document." 214 2.3. Security Issues 216 The following section analyzes various security threats possible, in 217 the current state for IS-IS protocol. 219 2.3.1. Replay Attacks 221 Replaying a captured protocol packet to cause damage is a common 222 threat for any protocol. Securing the packet with cryptographic 223 authentication information alone can not mitigate this threat 224 completely. Though this problem is more prevalent in broadcast 225 networks it is important to note, most of the IGP deployments use 226 P2P-over-lan [RFC5309], which makes an adversary replay 'easier' than 227 the traditional P2P networks 229 In intra-session replay attacks a secured protocol packet of the 230 current session is replayed, can cause damage, if there is no other 231 mechanism to confirm this is a replay packet. In inter-session 232 replay attacks, captured packet from one of the previous session can 233 be replayed to cause the damage. IS-IS packets are vulnerable to 234 both these attacks, as there is no sequence number verification for 235 IIH packets and SNP packets. Also with current manual key management 236 periodic key changes across the group are done rarely. Thus the 237 intra-connection and inter-connection replay requirements are not 238 met. 240 IS-IS specifies the use of the HMAC-MD5 [RFC5304] and HMAC-SHA-1 241 family in [RFC5310], to protect IS-IS packets. An adversary could 242 replay old IIHs or replay old SNPs that would cause churn in the 243 network or bring down the adjacencies. 245 1. At the time of adjacency bring up an IS sends IIH packet with 246 empty neighbor list (TLV 6) and with the authentication 247 information as per provisioned authentication mechanism. If this 248 packet is replayed later on the broadcast network, all ISes in 249 the broadcast network can bounce the adjacency to create a huge 250 churn in the network. 252 2. Today LSPs have intra-session replay protection as LSP header 253 contains 32-bit sequence number which is verified for every 254 received packet against the local LSP database. But, if a node 255 in the network is out of service (is undergoing some sort of high 256 availability condition, or an upgrade) for more than LSP refresh 257 time and the rest of the network ages out the LSPs of the node 258 under consideration, an adversary can potentially plunge in 259 inter-session replay attacks in the network. If the key is not 260 changed in the above circumstances, attack can be launched by 261 replaying a old LSP with higher sequence number and fewer 262 prefixes or fewer adjacencies. This may force the receiver to 263 accept and remove the routes from the routing table, which 264 eventually causes traffic disruption to those prefixes. However, 265 as per the IS-IS specification there is a built-in recovery 266 mechanism for LSPs from inter-session replay attacks and it is 267 further discussed in Section 2.3.1.1. 269 3. In any IS-IS network (broadcast or otherwise), if a old and an 270 empty Complete Sequence Number packet (CSNP) is replayed this can 271 cause LSP flood in the network. Similarly a replayed Partial 272 Sequence Number packet (PSNP) can cause LSP flood in the 273 broadcast network. 275 2.3.1.1. Current Recovery mechanism for LSPs 277 In the event of inter-session replay attack by an adversary, as LSP 278 with higher sequence number gets accepted, it also gets propagated 279 until it reaches the originating node of the LSP. The originator 280 recognizes the LSP is "newer" than in the local database and this 281 prompts the originator to flood a newer version of the LSP with 282 higher sequence number than the received. This newer version can 283 potentially replace any versions of the replayed LSP which may exist 284 in the network. 286 But in the above process, depending on where in the network the 287 replay is initiated, how quick the nodes in the network react to the 288 replayed LSP and also how different the content in the accepted LSP 289 determines the damage caused by the replayed LSP. 291 2.3.2. Spoofing Attacks 293 IS-IS shares the same key between all neighbors in an area or in a 294 domain to protect the LSP, SNP packets and in broadcast networks even 295 IIH packets. False advertisement by a router is not within scope of 296 the KARP work. However, given the wide sharing of keys as described 297 above, there is a significant risk that an attacker can compromise a 298 key from one device, and use it to falsely participate in the 299 routing, possibly even in a very separate part of the network. 301 If the same underlying topology is shared across multiple instances 302 to transport routing/application information as defined in [RFC6822], 303 it is necessary to use different authentication credentials for 304 different instances. In this connection, based on the deployment 305 considerations, if certain topologies in a particular IS-IS instance 306 require more protection from spoofing attacks and less exposure, 307 topology specific authentication credentials can be used for LSPs and 308 SNPs as facilitated in [RFC6822]. 310 Currently possession of the key it self is used as authentication 311 check and there is no identity check done separately. Spoofing 312 occurs when an illegitimate device assumes the identity of a 313 legitimate one. An attacker can use spoofing as a means for 314 launching various types of attacks. For example: 316 1. The attacker can send out unrealistic routing information that 317 might cause the disruption of network services such as block 318 holes. 320 2. A rogue system having access to the common key used to protect 321 the LSP, can send an LSP, setting the Remaining Lifetime field to 322 zero, and flooding it thereby initiating a purge. Subsequently, 323 this also can cause the sequence number of all the LSPs to 324 increase quickly to max out the sequence number space, which can 325 cause an IS to shut down for MaxAge + ZeroAgeLifetime period to 326 allow the old LSPs to age out in other ISes of the same flooding 327 domain. 329 2.3.3. DoS Attacks 331 Denial-of-service (DoS) attacks using the authentication mechanism is 332 possible and an attacker can send packets which can overwhelm the 333 security mechanism itself. An example is initiating an overwhelming 334 load of spoofed but integrity protected protocol packets, so that the 335 receiver needs to process the integrity check, only to discard the 336 packet. This can cause significant CPU usage. DoS attacks are not 337 generally preventable with in the routing protocol. As the attackers 338 are often remote, the DoS attacks are more damaging to area-scoped or 339 domain-scoped packet receivers than link-local scoped packet 340 receivers. 342 3. Gap Analysis and Security Requirements 344 This section outlines the differences between the current state of 345 the IS-IS routing protocol and the desired state as specified in KARP 346 Design Guidelines [RFC6518]. The section focuses on where IS-IS 347 protocol fails to meet general requirements as specified in the 348 threats and requirements document. 350 This section also describes security requirements that should be met 351 by IS-IS implementations that are secured by manual as well as auto 352 key management protocols. 354 3.1. Manual Key Management 356 1. With CRYPTO_AUTH specification [RFC5310], IS-IS packets can be 357 protected with HMAC-SHA family of cryptographic algorithms. The 358 specification provides the limited algorithm agility (SHA 359 family). By using Key IDs, it also conceals the algorithm 360 information from the protected control messages. 362 2. Even though both intra and inter session replay attacks are best 363 prevented by deploying key management protocols with frequent key 364 change capability, basic constructs for sequence number should be 365 there in the protocol messages. So, some basic or extended 366 sequence number mechanism should be in place to protect IIH 367 packets and SNP packets. The sequence number should be increased 368 for each protocol packet. This allows mitigation of some of the 369 replay threats as mentioned in Section 2.3.1. 371 3. Any common key mechanism with keys shared across a group of 372 routers is susceptible to spoofing attacks caused by a malicious 373 router. Separate authentication check (apart from the integrity 374 check to verify the digest) with digital signatures as described 375 in [RFC2154], can effectively nullify this attack. But this 376 approach was never deployed and one can only assume due to 377 operational considerations at that time. The alternative 378 approach to thwart this threat would be by using the keys from 379 the group key management protocol. As the group key(s) are 380 generated by authenticating the member ISes in the group first, 381 and then periodically rekeyed, per packet identity or 382 authentication check may not be needed. 384 4. In general DoS attacks may not be preventable with mechanism from 385 routing protocols itself. But some form of Admin controlled 386 lists (ACLs) at the forwarding plane can reduce the damage. 387 There are some other forms the DoS attacks common to any protocol 388 are not in scope as per the section 2.2 in [I-D.ietf-karp- 389 threats-reqs]. 391 As discussed in Section 2.2, though Key ID mechanism in [RFC5310] 392 helps, better key co-ordination mechanism for key roll over is 393 desirable even with manual key management. But, it fell short of 394 specifying exact mechanism other than using key chains. The specific 395 requirements: 397 a. Keys SHOULD be able to change without affecting the established 398 adjacency and even better without any control packet loss. 400 b. Keys SHOULD be able to change without effecting the protocol 401 operations, for example, LSP flooding should not be held for a 402 specific Key ID availability. 404 c. Any proposed mechanism SHOULD also be further incrementally 405 deployable with key management protocols. 407 3.2. Key Management Protocols 409 In broadcast deployments, the keys used for protecting IS-IS 410 protocols messages can, in particular, be group keys. A mechanism, 411 similar to as described in [I-D.weis-gdoi-mac-tek] can be used to 412 distribute group keys to a group of ISes in Level-1 area or Level-2 413 domain, using GDOI as specified in [RFC6407]. There are also similar 414 approaches with IKEv2 based group key management solutions, to 415 routing protocols as described in [I-D.yeung-g-ikev2] and 416 [I-D.hartman-karp-mrkmp]. 418 If a group key is used, the authentication granularity becomes group 419 membership of devices, not peer authentication between devices. 420 Group key management protocol deployed SHOULD be capable of 421 supporting rekeying support. 423 In some deployments, where IS-IS point-to-point (P2P) mode is used 424 for adjacency bring-up, sub network dependent messages (IIHs) can use 425 a different key shared between the two point-to-point peers, while 426 all other messages use a group key. When group keying mechanism is 427 deployed, even the P2P IIHs can be protected with the common group 428 keys. This approach facilitates one key management mechanism instead 429 of both pair-wise keying and group keying protocols to be deployed 430 together. If same circuits are shared across multiple instances, the 431 granularity of the group can become per instance for IIHs and per 432 instance/topology for LSPs and SNPs as specified in the [RFC6822]. 434 Effective key change capability with in the routing protocol which 435 allows key roll over without impacting the routing protocol 436 operation, is one of the requirements for deploying any group key 437 mechanism. Once such mechanism is in place with deployment of group 438 key management protocol, IS-IS can be protected from various threats 439 not limited to intra and inter session replay attacks and spoofing 440 attacks. 442 Specific use of crypto tables [I-D.ietf-karp-crypto-key-table] should 443 be defined for IS-IS protocol. 445 4. IANA Considerations 447 This document defines no new namespaces. 449 5. Security Considerations 451 This document is mostly about security considerations of IS-IS 452 protocol, lists potential threats and security requirements for 453 solving those threats. This document does not introduce any new 454 security threats for IS-IS protocol. For more detailed security 455 considerations please refer the Security Considerations section of 456 the KARP Design Guide [RFC6518] document as well as KARP threat 457 document [I-D.ietf-karp-threats-reqs] 459 6. Acknowledgements 461 Authors would like to thank Joel Halpern for initial discussions on 462 this document and giving valuable review comments. Authors would 463 like to acknowledge Naiming Shen for reviewing and providing feedback 464 on this document. 466 7. References 468 7.1. Normative References 470 [RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and 471 dual environments", RFC 1195, December 1990. 473 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 474 Requirement Levels", BCP 14, RFC 2119, March 1997. 476 [RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic 477 Authentication", RFC 5304, October 2008. 479 [RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R., 480 and M. Fanto, "IS-IS Generic Cryptographic 481 Authentication", RFC 5310, February 2009. 483 7.2. Informative References 485 [I-D.hartman-karp-mrkmp] 486 Hartman, S., Zhang, D., and G. Lebovitz, "Multicast Router 487 Key Management Protocol (MaRK)", 488 draft-hartman-karp-mrkmp-05 (work in progress), 489 September 2012. 491 [I-D.ietf-karp-crypto-key-table] 492 Housley, R., Polk, T., Hartman, S., and D. Zhang, 493 "Database of Long-Lived Symmetric Cryptographic Keys", 494 draft-ietf-karp-crypto-key-table-04 (work in progress), 495 October 2012. 497 [I-D.ietf-karp-threats-reqs] 498 Lebovitz, G., Bhatia, M., and B. Weis, "Keying and 499 Authentication for Routing Protocols (KARP) Overview, 500 Threats, and Requirements", 501 draft-ietf-karp-threats-reqs-07 (work in progress), 502 December 2012. 504 [I-D.weis-gdoi-mac-tek] 505 Weis, B. and S. Rowles, "GDOI Generic Message 506 Authentication Code Policy", draft-weis-gdoi-mac-tek-03 507 (work in progress), September 2011. 509 [I-D.yeung-g-ikev2] 510 Rowles, S., Yeung, A., Tran, P., and Y. Nir, "Group Key 511 Management using IKEv2", draft-yeung-g-ikev2-05 (work in 512 progress), October 2012. 514 [RFC2154] Murphy, S., Badger, M., and B. Wellington, "OSPF with 515 Digital Signatures", RFC 2154, June 1997. 517 [RFC4107] Bellovin, S. and R. Housley, "Guidelines for Cryptographic 518 Key Management", BCP 107, RFC 4107, June 2005. 520 [RFC5309] Shen, N. and A. Zinin, "Point-to-Point Operation over LAN 521 in Link State Routing Protocols", RFC 5309, October 2008. 523 [RFC6039] Manral, V., Bhatia, M., Jaeggli, J., and R. White, "Issues 524 with Existing Cryptographic Protection Methods for Routing 525 Protocols", RFC 6039, October 2010. 527 [RFC6407] Weis, B., Rowles, S., and T. Hardjono, "The Group Domain 528 of Interpretation", RFC 6407, October 2011. 530 [RFC6518] Lebovitz, G. and M. Bhatia, "Keying and Authentication for 531 Routing Protocols (KARP) Design Guidelines", RFC 6518, 532 February 2012. 534 [RFC6822] Previdi, S., Ginsberg, L., Shand, M., Roy, A., and D. 535 Ward, "IS-IS Multi-Instance", RFC 6822, December 2012. 537 Authors' Addresses 539 Uma Chunduri 540 Ericsson Inc., 541 300 Holger Way, 542 San Jose, California 95134 543 USA 545 Phone: 408 750-5678 546 Email: uma.chunduri@ericsson.com 548 Albert Tian 549 Ericsson Inc., 550 300 Holger Way, 551 San Jose, California 95134 552 USA 554 Phone: 408 750-5210 555 Email: albert.tian@ericsson.com 557 Wenhu Lu 558 Ericsson Inc., 559 300 Holger Way, 560 San Jose, California 95134 561 USA 563 Email: wenhu.lu@ericsson.com