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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 MILE N. Cam-Winget, Ed. 3 Internet-Draft S. Appala 4 Intended status: Standards Track S. Pope 5 Expires: September 28, 2019 Cisco Systems 6 P. Saint-Andre 7 Mozilla 8 March 27, 2019 10 Using XMPP for Security Information Exchange 11 draft-ietf-mile-xmpp-grid-11 13 Abstract 15 This document describes how to use the Extensible Messaging and 16 Presence Protocol (XMPP) to collect and distribute security incident 17 reports and other security-relevant information between network- 18 connected devices, primarily for the purpose of communication among 19 Computer Security Incident Response Teams and associated entities. 20 To illustrate the principles involved, this document describes such a 21 usage for the Incident Object Description Exchange Format (IODEF). 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 https://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 September 28, 2019. 40 Copyright Notice 42 Copyright (c) 2019 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 (https://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 . . . . . . . . . . . . . . . . . . . . . . . . 2 58 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 59 3. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 4 60 4. Workflow . . . . . . . . . . . . . . . . . . . . . . . . . . 5 61 5. Service Discovery . . . . . . . . . . . . . . . . . . . . . . 7 62 6. Publish-Subscribe . . . . . . . . . . . . . . . . . . . . . . 9 63 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 64 8. Security Considerations . . . . . . . . . . . . . . . . . . . 12 65 8.1. Trust Model . . . . . . . . . . . . . . . . . . . . . . . 13 66 8.2. Threat Model . . . . . . . . . . . . . . . . . . . . . . 15 67 8.3. Countermeasures . . . . . . . . . . . . . . . . . . . . . 19 68 8.4. Summary . . . . . . . . . . . . . . . . . . . . . . . . . 22 69 9. Privacy Considerations . . . . . . . . . . . . . . . . . . . 23 70 10. Operations and Management Considerations . . . . . . . . . . 23 71 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 24 72 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 24 73 12.1. Normative References . . . . . . . . . . . . . . . . . . 24 74 12.2. Informative References . . . . . . . . . . . . . . . . . 26 75 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26 77 1. Introduction 79 This document defines an architecture, i.e., "XMPP-Grid", as a method 80 for using the Extensible Messaging and Presence Protocol (XMPP) 81 [RFC6120] to collect and distribute security incident reports and 82 other security-relevant information among network platforms, 83 endpoints, and any other network-connected device, primarily for the 84 purpose of communication among Computer Security Incident Response 85 Teams and associated entities. In effect, this document specifies an 86 Applicability Statement ([RFC2026], Section 3.2) that defines how to 87 use XMPP for the exchange of security notifications on a controlled- 88 access network among authorized entities. 90 Among other things, XMPP provides a publish-subscribe service 91 [XEP-0060] that acts as a broker, enabling control-plane functions by 92 which entities can discover available information to be published or 93 consumed. Although such information can take the form of any 94 structured data (XML, JSON, etc.), this document illustrates the 95 principles of XMPP-Grid with examples that use the Incident Object 96 Description Exchange Format (IODEF) [RFC7970]. That is, while other 97 security information formats can be shared using XMPP, this document 98 uses IODEF as one such example format that can be published and 99 consumed using XMPP. 101 2. Terminology 103 This document uses XMPP terminology defined in [RFC6120] and 104 [XEP-0060]. Because the intended audience for this document is those 105 who implement and deploy security reporting systems, mappings are 106 provided for the benefit of XMPP developers and operators. 108 Broker: A specific type of controller containing control plane 109 functions; as used here, the term refers to an XMPP publish- 110 subscribe service. 112 Broker Flow: A method by which security incident reports and other 113 security-relevant information is published and consumed in a 114 mediated fashion through a Broker. In this flow, the Broker 115 handles authorization of Consumers and Providers to Topics, 116 receives messages from Providers, and delivers published messages 117 to Consumers. 119 Consumer: An entity that contains functions to receive information 120 from other components; as used here, the term refers to an XMPP 121 publish-subscribe Subscriber. 123 Controller: A "component containing control plane functions that 124 manage and facilitate information sharing or execute on security 125 functions"; as used here, the term refers to an XMPP server, which 126 provides core message delivery [RFC6120] used by publish-subscribe 127 entities. 129 Node: The XMPP term for a Topic. 131 Platform: Any entity that connects to the XMPP-Grid in order to 132 publish or consume security-relevant information. 134 Provider: An entity that contains functions to provide information 135 to other components; as used here, the term refers to an XMPP 136 publish-subscribe Publisher. 138 Topic: A contextual information channel created on a Broker at which 139 messages generated by a Provider are propagated in real time to 140 one or more Consumers. Each Topic is limited to a specific type 141 and format of security data (e.g. IODEF namespace) and provides 142 an XMPP interface by which the data can be obtained. 144 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 145 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 146 "OPTIONAL" in this document are to be interpreted as described in BCP 147 14 [RFC2119] [RFC8174] when, and only when, they appear in all 148 capitals, as shown here. 150 3. Architecture 152 The following figure illustrates the architecture of XMPP-Grid. 154 +--------------------------------------+ 155 | +--------------------------------------+ 156 | | +--------------------------------------+ 157 | | | | 158 +-| | Platforms | 159 +-| | 160 +--------------------------------------+ 161 / \ / \ / \ 162 / C \ / \ / \ 163 - o - - d - - - 164 ||n||A | a |B | |C 165 ||t|| | t | | | 166 - r - - a - | | 167 \ o / \ / | | 168 \ l / \ / | | 169 /|---------------------|\ | | 170 /|----/ \--------| d |--|\ 171 / / Controller \ ctrl | a | \ 172 \ \ & Broker / plane | t | / 173 \|----\ /--------| a |--|/ 174 \|---------------------|/ | | 175 / \ / \ | | 176 / C \ / \ | | 177 - o - - d - | | 178 ||n||A | a |B | |C 179 ||t|| | t | | | 180 - r - - a - - - 181 \ o / \ / \ / 182 \ l / \ / \ / 183 +------------------------------------+ 184 | |-+ 185 | Platforms | | 186 | | |-+ 187 +------------------------------------+ | | 188 +------------------------------------+ | 189 +------------------------------------+ 191 Figure 1: XMPP-Grid Architecture 193 Platforms connect to the Controller (XMPP server) to authenticate and 194 then establish appropriate authorizations to be a Provider or 195 Consumer of topics of interest at the Broker. The control plane 196 messaging is established through XMPP and shown as "A" (control plane 197 interface) in Figure 1. Authorized Platforms can then share data 198 either through the Broker (shown as "B" in Figure 1) or in some cases 199 directly (shown as "C" in Figure 1). This document focuses primarily 200 on the Broker Flow for information sharing ("direct flow" 201 interactions can be used for specialized purposes such as bulk data 202 transfer, but methods for doing so are outside the scope of this 203 document). 205 4. Workflow 207 Implementations of XMPP-Grid workflow adhere to the following 208 workflow: 210 a. A Platform with a source of security data requests connection to 211 the XMPP-Grid via a Controller. 213 b. The Controller authenticates the Platform. 215 c. The Platform establishes authorized privileges (e.g. privilege to 216 publish and/or subscribe to one or more Topics) with a Broker. 218 d. The Platform can publish security incident reports and other 219 security-relevant information to a Topic, subscribe to a Topic, 220 query a Topic, or any combination of these operations. 222 e. A Provider unicasts its Topic updates to the Grid in real time 223 through a Broker. The Broker handles replication and 224 distribution of the Topic to Consumers. A Provider can publish 225 the same or different data to multiple Topics. 227 f. Any Platform on the Grid can subscribe to any Topics published to 228 the Grid (as permitted by authorization policy), and (as 229 Consumers) will then receive a continual, real-time stream of 230 updates from the Topics to which it is subscribed. 232 The general workflow is summarized in the figure below: 234 +--------------+ +------------+ +---------------+ 235 | IODEF Client | | Controller | | IODEF Service | 236 | (Consumer) | | & Broker | | (Provider) | 237 +--------------+ +------------+ +---------------+ 238 | | | 239 | Establish XMPP | | 240 | Client Session | | 241 | (RFC 6120) | | 242 |--------------------->| | 243 | | Establish XMPP | 244 | | Client Session | 245 | | (RFC 6120) | 246 | |<------------------------| 247 | | Request Topic Creation | 248 | | (XEP-0060) | 249 | |<------------------------| 250 | | Topic Creation Success | 251 | | (XEP-0060) | 252 | |------------------------>| 253 | Request Topic List | | 254 | (XEP-0030) | | 255 |--------------------->| | 256 | Return Topic List | | 257 | (XEP-0030) | | 258 |<---------------------| | 259 | | | 260 | Query Each Topic | | 261 | (XEP-0030) | | 262 |--------------------->| | 263 | Return Topic Data | | 264 | Including Topic Type | | 265 | (XEP-0030) | | 266 |<---------------------| | 267 | | | 268 | Subscribe to IODEF | | 269 | Topic (XEP-0060) | | 270 |--------------------->| | 271 | Subscription Success | | 272 | (XEP-0060) | | 273 |<---------------------| | 274 | | Publish IODEF Incident | 275 | | (XEP-0060) | 276 | Receive IODEF |<------------------------| 277 | Incident (XEP-0060) | | 278 |<---------------------| | 279 | | | 281 Figure 2: IODEF Example Workflow 283 XMPP-Grid implementations MUST adhere to the mandatory-to-implement 284 and mandatory-to-negotiate features as defined in [RFC6120]. 285 Similarly, implementations MUST implement [XEP-0060] to facilitate 286 the asynchronous sharing for information. Implementations SHOULD 287 implement Service Discovery as defined in [XEP-0030] to facilitate 288 the means to dynamically discover the available information and 289 namespaces (Topics) to be published or consumed. Implementations 290 should take caution if their deployments allow for a large number of 291 topics. The Result Set Management as defined in [XEP-0059], SHOULD 292 be used to allow the requesting entity to explicitly request Service 293 Discovery result sets to be returned in pages or limited size, if the 294 discovery results are larger in size. Note that the control plane 295 may optionally also implement [XEP-0203] to facilitate delayed 296 delivery of messages to the connected consumer as described in 297 [XEP-0060]. Since information may be timely and sensitive, 298 capability providers should communicate to the controller whether its 299 messages can be cached for delayed delivery during configuration; 300 such function is out of scope for this document. 302 The following sections provide protocol examples for the service 303 discovery and publish-subscribe parts of the workflow. 305 5. Service Discovery 307 Using the XMPP service discovery extension [XEP-0030], a Controller 308 enables Platforms to discover what information can be consumed 309 through the Broker, and at which Topics. Platforms could use 310 [XEP-0059] to restrict the size of the result sets the Controller 311 returns in Service Discovery response. As an example, the Controller 312 at 'security-grid.example' might provide a Broker at 313 'broker.security-grid.example' hosting a number of Topics. A 314 Platform at 'xmpp-grid-client@mile-host.example' would query the 315 Broker about its available Topics by sending an XMPP "disco#items" 316 request to the Broker: 318 322 323 325 The Broker responds with the Topics it hosts: 327 331 332 335 338 339 341 In order to determine the exact nature of each Topic (i.e., in order 342 to find topics that publish incidents in the IODEF format), a 343 Platform would send an XMPP "disco#info" request to each Topic: 345 351 353 The Broker responds with the "disco#info" description, which MUST 354 include an XMPP Data Form [XEP-0004] including a 'pubsub#type' field 355 that specifies the supported namespace (in this example, the IODEF 356 namespace defined in [RFC7970]): 358 362 364 365 366 367 368 http://jabber.org/protocol/pubsub#meta-data 369 370 371 urn:ietf:params:xml:ns:iodef-2.0 372 373 374 375 377 The Platform discovers the topics by obtaining the Broker's response 378 and obtaining the namespaces returned in the "pubsub#type" field (in 379 the foregoing example, IODEF 2.0). 381 6. Publish-Subscribe 383 Using the XMPP publish-subscribe extension [XEP-0060], a Consumer 384 subscribes to a Topic and a Provider publishes information to that 385 Topic, which the Broker then distributes to all subscribed Consumers. 387 First, a Provider would create a Topic as follows: 389 393 394 395 396 398 Note: The foregoing example is the minimal protocol needed to create 399 a Topic with the default node configuration on the XMPP publish- 400 subscribe service specified in the 'to' address of the creation 401 request stanza. Depending on security requirements, the Provider 402 might need to request a non-default configuration for the node; see 403 [XEP-0060] for detailed examples. To also help with the Topic 404 configuration, the Provider may also optionally include 405 configurations parameters such as: 407 408 409 410 http://jabber.org/protocol/pubsub#node_config 411 412 authorize 413 1 414 never 415 416 418 The above configuration indicates the Topic is configured to enable 419 the XMPP-Controller to manage the subscriptions, be in persistent 420 mode and disables the Broker from cacheing the last item published. 421 Please refer to [XEP-0060] a more detailed description of these 422 configuration and other available configuration options. 424 Unless an error occurs (see [XEP-0060] for various error flows), the 425 Broker responds with success: 427 432 Second, a Consumer would subscribe as follows: 434 438 439 441 442 444 Unless an error occurs (see [XEP-0060] for various error flows), the 445 Broker responds with success: 447 451 452 456 457 459 Third, a Provider would publish an incident to the broker using the 460 MILEHost topic as follows: 462 466 467 468 469 475 476 492382 477 2015-07-18T09:00:00-05:00 478 479 480 contact@csirt.example.com 481 482 483 484 485 486 487 488 490 (The payload in the foregoing example is from [RFC7970]; payloads for 491 additional use cases can be found in [RFC8274].) 493 The Broker would then deliver that incident report to all Consumers 494 who are subscribed to the Topic: 496 500 501 502 503 509 510 492382 511 2015-07-18T09:00:00-05:00 512 513 514 contact@csirt.example.com 515 516 517 518 519 520 521 522 524 Note that [XEP-0060] uses the XMPP "" stanza for delivery 525 of content. To ensure that messages are delivered to the Consumer 526 even if the Consumer is not online at the same time that the 527 Publisher generates the message, an XMPP-Grid Controller MUST support 528 "offline messaging" delivery semantics as specified in [RFC6121], 529 best practices for which are further explained in [XEP-0160]. 531 7. IANA Considerations 533 This document has no actions for IANA. 535 8. Security Considerations 537 An XMPP-Grid Controller serves as an controlling broker for XMPP-Grid 538 Platforms such as Enforcement Points, Policy Servers, CMDBs, and 539 Sensors, using a publish-subscribe-search model of information 540 exchange and lookup. By increasing the ability of XMPP-Grid 541 Platforms to learn about and respond to security incident reports and 542 other security-relevant information, XMPP-Grid can improve the 543 timeliness and utility of the security system. However, this 544 integrated security system can also be exploited by attackers if they 545 can compromise it. Therefore, strong security protections for XMPP- 546 Grid are essential. 548 As XMPP is the core of this document, the security considerations of 549 [RFC6120] applies. In addition, as XMPP-Grid defines a specific 550 instance, this section provides a security analysis of the XMPP-Grid 551 data transfer protocol and the architectural elements that employ it, 552 specifically with respect to their use of this protocol. Three 553 subsections define the trust model (which elements are trusted to do 554 what), the threat model (attacks that can be mounted on the system), 555 and the countermeasures (ways to address or mitigate the threats 556 previously identified). 558 8.1. Trust Model 560 The first step in analyzing the security of the XMPP-Grid transport 561 protocol is to describe the trust model, listing what each 562 architectural element is trusted to do. The items listed here are 563 assumptions, but provisions are made in the Threat Model and 564 Countermeasures sections for elements that fail to perform as they 565 were trusted to do. 567 8.1.1. Network 569 The network used to carry XMPP-Grid messages (i.e., the underlying 570 network transport layer over which XMPP runs) is trusted to: 572 o Perform best effort delivery of network traffic 574 The network used to carry XMPP-Grid messages is not expected 575 (trusted) to: 577 o Provide confidentiality or integrity protection for messages sent 578 over it 580 o Provide timely or reliable service 582 8.1.2. XMPP-Grid Platforms 584 Authorized XMPP-Grid Platforms are trusted to: 586 o Preserve the confidentiality of sensitive data retrieved via the 587 XMPP-Grid Controller 589 8.1.3. XMPP-Grid Controller 591 The XMPP-Grid Controller (including its associated Broker) is trusted 592 to: 594 o Broker requests for data and enforce authorization of access to 595 this data throughout its lifecycle 597 o Perform service requests in a timely and accurate manner 599 o Create and maintain accurate operational attributes 601 o Only reveal data to and accept service requests from authorized 602 parties 604 o Preserve the integrity (and confidentiality against unauthorized 605 parties) of the data flowing through it. 607 The XMPP-Grid Controller is not expected (trusted) to: 609 o Verify the truth (correctness) of data 611 8.1.4. Certification Authority 613 To allow XMPP-Grid Platforms to mutually authenticate with XMPP-Grid 614 Controllers, it is expected that a Certification Authority (CA) is 615 employed to issue certificates. Such a CA (or each CA, if there are 616 several) is trusted to: 618 o Ensure that only proper certificates are issued and that all 619 certificates are issued in accordance with the CA's policies 621 o Revoke certificates previously issued when necessary 623 o Regularly and securely distribute certificate revocation 624 information 626 o Promptly detect and report any violations of this trust so that 627 they can be handled 629 The CA is not expected (trusted) to: 631 o Issue certificates that go beyond the XMPP-Grid needs or other 632 constraints imposed by a relying party. 634 8.2. Threat Model 636 To secure the XMPP-Grid data transfer protocol and the architectural 637 elements that implement it, this section identifies the attacks that 638 can be mounted against the protocol and elements. 640 8.2.1. Network Attacks 642 A variety of attacks can be mounted using the network. For the 643 purposes of this subsection the phrase "network traffic" can be taken 644 to mean messages and/or parts of messages. Any of these attacks can 645 be mounted by network elements, by parties who control network 646 elements, and (in many cases) by parties who control network-attached 647 devices. 649 o Network traffic can be passively monitored to glean information 650 from any unencrypted traffic 652 o Even if all traffic is encrypted, valuable information can be 653 gained by traffic analysis (volume, timing, source and destination 654 addresses, etc.) 656 o Network traffic can be modified in transit 658 o Previously transmitted network traffic can be replayed 660 o New network traffic can be added 662 o Network traffic can be blocked, perhaps selectively 664 o A "Man In The Middle" (MITM) attack can be mounted where an 665 attacker interposes itself between two communicating parties and 666 poses as the other end to either party or impersonates the other 667 end to either or both parties 669 o Undesired network traffic can be sent in an effort to overload an 670 architectural component, thus mounting a denial of service attack 672 8.2.2. XMPP-Grid Platforms 674 An unauthorized XMPP-Grid Platform (one which is not recognized by 675 the XMPP-Grid Controller or is recognized but not authorized to 676 perform any actions) cannot mount any attacks other than those listed 677 in the Network Attacks section above. 679 An authorized XMPP-Grid Platform, on the other hand, can mount many 680 attacks. These attacks might occur because the XMPP-Grid Platform is 681 controlled by a malicious, careless, or incompetent party (whether 682 because its owner is malicious, careless, or incompetent or because 683 the XMPP-Grid Platform has been compromised and is now controlled by 684 a party other than its owner). They might also occur because the 685 XMPP-Grid Platform is running malicious software; because the XMPP- 686 Grid Platform is running buggy software (which can fail in a state 687 that floods the network with traffic); or because the XMPP-Grid 688 Platform has been configured improperly. From a security standpoint, 689 it generally makes no difference why an attack is initiated. The 690 same countermeasures can be employed in any case. 692 Here is a list of attacks that can be mounted by an authorized XMPP- 693 Grid Platform: 695 o Cause many false alarms or otherwise overload the XMPP-Grid 696 Controller or other elements in the network security system 697 (including human administrators) leading to a denial of service or 698 disabling parts of the network security system 700 o Omit important actions (such as posting incriminating data), 701 resulting in incorrect access 703 o Use confidential information obtained from the XMPP-Grid 704 Controller to enable further attacks (such as using endpoint 705 health check results to exploit vulnerable endpoints) 707 o Advertise data crafted to exploit vulnerabilities in the XMPP-Grid 708 Controller or in other XMPP-Grid Platforms, with a goal of 709 compromising those systems 711 o Issue a search request or set up a subscription that matches an 712 enormous result, leading to resource exhaustion on the XMPP-Grid 713 Controller, the publishing XMPP-Grid Platform, and/or the network 715 o Establish a communication channel using another XMPP-Grid 716 Platform's session-id 718 o Advertise false data that leads to incorrect (e.g., potentially 719 attacker-controlled or -induced) behavior of XMPP-Grid Platforms, 720 by virtue of applying correct procdeures to the falsified input. 722 Dependencies of or vulnerabilities of authorized XMPP-Grid Platforms 723 can be exploited to effect these attacks. Another way to effect 724 these attacks is to gain the ability to impersonate an XMPP-Grid 725 Platform (through theft of the XMPP-Grid Platform's identity 726 credentials or through other means). Even a clock skew between the 727 XMPP-Grid Platform and XMPP-Grid Controller can cause problems if the 728 XMPP-Grid Platform assumes that old XMPP-Grid Platform data should be 729 ignored. 731 8.2.3. XMPP-Grid Controllers 733 An unauthorized XMPP-Grid Controller (one which is not trusted by 734 XMPP-Grid Platforms) cannot mount any attacks other than those listed 735 in the Network Attacks section above. 737 An authorized XMPP-Grid Controller can mount many attacks. Similar 738 to the XMPP-Grid Platform case described above, these attacks might 739 occur because the XMPP-Grid Controller is controlled by a malicious, 740 careless, or incompetent party (either an XMPP-Grid Controller 741 administrator or an attacker who has seized control of the XMPP-Grid 742 Controller). They might also occur because the XMPP-Grid Controller 743 is running malicious software, because the XMPP-Grid Controller is 744 running buggy software (which can fail in a state that corrupts data 745 or floods the network with traffic), or because the XMPP-Grid 746 Controller has been configured improperly. 748 All of the attacks listed for XMPP-Grid Platform above can be mounted 749 by the XMPP-Grid Controller. Detection of these attacks will be more 750 difficult since the XMPP-Grid Controller can create false operational 751 attributes and/or logs that imply some other party created any bad 752 data. 754 Additional XMPP-Grid Controller attacks can include: 756 o Expose different data to different XMPP-Grid Platforms to mislead 757 investigators or cause inconsistent behavior 759 o Mount an even more effective denial of service attack than a 760 single XMPP-Grid Platform could; some mechanisms include inducing 761 the many platforms to perform the same operation in an 762 amplification-style attack, completely refusing to pass any 763 traffic at all, or sending floods of traffic to (certain) 764 platforms or other targets. 766 o Obtain and cache XMPP-Grid Platform credentials so they can be 767 used to impersonate XMPP-Grid Platforms even after a breach of the 768 XMPP-Grid Controller is repaired. Some SASL mechanisms (including 769 the mandatory-to-implement SCRAM and EXTERNAL with TLS mutual 770 certificate-based authentication) do not admit this class of 771 attack, but others (such as PLAIN) are susceptible. 773 o Obtain and cache XMPP-Grid Controller administrator credentials so 774 they can be used to regain control of the XMPP-Grid Controller 775 after the breach of the XMPP-Grid Controller is repaired. 777 o Eavesdrop, inject or modify the data being transferred between 778 provider and consumer 780 Dependencies of or vulnerabilities of the XMPP-Grid Controller can be 781 exploited to obtain control of the XMPP-Grid Controller and effect 782 these attacks. 784 8.2.4. Certification Authority 786 A Certification Authority trusted to issue certificates for the XMPP- 787 Grid Controller and/or XMPP-Grid Platforms can mount several attacks: 789 o Issue certificates for unauthorized parties, enabling them to 790 impersonate authorized parties such as the XMPP-Grid Controller or 791 an XMPP-Grid Platform. This can lead to all the threats that can 792 be mounted by the certificate's subject. 794 o Issue certificates without following all of the CA's policies. 795 Because this can result in issuing certificates that can be used 796 to impersonate authorized parties, this can lead to all the 797 threats that can be mounted by the certificate's subject. 799 o Fail to revoke previously issued certificates that need to be 800 revoked. This can lead to undetected impersonation of the 801 certificate's subject or failure to revoke authorization of the 802 subject, and therefore can lead to all of the threats that can be 803 mounted by that subject. 805 o Fail to regularly and securely distribute certificate revocation 806 information. This can cause a relying party to accept a revoked 807 certificate, leading to undetected impersonation of the 808 certificate's subject or failure to revoke authorization of the 809 subject, and therefore can lead to all of the threats that can be 810 mounted by that subject. It can also cause a relying party to 811 refuse to proceed with a transaction because timely revocation 812 information is not available, even though the transaction should 813 be permitted to proceed. 815 o Allow the CA's private key to be revealed to an unauthorized 816 party. This can lead to all the threats above. Even worse, the 817 actions taken with the private key will not be known to the CA. 819 o Fail to promptly detect and report errors and violations of trust 820 so that relying parties can be promptly notified. This can cause 821 the threats listed earlier in this section to persist longer than 822 necessary, leading to many knock-on effects. 824 8.3. Countermeasures 826 Below are countermeasures for specific attack scenarios to the XMPP- 827 Grid infrastructure. 829 8.3.1. Securing the XMPP-Grid Data Transfer Protocol 831 To address network attacks, the XMPP-Grid data transfer protocol 832 described in this document requires that the XMPP-Grid messages MUST 833 be carried over TLS (minimally TLS 1.2 and preferrably TLS 1.3 834 [RFC8446]) as described in [RFC6120] and updated by [RFC7590]. The 835 XMPP-Grid Controller and XMPP-Grid Platforms SHOULD mutually 836 authenticate. The XMPP-Grid Platform MUST verify the XMPP-Grid 837 Controller's certificate and determine whether the XMPP-Grid 838 Controller is trusted by this XMPP-Grid Platform before completing 839 the TLS handshake. To ensure interoperability, implementations MUST 840 implement at least one of either the SASL EXTERNAL mechanism 841 [RFC4422] or the SASL SCRAM mechanism. When using the SASL SCRAM 842 mechanism, the SCRAM-SHA-256-PLUS variant SHOULD be preferred over 843 the SCRAM-SHA-256 variant; and SHA-256 variants [RFC7677] SHOULD be 844 preferred over SHA-1 variants [RFC5802]). XMPP-Grid Platforms and 845 XMPP-Grid Controllers using certificate-based authentication SHOULD 846 each verify the revocation status of the other party's certificate. 847 The selection of which XMPP-Grid Platform authentication technique to 848 use in any particular deployment is left to the administrator. 850 These protocol security measures provide protection against all the 851 network attacks listed in the above document section except denial of 852 service attacks. If protection against these denial of service 853 attacks is desired, ingress filtering, rate limiting per source IP 854 address, and other denial of service mitigation measures can be 855 employed. In addition, an XMPP-Grid Controller MAY automatically 856 disable a misbehaving XMPP-Grid Platform. 858 8.3.2. Securing XMPP-Grid Platforms 860 XMPP-Grid Platforms can be deployed in locations that are susceptible 861 to physical attacks. Physical security measures can be taken to 862 avoid compromise of XMPP-Grid Platforms, but these are not always 863 practical or completely effective. An alternative measure is to 864 configure the XMPP-Grid Controller to provide read-only access for 865 such systems. The XMPP-Grid Controller SHOULD also include a full 866 authorization model so that individual XMPP-Grid Platforms can be 867 configured to have only the privileges that they need. The XMPP-Grid 868 Controller MAY provide functional templates so that the administrator 869 can configure a specific XMPP-Grid Platform as a DHCP [RFC2131] 870 server and authorize only the operations and metadata types needed by 871 a DHCP server to be permitted for that XMPP-Grid Platform. These 872 techniques can reduce the negative impacts of a compromised XMPP-Grid 873 Platform without diminishing the utility of the overall system. 875 To handle attacks within the bounds of this authorization model, the 876 XMPP-Grid Controller MAY also include rate limits and alerts for 877 unusual XMPP-Grid Platform behavior. XMPP-Grid Controllers SHOULD 878 make it easy to revoke an XMPP-Grid Platform's authorization when 879 necessary. The XMPP-Grid Controller SHOULD include auditable logs of 880 XMPP-Grid Platform activities. 882 To avoid compromise of XMPP-Grid Platform, XMPP-Grid Platform SHOULD 883 be hardened against attack and minimized to reduce their attack 884 surface. They should be well managed to minimize vulnerabilities in 885 the underlying platform and in systems upon which the XMPP-Grid 886 Platform depends. Personnel with administrative access should be 887 carefully screened and monitored to detect problems as soon as 888 possible. 890 8.3.3. Securing XMPP-Grid Controllers 892 Because of the serious consequences of XMPP-Grid Controller 893 compromise, XMPP-Grid Controllers need to be especially well hardened 894 against attack and minimized to reduce their attack surface. They 895 need to be well managed to minimize vulnerabilities in the underlying 896 platform and in systems upon which the XMPP-Grid Controller depends. 897 Network security measures such as firewalls or intrusion detection 898 systems can be used to monitor and limit traffic to and from the 899 XMPP-Grid Controller. Personnel with administrative access ought to 900 be carefully screened and monitored to detect problems as soon as 901 possible. Administrators SHOULD NOT use password-based 902 authentication but SHOULD instead use non-reusable credentials and 903 multi-factor authentication (where available). Physical security 904 measures ought to be employed to prevent physical attacks on XMPP- 905 Grid Controllers. 907 To ease detection of XMPP-Grid Controller compromise should it occur, 908 XMPP-Grid Controller behavior should be monitored to detect unusual 909 behavior (such as a reboot, a large increase in traffic, or different 910 views of an information repository for similar XMPP-Grid Platforms). 911 It is a matter of local policy whether XMPP-Grid Platforms log and/or 912 notify administrators when peculiar XMPP-Grid Controller behavior is 913 detected, and whether read-only audit logs of security-relevant 914 information (especially administrative actions) are maintained; 915 however, such behavior is encouraged to aid in forensic analysis. 916 Furthermore, if compromise of an XMPP-Grid Controller is detected, a 917 careful analysis should be performed and any reusable credentials 918 that can have been compromised should be reissued. 920 To address the potential for the XMPP-Grid controller to eavesdrop, 921 modify or inject data, it would be desirable to deploy end-to-end 922 encryption between the provider and the consumer(s). Unfortunately, 923 because there is no standardized method for encryption of one-to-many 924 messages within XMPP, techniques for enforcing end-to-end encryption 925 are out of scope for this specification. 927 8.3.4. Broker Access Models for Topics 929 The XMPP publish-subscribe specification [XEP-0060] defines five 930 access models for subscribing to Topics at a Broker: open, presence, 931 roster, authorize, and whitelist. The first model allows 932 uncontrolled access and the next two models are appropriate only in 933 instant-messaging applications. Therefore, a Broker SHOULD support 934 only the authorize model (under which the Topic owner needs to 935 approve all subscription requests and only subscribers can retrieve 936 data items) and the whitelist model (under which only preconfigured 937 Platforms can subscribe or retrieve data items). In order to ease 938 the deployment burden, subscription approvals and whitelist 939 management can be automated (e.g, the Topic "owner" can be a policy 940 server). The choice between "authorize" and "whitelist" as the 941 default access model is a matter for local service policy. 943 8.3.5. Limit on Search Result Size 945 While XMPP-Grid is designed for high scalability to 100,000s of 946 Platforms, an XMPP-Grid Controller MAY establish a limit to the 947 amount of data it is willing to return in search or subscription 948 results. Platforms could use [XEP-0059] to restrict the size of the 949 result sets the Controller returns in search or subscription results 950 or topics' service discovery. This mitigates the threat of an XMPP- 951 Grid Platform causing resource exhaustion by issuing a search or 952 subscription that leads to an enormous result. 954 8.3.6. Securing the Certification Authority 956 As noted above, compromise of a Certification Authority (CA) trusted 957 to issue certificates for the XMPP-Grid Controller and/or XMPP-Grid 958 Platforms is a major security breach. Many guidelines for proper CA 959 security have been developed: the CA/Browser Forum's Baseline 960 Requirements, the AICPA/CICA Trust Service Principles, the IETF's 961 Certificate Transparency [RFC6962] etc. The CA operator and relying 962 parties should agree on an appropriately rigorous security practices 963 to be used. 965 Even with the most rigorous security practices, a CA can be 966 compromised. If this compromise is detected quickly, relying parties 967 can remove the CA from their list of trusted CAs, and other CAs can 968 revoke any certificates issued to the CA. However, CA compromise may 969 go undetected for some time, and there's always the possibility that 970 a CA is being operated improperly or in a manner that is not in the 971 interests of the relying parties. For this reason, relying parties 972 may wish to "pin" a small number of particularly critical 973 certificates (such as the certificate for the XMPP-Grid Controller). 974 Once a certificate has been pinned, the relying party will not accept 975 another certificate in its place unless the Administrator explicitly 976 commands it to do so. This does not mean that the relying party will 977 not check the revocation status of pinned certificates. However, the 978 Administrator can still be consulted if a pinned certificate is 979 revoked, since the CA and revocation process are not completely 980 trusted. By "pinning" one or a small set of certificates, the 981 relying party has the effective XMPP-Grid Controller(s) authorized to 982 connect to. 984 8.3.7. End-to-End Encryption of Messages 986 Because it is expected that there will be a relatively large number 987 of Consumers for every Topic, for purposes of content discovery and 988 scaling this document specifies a "one-to-many" communications 989 pattern using the XMPP Publish-Subscribe extension. Unfortunately, 990 there is no standardized technology for end-to-end encryption of one- 991 to-many messages in XMPP. This implies that messages can be subject 992 to eavesdropping, data injection, and data modification attacks 993 within a Broker or Controller. If it is necessary to mitigate 994 against such attacks, implementers would need to select a messaging 995 pattern other than [XEP-0060], most likely the basic "instant 996 messaging" pattern specified in [RFC6121] with a suitable XMPP 997 extension for end-to-end encryption (such as [RFC3923] or a more 998 modern method such as [XEP-0384]). The description of such an 999 approach is out of scope for this document. 1001 8.4. Summary 1003 XMPP-Grid's considerable value as a broker for security-sensitive 1004 data exchange distribution also makes the protocol and the network 1005 security elements that implement it a target for attack. Therefore, 1006 strong security has been included as a basic design principle within 1007 the XMPP-Grid design process. 1009 The XMPP-Grid data transfer protocol provides strong protection 1010 against a variety of different attacks. In the event that an XMPP- 1011 Grid Platform or XMPP-Grid Controller is compromised, the effects of 1012 this compromise have been reduced and limited with the recommended 1013 role-based authorization model and other provisions, and best 1014 practices for managing and protecting XMPP-Grid systems have been 1015 described. Taken together, these measures should provide protection 1016 commensurate with the threat to XMPP-Grid systems, thus ensuring that 1017 they fulfill their promise as a network security clearing-house. 1019 9. Privacy Considerations 1021 XMPP-Grid Platforms can publish information about endpoint health, 1022 network access, events (which can include information about what 1023 services an endpoint is accessing), roles and capabilities, and the 1024 identity of the end user operating the endpoint. Any of this 1025 published information can be queried by other XMPP-Grid Platforms and 1026 could potentially be used to correlate network activity to a 1027 particular end user. 1029 Dynamic and static information brokered by an XMPP-Grid Controller, 1030 ostensibly for purposes of correlation by XMPP-Grid Platforms for 1031 intrusion detection, could be misused by a broader set of XMPP-Grid 1032 Platforms which hitherto have been performing specific roles with 1033 strict well-defined separation of duties. 1035 Care needs to be taken by deployers of XMPP-Grid to ensure that the 1036 information published by XMPP-Grid Platforms does not violate 1037 agreements with end users or local and regional laws and regulations. 1038 This can be accomplished either by configuring XMPP-Grid Platforms to 1039 not publish certain information or by restricting access to sensitive 1040 data to trusted XMPP-Grid Platforms. That is, the easiest means to 1041 ensure privacy or protect sensitive data, is to omit or not share it 1042 at all. 1044 Similarly, care must be taken by deployers and XMPP-Grid Controller 1045 implementations as they implement the appropriate auditing tools. In 1046 particular, any information, such as logs must be sensitive to the 1047 type of information stored to ensure that the information does not 1048 violate privacy and agreements with end users or local and regional 1049 laws and regulations. 1051 Another consideration for deployers is to enable end-to-end 1052 encryption to ensure the data is protected from the data layer to 1053 data layer and thus protect it from the transport layer. The means 1054 to achieve end-to-end encrpytion is beyond the scope of this 1055 document. 1057 10. Operations and Management Considerations 1059 In order to facilitate the management of Providers and the onboarding 1060 of Consumers, it is helpful to generate the following ahead of time: 1062 o Agreement between the operators of Provider services and the 1063 implementers of Consumer software regarding identifiers for common 1064 Topics (e.g., these could be registered with the XMPP Software 1065 Foundation's registry of well-known nodes for service discovery 1066 and publish-subscribe located at ). 1069 o Security certificates (including appropriate certificate chains) 1070 for Controllers, including identification of any Providers 1071 associated with the Controllers (which might be located at 1072 subdomains). 1074 o Consistent and secure access control policies for publishing and 1075 subscribing to Topics. 1077 These matters are out of scope for this document but ought to be 1078 addressed by the XMPP-Grid community. 1080 11. Acknowledgements 1082 The authors would like to acknowledge the contributions, authoring 1083 and/or editing of the following people: Joseph Salowey, Lisa 1084 Lorenzin, Clifford Kahn, Henk Birkholz, Jessica Fitzgerald-McKay, 1085 Steve Hanna, and Steve Venema. In addition, we want to thank Takeshi 1086 Takahashi, Panos Kampanakis, Adam Montville, Chris Inacio, and Dave 1087 Cridland for reviewing and providing valuable comments. 1089 12. References 1091 12.1. Normative References 1093 [RFC2026] Bradner, S., "The Internet Standards Process -- Revision 1094 3", BCP 9, RFC 2026, DOI 10.17487/RFC2026, October 1996, 1095 . 1097 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1098 Requirement Levels", BCP 14, RFC 2119, 1099 DOI 10.17487/RFC2119, March 1997, 1100 . 1102 [RFC3923] Saint-Andre, P., "End-to-End Signing and Object Encryption 1103 for the Extensible Messaging and Presence Protocol 1104 (XMPP)", RFC 3923, DOI 10.17487/RFC3923, October 2004, 1105 . 1107 [RFC4422] Melnikov, A., Ed. and K. Zeilenga, Ed., "Simple 1108 Authentication and Security Layer (SASL)", RFC 4422, 1109 DOI 10.17487/RFC4422, June 2006, 1110 . 1112 [RFC5802] Newman, C., Menon-Sen, A., Melnikov, A., and N. Williams, 1113 "Salted Challenge Response Authentication Mechanism 1114 (SCRAM) SASL and GSS-API Mechanisms", RFC 5802, 1115 DOI 10.17487/RFC5802, July 2010, 1116 . 1118 [RFC6120] Saint-Andre, P., "Extensible Messaging and Presence 1119 Protocol (XMPP): Core", RFC 6120, DOI 10.17487/RFC6120, 1120 March 2011, . 1122 [RFC6121] Saint-Andre, P., "Extensible Messaging and Presence 1123 Protocol (XMPP): Instant Messaging and Presence", 1124 RFC 6121, DOI 10.17487/RFC6121, March 2011, 1125 . 1127 [RFC7590] Saint-Andre, P. and T. Alkemade, "Use of Transport Layer 1128 Security (TLS) in the Extensible Messaging and Presence 1129 Protocol (XMPP)", RFC 7590, DOI 10.17487/RFC7590, June 1130 2015, . 1132 [RFC7677] Hansen, T., "SCRAM-SHA-256 and SCRAM-SHA-256-PLUS Simple 1133 Authentication and Security Layer (SASL) Mechanisms", 1134 RFC 7677, DOI 10.17487/RFC7677, November 2015, 1135 . 1137 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1138 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1139 May 2017, . 1141 [XEP-0004] 1142 Eatmon, R., Hildebrand, J., Miller, J., Muldowney, T., and 1143 P. Saint-Andre, "Data Forms", XSF XEP 0004, August 2007. 1145 [XEP-0030] 1146 Hildebrand, J., Millard, P., Eatmon, R., and P. Saint- 1147 Andre, "Service Discovery", XSF XEP 0030, July 2010. 1149 [XEP-0059] 1150 Paterson, I., Saint-Andre, P., Mercier, V., and J. 1151 Seguineau, "Result Set Management", XSF XEP 0059, 1152 September 2006. 1154 [XEP-0060] 1155 Millard, P., Saint-Andre, P., and R. Meijer, "Publish- 1156 Subscribe", XSF XEP 0060, December 2017. 1158 [XEP-0203] 1159 Saint-Andre, P., "Delayed Delivery", XSF XEP 0203, 1160 December 2009. 1162 [XEP-0384] 1163 Straub, A., "Publish-Subscribe", XSF XEP 0384, July 2018. 1165 12.2. Informative References 1167 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", 1168 RFC 2131, DOI 10.17487/RFC2131, March 1997, 1169 . 1171 [RFC6962] Laurie, B., Langley, A., and E. Kasper, "Certificate 1172 Transparency", RFC 6962, DOI 10.17487/RFC6962, June 2013, 1173 . 1175 [RFC7970] Danyliw, R., "The Incident Object Description Exchange 1176 Format Version 2", RFC 7970, DOI 10.17487/RFC7970, 1177 November 2016, . 1179 [RFC8274] Kampanakis, P. and M. Suzuki, "Incident Object Description 1180 Exchange Format Usage Guidance", RFC 8274, 1181 DOI 10.17487/RFC8274, November 2017, 1182 . 1184 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 1185 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 1186 . 1188 [XEP-0160] 1189 Saint-Andre, P., "Publish-Subscribe", XSF XEP 0160, 1190 October 2016. 1192 Authors' Addresses 1194 Nancy Cam-Winget (editor) 1195 Cisco Systems 1196 3550 Cisco Way 1197 San Jose, CA 95134 1198 USA 1200 Email: ncamwing@cisco.com 1201 Syam Appala 1202 Cisco Systems 1203 3550 Cisco Way 1204 San Jose, CA 95134 1205 USA 1207 Email: syam1@cisco.com 1209 Scott Pope 1210 Cisco Systems 1211 5400 Meadows Road 1212 Suite 300 1213 Lake Oswego, OR 97035 1214 USA 1216 Email: scottp@cisco.com 1218 Peter Saint-Andre 1219 Mozilla 1221 Email: stpeter@mozilla.com