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2 MILE N. Cam-Winget, Ed.
3 Internet-Draft S. Appala
4 Intended status: Standards Track S. Pope
5 Expires: September 12, 2019 Cisco Systems
6 P. Saint-Andre
7 Mozilla
8 March 11, 2019
10 Using XMPP for Security Information Exchange
11 draft-ietf-mile-xmpp-grid-10
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 12, 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 . . . . . . . . . . . . . . . . . . . . . . 14
67 8.3. Countermeasures . . . . . . . . . . . . . . . . . . . . . 18
68 8.4. Summary . . . . . . . . . . . . . . . . . . . . . . . . . 21
69 9. Privacy Considerations . . . . . . . . . . . . . . . . . . . 22
70 10. Operations and Management Considerations . . . . . . . . . . 23
71 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 23
72 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 23
73 12.1. Normative References . . . . . . . . . . . . . . . . . . 23
74 12.2. Informative References . . . . . . . . . . . . . . . . . 25
75 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25
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 7. IANA Considerations
526 This document has no actions for IANA.
528 8. Security Considerations
530 An XMPP-Grid Controller serves as an controlling broker for XMPP-Grid
531 Platforms such as Enforcement Points, Policy Servers, CMDBs, and
532 Sensors, using a publish-subscribe-search model of information
533 exchange and lookup. By increasing the ability of XMPP-Grid
534 Platforms to learn about and respond to security incident reports and
535 other security-relevant information, XMPP-Grid can improve the
536 timeliness and utility of the security system. However, this
537 integrated security system can also be exploited by attackers if they
538 can compromise it. Therefore, strong security protections for XMPP-
539 Grid are essential.
541 As XMPP is the core of this document, the security considerations of
542 [RFC6120] applies. In addition, as XMPP-Grid defines a specific
543 instance, this section provides a security analysis of the XMPP-Grid
544 data transfer protocol and the architectural elements that employ it,
545 specifically with respect to their use of this protocol. Three
546 subsections define the trust model (which elements are trusted to do
547 what), the threat model (attacks that can be mounted on the system),
548 and the countermeasures (ways to address or mitigate the threats
549 previously identified).
551 8.1. Trust Model
553 The first step in analyzing the security of the XMPP-Grid transport
554 protocol is to describe the trust model, listing what each
555 architectural element is trusted to do. The items listed here are
556 assumptions, but provisions are made in the Threat Model and
557 Countermeasures sections for elements that fail to perform as they
558 were trusted to do.
560 8.1.1. Network
562 The network used to carry XMPP-Grid messages (i.e., the underlying
563 network transport layer over which XMPP runs) is trusted to:
565 o Perform best effort delivery of network traffic
567 The network used to carry XMPP-Grid messages is not expected
568 (trusted) to:
570 o Provide confidentiality or integrity protection for messages sent
571 over it
573 o Provide timely or reliable service
575 8.1.2. XMPP-Grid Platforms
577 Authorized XMPP-Grid Platforms are trusted to:
579 o Preserve the confidentiality of sensitive data retrieved via the
580 XMPP-Grid Controller
582 8.1.3. XMPP-Grid Controller
584 The XMPP-Grid Controller (including its associated Broker) is trusted
585 to:
587 o Broker requests for data and enforce authorization of access to
588 this data throughout its lifecycle
590 o Perform service requests in a timely and accurate manner
591 o Create and maintain accurate operational attributes
593 o Only reveal data to and accept service requests from authorized
594 parties
596 The XMPP-Grid Controller is not expected (trusted) to:
598 o Verify the truth (correctness) of data
600 8.1.4. Certification Authority
602 To allow XMPP-Grid Platforms to mutually authenticate with XMPP-Grid
603 Controllers, it is expected that a Certification Authority (CA) is
604 employed to issue certificates. Such a CA (or each CA, if there are
605 several) is trusted to:
607 o Ensure that only proper certificates are issued and that all
608 certificates are issued in accordance with the CA's policies
610 o Revoke certificates previously issued when necessary
612 o Regularly and securely distribute certificate revocation
613 information
615 o Promptly detect and report any violations of this trust so that
616 they can be handled
618 The CA is not expected (trusted) to:
620 o Issue certificates that go beyond the XMPP-Grid needs or other
621 constraints imposed by a relying party.
623 8.2. Threat Model
625 To secure the XMPP-Grid data transfer protocol and the architectural
626 elements that implement it, this section identifies the attacks that
627 can be mounted against the protocol and elements.
629 8.2.1. Network Attacks
631 A variety of attacks can be mounted using the network. For the
632 purposes of this subsection the phrase "network traffic" can be taken
633 to mean messages and/or parts of messages. Any of these attacks can
634 be mounted by network elements, by parties who control network
635 elements, and (in many cases) by parties who control network-attached
636 devices.
638 o Network traffic can be passively monitored to glean information
639 from any unencrypted traffic
641 o Even if all traffic is encrypted, valuable information can be
642 gained by traffic analysis (volume, timing, source and destination
643 addresses, etc.)
645 o Network traffic can be modified in transit
647 o Previously transmitted network traffic can be replayed
649 o New network traffic can be added
651 o Network traffic can be blocked, perhaps selectively
653 o A "Man In The Middle" (MITM) attack can be mounted where an
654 attacker interposes itself between two communicating parties and
655 poses as the other end to either party or impersonates the other
656 end to either or both parties
658 o Undesired network traffic can be sent in an effort to overload an
659 architectural component, thus mounting a denial of service attack
661 8.2.2. XMPP-Grid Platforms
663 An unauthorized XMPP-Grid Platform (one which is not recognized by
664 the XMPP-Grid Controller or is recognized but not authorized to
665 perform any actions) cannot mount any attacks other than those listed
666 in the Network Attacks section above.
668 An authorized XMPP-Grid Platform, on the other hand, can mount many
669 attacks. These attacks might occur because the XMPP-Grid Platform is
670 controlled by a malicious, careless, or incompetent party (whether
671 because its owner is malicious, careless, or incompetent or because
672 the XMPP-Grid Platform has been compromised and is now controlled by
673 a party other than its owner). They might also occur because the
674 XMPP-Grid Platform is running malicious software; because the XMPP-
675 Grid Platform is running buggy software (which can fail in a state
676 that floods the network with traffic); or because the XMPP-Grid
677 Platform has been configured improperly. From a security standpoint,
678 it generally makes no difference why an attack is initiated. The
679 same countermeasures can be employed in any case.
681 Here is a list of attacks that can be mounted by an authorized XMPP-
682 Grid Platform:
684 o Cause many false alarms or otherwise overload the XMPP-Grid
685 Controller or other elements in the network security system
686 (including human administrators) leading to a denial of service or
687 disabling parts of the network security system
689 o Omit important actions (such as posting incriminating data),
690 resulting in incorrect access
692 o Use confidential information obtained from the XMPP-Grid
693 Controller to enable further attacks (such as using endpoint
694 health check results to exploit vulnerable endpoints)
696 o Advertise data crafted to exploit vulnerabilities in the XMPP-Grid
697 Controller or in other XMPP-Grid Platforms, with a goal of
698 compromising those systems
700 o Issue a search request or set up a subscription that matches an
701 enormous result, leading to resource exhaustion on the XMPP-Grid
702 Controller, the publishing XMPP-Grid Platform, and/or the network
704 o Establish a communication channel using another XMPP-Grid
705 Platform's session-id
707 Dependencies of or vulnerabilities of authorized XMPP-Grid Platforms
708 can be exploited to effect these attacks. Another way to effect
709 these attacks is to gain the ability to impersonate an XMPP-Grid
710 Platform (through theft of the XMPP-Grid Platform's identity
711 credentials or through other means). Even a clock skew between the
712 XMPP-Grid Platform and XMPP-Grid Controller can cause problems if the
713 XMPP-Grid Platform assumes that old XMPP-Grid Platform data should be
714 ignored.
716 8.2.3. XMPP-Grid Controllers
718 An unauthorized XMPP-Grid Controller (one which is not trusted by
719 XMPP-Grid Platforms) cannot mount any attacks other than those listed
720 in the Network Attacks section above.
722 An authorized XMPP-Grid Controller can mount many attacks. Similar
723 to the XMPP-Grid Platform case described above, these attacks might
724 occur because the XMPP-Grid Controller is controlled by a malicious,
725 careless, or incompetent party (either an XMPP-Grid Controller
726 administrator or an attacker who has seized control of the XMPP-Grid
727 Controller). They might also occur because the XMPP-Grid Controller
728 is running malicious software, because the XMPP-Grid Controller is
729 running buggy software (which can fail in a state that corrupts data
730 or floods the network with traffic), or because the XMPP-Grid
731 Controller has been configured improperly.
733 All of the attacks listed for XMPP-Grid Platform above can be mounted
734 by the XMPP-Grid Controller. Detection of these attacks will be more
735 difficult since the XMPP-Grid Controller can create false operational
736 attributes and/or logs that imply some other party created any bad
737 data.
739 Additional XMPP-Grid Controller attacks can include:
741 o Expose different data to different XMPP-Grid Platforms to mislead
742 investigators or cause inconsistent behavior
744 o Mount an even more effective denial of service attack than a
745 single XMPP-Grid Platform could
747 o Obtain and cache XMPP-Grid Platform credentials so they can be
748 used to impersonate XMPP-Grid Platforms even after a breach of the
749 XMPP-Grid Controller is repaired
751 o Obtain and cache XMPP-Grid Controller administrator credentials so
752 they can be used to regain control of the XMPP-Grid Controller
753 after the breach of the XMPP-Grid Controller is repaired
755 o Eavesdrop, inject or modify the data being transferred between
756 provider and consumer
758 Dependencies of or vulnerabilities of the XMPP-Grid Controller can be
759 exploited to obtain control of the XMPP-Grid Controller and effect
760 these attacks.
762 8.2.4. Certification Authority
764 A Certification Authority trusted to issue certificates for the XMPP-
765 Grid Controller and/or XMPP-Grid Platforms can mount several attacks:
767 o Issue certificates for unauthorized parties, enabling them to
768 impersonate authorized parties such as the XMPP-Grid Controller or
769 an XMPP-Grid Platform. This can lead to all the threats that can
770 be mounted by the certificate's subject.
772 o Issue certificates without following all of the CA's policies.
773 Because this can result in issuing certificates that can be used
774 to impersonate authorized parties, this can lead to all the
775 threats that can be mounted by the certificate's subject.
777 o Fail to revoke previously issued certificates that need to be
778 revoked. This can lead to undetected impersonation of the
779 certificate's subject or failure to revoke authorization of the
780 subject, and therefore can lead to all of the threats that can be
781 mounted by that subject.
783 o Fail to regularly and securely distribute certificate revocation
784 information. This can cause a relying party to accept a revoked
785 certificate, leading to undetected impersonation of the
786 certificate's subject or failure to revoke authorization of the
787 subject, and therefore can lead to all of the threats that can be
788 mounted by that subject. It can also cause a relying party to
789 refuse to proceed with a transaction because timely revocation
790 information is not available, even though the transaction should
791 be permitted to proceed.
793 o Allow the CA's private key to be revealed to an unauthorized
794 party. This can lead to all the threats above. Even worse, the
795 actions taken with the private key will not be known to the CA.
797 o Fail to promptly detect and report errors and violations of trust
798 so that relying parties can be promptly notified. This can cause
799 the threats listed earlier in this section to persist longer than
800 necessary, leading to many knock-on effects.
802 8.3. Countermeasures
804 Below are countermeasures for specific attack scenarios to the XMPP-
805 Grid infrastructure.
807 8.3.1. Securing the XMPP-Grid Data Transfer Protocol
809 To address network attacks, the XMPP-Grid data transfer protocol
810 described in this document requires that the XMPP-Grid messages MUST
811 be carried over TLS (minimally TLS 1.2 [RFC8446]) as described in
812 [RFC6120] and updated by [RFC7590]. The XMPP-Grid Controller and
813 XMPP-Grid Platforms SHOULD mutually authenticate. The XMPP-Grid
814 Platform MUST verify the XMPP-Grid Controller's certificate and
815 determine whether the XMPP-Grid Controller is trusted by this XMPP-
816 Grid Platform before completing the TLS handshake. To ensure
817 interoperability, implementations MUST implement at least one of
818 either the SASL EXTERNAL mechanism [RFC4422] or the SASL SCRAM
819 mechanism. When using the SASL SCRAM mechanism, the SCRAM-SHA-
820 256-PLUS variant SHOULD be preferred over the SCRAM-SHA-256 variant;
821 and SHA-256 variants [RFC7677] SHOULD be preferred over SHA-1
822 variants [RFC5802]). XMPP-Grid Platforms and XMPP-Grid Controllers
823 using certificate-based authentication SHOULD each verify the
824 revocation status of the other party's certificate. The selection of
825 which XMPP-Grid Platform authentication technique to use in any
826 particular deployment is left to the administrator.
828 These protocol security measures provide protection against all the
829 network attacks listed in the above document section except denial of
830 service attacks. If protection against these denial of service
831 attacks is desired, ingress filtering, rate limiting per source IP
832 address, and other denial of service mitigation measures can be
833 employed. In addition, an XMPP-Grid Controller MAY automatically
834 disable a misbehaving XMPP-Grid Platform.
836 8.3.2. Securing XMPP-Grid Platforms
838 XMPP-Grid Platforms can be deployed in locations that are susceptible
839 to physical attacks. Physical security measures can be taken to
840 avoid compromise of XMPP-Grid Platforms, but these are not always
841 practical or completely effective. An alternative measure is to
842 configure the XMPP-Grid Controller to provide read-only access for
843 such systems. The XMPP-Grid Controller SHOULD also include a full
844 authorization model so that individual XMPP-Grid Platforms can be
845 configured to have only the privileges that they need. The XMPP-Grid
846 Controller MAY provide functional templates so that the administrator
847 can configure a specific XMPP-Grid Platform as a DHCP [RFC2131]
848 server and authorize only the operations and metadata types needed by
849 a DHCP server to be permitted for that XMPP-Grid Platform. These
850 techniques can reduce the negative impacts of a compromised XMPP-Grid
851 Platform without diminishing the utility of the overall system.
853 To handle attacks within the bounds of this authorization model, the
854 XMPP-Grid Controller MAY also include rate limits and alerts for
855 unusual XMPP-Grid Platform behavior. XMPP-Grid Controllers SHOULD
856 make it easy to revoke an XMPP-Grid Platform's authorization when
857 necessary. The XMPP-Grid Controller SHOULD include auditable logs of
858 XMPP-Grid Platform activities.
860 To avoid compromise of XMPP-Grid Platform, XMPP-Grid Platform SHOULD
861 be hardened against attack and minimized to reduce their attack
862 surface. They should be well managed to minimize vulnerabilities in
863 the underlying platform and in systems upon which the XMPP-Grid
864 Platform depends. Personnel with administrative access should be
865 carefully screened and monitored to detect problems as soon as
866 possible.
868 8.3.3. Securing XMPP-Grid Controllers
870 Because of the serious consequences of XMPP-Grid Controller
871 compromise, XMPP-Grid Controllers need to be especially well hardened
872 against attack and minimized to reduce their attack surface. They
873 need to be well managed to minimize vulnerabilities in the underlying
874 platform and in systems upon which the XMPP-Grid Controller depends.
875 Network security measures such as firewalls or intrusion detection
876 systems can be used to monitor and limit traffic to and from the
877 XMPP-Grid Controller. Personnel with administrative access ought to
878 be carefully screened and monitored to detect problems as soon as
879 possible. Administrators SHOULD NOT use password-based
880 authentication but SHOULD instead use non-reusable credentials and
881 multi-factor authentication (where available). Physical security
882 measures ought to be employed to prevent physical attacks on XMPP-
883 Grid Controllers.
885 To ease detection of XMPP-Grid Controller compromise should it occur,
886 XMPP-Grid Controller behavior should be monitored to detect unusual
887 behavior (such as a reboot, a large increase in traffic, or different
888 views of an information repository for similar XMPP-Grid Platforms).
889 It is a matter of local policy whether XMPP-Grid Platforms log and/or
890 notify administrators when peculiar XMPP-Grid Controller behavior is
891 detected, and whether read-only audit logs of security-relevant
892 information (especially administrative actions) are maintained;
893 however, such behavior is encouraged to aid in forensic analysis.
894 Furthermore, if compromise of an XMPP-Grid Controller is detected, a
895 careful analysis should be performed and any reusable credentials
896 that can have been compromised should be reissued.
898 To address the potential for the XMPP-Grid controller to eavesdrop,
899 modify or inject data, it would be desirable to deploy end-to-end
900 encryption between the provider and the consumer(s). Unfortunately,
901 because there is no standardized method for encryption of one-to-many
902 messages within XMPP, techniques for enforcing end-to-end encryption
903 are out of scope for this specification.
905 8.3.4. Broker Access Models for Topics
907 The XMPP publish-subscribe specification [XEP-0060] defines five
908 access models for subscribing to Topics at a Broker: open, presence,
909 roster, authorize, and whitelist. The first model allows
910 uncontrolled access and the next two models are appropriate only in
911 instant-messaging applications. Therefore, a Broker SHOULD support
912 only the authorize model (under which the Topic owner needs to
913 approve all subscription requests and only subscribers can retrieve
914 data items) and the whitelist model (under which only preconfigured
915 Platforms can subscribe or retrieve data items). In order to ease
916 the deployment burden, subscription approvals and whitelist
917 management can be automated (e.g, the Topic "owner" can be a policy
918 server). The choice between "authorize" and "whitelist" as the
919 default access model is a matter for local service policy.
921 8.3.5. Limit on Search Result Size
923 While XMPP-Grid is designed for high scalability to 100,000s of
924 Platforms, an XMPP-Grid Controller MAY establish a limit to the
925 amount of data it is willing to return in search or subscription
926 results. Platforms could use [XEP-0059] to restrict the size of the
927 result sets the Controller returns in search or subscription results
928 or topics' service discovery. This mitigates the threat of an XMPP-
929 Grid Platform causing resource exhaustion by issuing a search or
930 subscription that leads to an enormous result.
932 8.3.6. Securing the Certification Authority
934 As noted above, compromise of a Certification Authority (CA) trusted
935 to issue certificates for the XMPP-Grid Controller and/or XMPP-Grid
936 Platforms is a major security breach. Many guidelines for proper CA
937 security have been developed: the CA/Browser Forum's Baseline
938 Requirements, the AICPA/CICA Trust Service Principles, the IETF's
939 Certificate Transparency [RFC6962] etc. The CA operator and relying
940 parties should agree on an appropriately rigorous security practices
941 to be used.
943 Even with the most rigorous security practices, a CA can be
944 compromised. If this compromise is detected quickly, relying parties
945 can remove the CA from their list of trusted CAs, and other CAs can
946 revoke any certificates issued to the CA. However, CA compromise may
947 go undetected for some time, and there's always the possibility that
948 a CA is being operated improperly or in a manner that is not in the
949 interests of the relying parties. For this reason, relying parties
950 may wish to "pin" a small number of particularly critical
951 certificates (such as the certificate for the XMPP-Grid Controller).
952 Once a certificate has been pinned, the relying party will not accept
953 another certificate in its place unless the Administrator explicitly
954 commands it to do so. This does not mean that the relying party will
955 not check the revocation status of pinned certificates. However, the
956 Administrator can still be consulted if a pinned certificate is
957 revoked, since the CA and revocation process are not completely
958 trusted. By "pinning" one or a small set of certificates, the
959 relying party has the effective XMPP-Grid Controller(s) authorized to
960 connect to.
962 8.4. Summary
964 XMPP-Grid's considerable value as a broker for security-sensitive
965 data exchange distribution also makes the protocol and the network
966 security elements that implement it a target for attack. Therefore,
967 strong security has been included as a basic design principle within
968 the XMPP-Grid design process.
970 The XMPP-Grid data transfer protocol provides strong protection
971 against a variety of different attacks. In the event that an XMPP-
972 Grid Platform or XMPP-Grid Controller is compromised, the effects of
973 this compromise have been reduced and limited with the recommended
974 role-based authorization model and other provisions, and best
975 practices for managing and protecting XMPP-Grid systems have been
976 described. Taken together, these measures should provide protection
977 commensurate with the threat to XMPP-Grid systems, thus ensuring that
978 they fulfill their promise as a network security clearing-house.
980 9. Privacy Considerations
982 XMPP-Grid Platforms can publish information about endpoint health,
983 network access, events (which can include information about what
984 services an endpoint is accessing), roles and capabilities, and the
985 identity of the end user operating the endpoint. Any of this
986 published information can be queried by other XMPP-Grid Platforms and
987 could potentially be used to correlate network activity to a
988 particular end user.
990 Dynamic and static information brokered by an XMPP-Grid Controller,
991 ostensibly for purposes of correlation by XMPP-Grid Platforms for
992 intrusion detection, could be misused by a broader set of XMPP-Grid
993 Platforms which hitherto have been performing specific roles with
994 strict well-defined separation of duties.
996 Care needs to be taken by deployers of XMPP-Grid to ensure that the
997 information published by XMPP-Grid Platforms does not violate
998 agreements with end users or local and regional laws and regulations.
999 This can be accomplished either by configuring XMPP-Grid Platforms to
1000 not publish certain information or by restricting access to sensitive
1001 data to trusted XMPP-Grid Platforms. That is, the easiest means to
1002 ensure privacy or protect sensitive data, is to omit or not share it
1003 at all.
1005 Similarly, care must be taken by deployers and XMPP-Grid Controller
1006 implementations as they implement the appropriate auditing tools. In
1007 particular, any information, such as logs must be sensitive to the
1008 type of information stored to ensure that the information does not
1009 violate privacy and agreements with end users or local and regional
1010 laws and regulations.
1012 Another consideration for deployers is to enable end-to-end
1013 encryption to ensure the data is protected from the data layer to
1014 data layer and thus protect it from the transport layer. The means
1015 to achieve end-to-end encrpytion is beyond the scope of this
1016 document.
1018 10. Operations and Management Considerations
1020 In order to facilitate the management of Providers and the onboarding
1021 of Consumers, it is helpful to generate the following ahead of time:
1023 o Agreement between the operators of Provider services and the
1024 implementers of Consumer software regarding identifiers for common
1025 Topics (e.g., these could be registered with the XMPP Software
1026 Foundation's registry of well-known nodes for service discovery
1027 and publish-subscribe located at ).
1030 o Security certificates (including appropriate certificate chains)
1031 for Controllers, including identification of any Providers
1032 associated with the Controllers (which might be located at
1033 subdomains).
1035 o Consistent and secure access control policies for publishing and
1036 subscribing to Topics.
1038 These matters are out of scope for this document but ought to be
1039 addressed by the XMPP-Grid community.
1041 11. Acknowledgements
1043 The authors would like to acknowledge the contributions, authoring
1044 and/or editing of the following people: Joseph Salowey, Lisa
1045 Lorenzin, Clifford Kahn, Henk Birkholz, Jessica Fitzgerald-McKay,
1046 Steve Hanna, and Steve Venema. In addition, we want to thank Takeshi
1047 Takahashi, Panos Kampanakis, Adam Montville, Chris Inacio, and Dave
1048 Cridland for reviewing and providing valuable comments.
1050 12. References
1052 12.1. Normative References
1054 [RFC2026] Bradner, S., "The Internet Standards Process -- Revision
1055 3", BCP 9, RFC 2026, DOI 10.17487/RFC2026, October 1996,
1056 .
1058 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
1059 Requirement Levels", BCP 14, RFC 2119,
1060 DOI 10.17487/RFC2119, March 1997,
1061 .
1063 [RFC4422] Melnikov, A., Ed. and K. Zeilenga, Ed., "Simple
1064 Authentication and Security Layer (SASL)", RFC 4422,
1065 DOI 10.17487/RFC4422, June 2006,
1066 .
1068 [RFC5802] Newman, C., Menon-Sen, A., Melnikov, A., and N. Williams,
1069 "Salted Challenge Response Authentication Mechanism
1070 (SCRAM) SASL and GSS-API Mechanisms", RFC 5802,
1071 DOI 10.17487/RFC5802, July 2010,
1072 .
1074 [RFC6120] Saint-Andre, P., "Extensible Messaging and Presence
1075 Protocol (XMPP): Core", RFC 6120, DOI 10.17487/RFC6120,
1076 March 2011, .
1078 [RFC7590] Saint-Andre, P. and T. Alkemade, "Use of Transport Layer
1079 Security (TLS) in the Extensible Messaging and Presence
1080 Protocol (XMPP)", RFC 7590, DOI 10.17487/RFC7590, June
1081 2015, .
1083 [RFC7677] Hansen, T., "SCRAM-SHA-256 and SCRAM-SHA-256-PLUS Simple
1084 Authentication and Security Layer (SASL) Mechanisms",
1085 RFC 7677, DOI 10.17487/RFC7677, November 2015,
1086 .
1088 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
1089 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
1090 May 2017, .
1092 [XEP-0004]
1093 Eatmon, R., Hildebrand, J., Miller, J., Muldowney, T., and
1094 P. Saint-Andre, "Data Forms", XSF XEP 0004, August 2007.
1096 [XEP-0030]
1097 Hildebrand, J., Millard, P., Eatmon, R., and P. Saint-
1098 Andre, "Service Discovery", XSF XEP 0030, July 2010.
1100 [XEP-0059]
1101 Paterson, I., Saint-Andre, P., Mercier, V., and J.
1102 Seguineau, "Result Set Management", XSF XEP 0059,
1103 September 2006.
1105 [XEP-0060]
1106 Millard, P., Saint-Andre, P., and R. Meijer, "Publish-
1107 Subscribe", XSF XEP 0060, December 2017.
1109 [XEP-0203]
1110 Saint-Andre, P., "Delayed Delivery", XSF XEP 0203,
1111 December 2009.
1113 12.2. Informative References
1115 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
1116 RFC 2131, DOI 10.17487/RFC2131, March 1997,
1117 .
1119 [RFC6962] Laurie, B., Langley, A., and E. Kasper, "Certificate
1120 Transparency", RFC 6962, DOI 10.17487/RFC6962, June 2013,
1121 .
1123 [RFC7970] Danyliw, R., "The Incident Object Description Exchange
1124 Format Version 2", RFC 7970, DOI 10.17487/RFC7970,
1125 November 2016, .
1127 [RFC8274] Kampanakis, P. and M. Suzuki, "Incident Object Description
1128 Exchange Format Usage Guidance", RFC 8274,
1129 DOI 10.17487/RFC8274, November 2017,
1130 .
1132 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
1133 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
1134 .
1136 Authors' Addresses
1138 Nancy Cam-Winget (editor)
1139 Cisco Systems
1140 3550 Cisco Way
1141 San Jose, CA 95134
1142 USA
1144 Email: ncamwing@cisco.com
1146 Syam Appala
1147 Cisco Systems
1148 3550 Cisco Way
1149 San Jose, CA 95134
1150 USA
1152 Email: syam1@cisco.com
1153 Scott Pope
1154 Cisco Systems
1155 5400 Meadows Road
1156 Suite 300
1157 Lake Oswego, OR 97035
1158 USA
1160 Email: scottp@cisco.com
1162 Peter Saint-Andre
1163 Mozilla
1165 Email: stpeter@mozilla.com