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Versions: (draft-appala-mile-xmpp-grid) 00 01 02 03 04 05 06 07

MILE                                                  N. Cam-Winget, Ed.
Internet-Draft                                                 S. Appala
Intended status: Standards Track                                 S. Pope
Expires: April 21, 2019                                    Cisco Systems
                                                          P. Saint-Andre
                                                                 Mozilla
                                                        October 18, 2018


              Using XMPP for Security Information Exchange
                      draft-ietf-mile-xmpp-grid-07

Abstract

   This document describes how to use the Extensible Messaging and
   Presence Protocol (XMPP) to collect and distribute security-relevant
   information between network-connected devices.  To illustrate the
   principles involved, this document describes such a usage for the
   Incident Object Description Exchange Format (IODEF).

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 21, 2019.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must



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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Architecture  . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Workflow  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Service Discovery . . . . . . . . . . . . . . . . . . . . . .   7
   6.  Publish-Subscribe . . . . . . . . . . . . . . . . . . . . . .   8
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
     8.1.  Trust Model . . . . . . . . . . . . . . . . . . . . . . .  12
     8.2.  Threat Model  . . . . . . . . . . . . . . . . . . . . . .  13
     8.3.  Countermeasures . . . . . . . . . . . . . . . . . . . . .  17
     8.4.  Summary . . . . . . . . . . . . . . . . . . . . . . . . .  20
   9.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  21
   10. Operations and Management Considerations  . . . . . . . . . .  21
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  22
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  22
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  22
     12.2.  Informative References . . . . . . . . . . . . . . . . .  23
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  23

1.  Introduction

   This document describes "XMPP-Grid": a method for using the
   Extensible Messaging and Presence Protocol (XMPP) [RFC6120] to
   collect and distribute security-relevant information among network
   platforms, endpoints, and any other network-connected device.  Among
   other things, XMPP provides a publish-subscribe service [XEP-0060]
   that acts as a broker, enabling control-plane functions by which
   entities can discover available information to be published or
   consumed.  Although such information can take the form of any
   structured data (XML, JSON, etc.), this document illustrates the
   principles of XMPP-Grid with examples that use the Incident Object
   Description Exchange Format (IODEF) [RFC7970].  That is, while other
   security information formats can be shared using XMPP, this document
   uses IODEF as one such example format that can be published and
   consumed using XMPP.

2.  Terminology

   This document uses XMPP terminology defined in [RFC6120] and
   [XEP-0060].  Because the intended audience for this document is those




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   who implement and deploy security reporting systems, mappings are
   provided for the benefit of XMPP developers and operators.

   Broker:  A specific type of controller containing control plane
      functions; as used here, the term refers to an XMPP publish-
      subscribe service.

   Broker Flow:  A method by which security-related information is
      published and consumed in a mediated fashion through a Broker.  In
      this flow, the Broker handles authorization of Consumers and
      Providers to Topics, receives messages from Providers, and
      delivers published messages to Consumers.

   Consumer:  An entity that contains functions to receive information
      from other components; as used here, the term refers to an XMPP
      publish-subscribe Subscriber.

   Controller:  A "component containing control plane functions that
      manage and facilitate information sharing or execute on security
      functions"; as used here, the term refers to an XMPP server, which
      provides core message delivery [RFC6120] used by publish-subscribe
      entities.

   Node:  The XMPP term for a Topic.

   Platform:  Any entity that connects to the XMPP-Grid in order to
      publish or consume security-related data.

   Provider:  An entity that contains functions to provide information
      to other components; as used here, the term refers to an XMPP
      publish-subscribe Publisher.

   Topic:  A contextual information channel created on a Broker at which
      messages generated by a Provider are propagated in real time to
      one or more Consumers.  Each Topic is limited to a specific type
      and format of security data (e.g.  IODEF namespace) and provides
      an XMPP interface by which the data can be obtained.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

3.  Architecture

   The following figure illustrates the architecture of XMPP-Grid.






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             +--------------------------------------+
             | +--------------------------------------+
             | | +--------------------------------------+
             | | |                                      |
             +-| |             Platforms                |
               +-|                                      |
                 +--------------------------------------+
                   /   \         /   \            /   \
                  /  C  \       /     \          /     \
                  -  o  -       -  d  -          -     -
                   ||n||A        | a  |B          |   |C
                   ||t||         | t  |           |   |
                  -  r  -       -  a  -           |   |
                  \  o  /       \     /           |   |
                   \ l /         \   /            |   |
                /|---------------------|\         |   |
         /|----/                         \--------| d |--|\
        /     /        Controller         \ ctrl  | a |    \
        \     \        & Broker           / plane | t |    /
         \|----\                         /--------| a |--|/
                \|---------------------|/         |   |
                   /   \         /   \            |   |
                  /  C  \       /     \           |   |
                  -  o  -       -  d  -           |   |
                   ||n||A        | a |B           |   |C
                   ||t||         | t |            |   |
                  -  r  -       -  a  -          -     -
                  \  o  /       \     /          \     /
                   \ l /         \   /            \   /
                 +------------------------------------+
                 |                                    |-+
                 |            Platforms               | |
                 |                                    | |-+
                 +------------------------------------+ | |
                   +------------------------------------+ |
                     +------------------------------------+

                     Figure 1: XMPP-Grid Architecture

   Platforms connect to the Controller (XMPP server) to authenticate and
   then establish appropriate authorizations to be a Provider or
   Consumer of interested Topics at the Broker.  The control plane
   messaging is established through XMPP and shown as "A" (control plane
   interface) in Figure 1.  Authorized nodes can then share data either
   through the Broker (shown as "B" in Figure 1) or in some cases
   directly (shown as "C" in Figure 1).  This document focuses primarily
   on the Broker Flow for information sharing ("direct flow"
   interactions can be used for specialized purposes such as bulk data



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   transfer, but methods for doing so are outside the scope of this
   document).

4.  Workflow

   A typical XMPP-Grid workflow is as follows:

   a.  A Platform with a source of security data requests connection to
       the XMPP-Grid via a Controller.

   b.  The Controller authenticates the Platform.

   c.  The Platform establishes authorized privileges (e.g. privilege to
       publish and/or subscribe to one or more Topics) with a Broker.

   d.  The Platform can publish security-related data to a Topic,
       subscribe to a Topic, query a Topic, or any combination of these
       operations.

   e.  A Provider unicasts its Topic updates to the Grid in real time
       through a Broker.  The Broker handles replication and
       distribution of the Topic to Consumers.  A Provider can publish
       the same or different data to multiple Topics.

   f.  Any Platform on the Grid can subscribe to any Topics published to
       the Grid (as permitted by authorization policy), and (as
       Consumers) will then receive a continual, real-time stream of
       updates from the Topics to which it is subscribed.

   The general workflow is summarized in the figure below:





















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   +--------------+         +------------+           +---------------+
   | IODEF Client |         | Controller |           | IODEF Service |
   |  (Consumer)  |         |  & Broker  |           |  (Provider)   |
   +--------------+         +------------+           +---------------+
           |                      |                         |
           |  Establish XMPP      |                         |
           |  Client Session      |                         |
           |  (RFC 6120)          |                         |
           |--------------------->|                         |
           |                      | Establish XMPP          |
           |                      | Client Session          |
           |                      | (RFC 6120)              |
           |                      |<------------------------|
           |                      | Request Topic Creation  |
           |                      | (XEP-0060)              |
           |                      |<------------------------|
           |                      | Topic Creation Success  |
           |                      | (XEP-0060)              |
           |                      |------------------------>|
           | Request Topic List   |                         |
           | (XEP-0030)           |                         |
           |--------------------->|                         |
           | Return Topic List    |                         |
           | (XEP-0030)           |                         |
           |<---------------------|                         |
           |                      |                         |
           | Query Each Topic     |                         |
           | (XEP-0030)           |                         |
           |--------------------->|                         |
           | Return Topic Data    |                         |
           | Including Topic Type |                         |
           | (XEP-0030)           |                         |
           |<---------------------|                         |
           |                      |                         |
           | Subscribe to IODEF   |                         |
           | Topic (XEP-0060)     |                         |
           |--------------------->|                         |
           | Subscription Success |                         |
           | (XEP-0060)           |                         |
           |<---------------------|                         |
           |                      | Publish IODEF Incident  |
           |                      | (XEP-0060)              |
           | Receive IODEF        |<------------------------|
           | Incident (XEP-0060)  |                         |
           |<---------------------|                         |
           |                      |                         |

                     Figure 2: IODEF Example Workflow



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   XMPP-Grid implementations MUST adhere to the mandatory-to-implement
   and mandatory-to-negotiate features as defined in [RFC6120].
   Similarly, implementations MUST implement [XEP-0060] to facilitate
   the asynchronous sharing for information.  The Service Discovery per
   [XEP-0030] SHOULD be implemented to facilitate the means to
   dynamically discover the available information and namespaces
   (Topics) to be published or consumed.

   The following sections provide protocol examples for the service
   discovery and publish-subscribe parts of the workflow.

5.  Service Discovery

   Using the XMPP service discovery extension [XEP-0030], a Controller
   enables Platforms to discover what information can be consumed
   through the Broker, and at which Topics.  As an example, the
   Controller at 'security-grid.example' might provide a Broker at
   'broker.security-grid.example' hosting a number of Topics.  A
   Platform at 'xmpp-grid-client@mile-host.example' would query the
   Broker about its available Topics by sending an XMPP "disco#items"
   request to the Broker:

   <iq type='get'
       from='xmpp-grid-client@mile-host.example/2EBE702A97D6'
       to='broker.security-grid.example'
       id='B3C17F7B-B9EF-4ABA-B08D-805DA9F34626'>
     <query xmlns='http://jabber.org/protocol/disco#items'/>
   </iq>

   The Broker responds with the Topics it hosts:

   <iq type='result'
       from='broker.security-grid.example'
       to='xmpp-grid-client@mile-host.example/2EBE702A97D6'
       id='B3C17F7B-B9EF-4ABA-B08D-805DA9F34626'>
     <query xmlns='http://jabber.org/protocol/disco#items'>
       <item node='NEA1'
             name='Endpoint Posture Information'
             jid='broker.security-grid.example'/>
       <item node='MILEHost'
             name='MILE Host Data'
             jid='broker.security-grid.example'/>
     </query>
   </iq>

   In order to determine the exact nature of each Topic (i.e., in order
   to find topics that publish incidents in the IODEF format), a
   Platform would send an XMPP "disco#info" request to each Topic:



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   <iq type='get'
       from='xmpp-grid-client@mile-host.example/2EBE702A97D6'
       to='broker.security-grid.example'
       id='D367D4ED-2795-489C-A83E-EAAFA07A0356'
     <query xmlns='http://jabber.org/protocol/disco#info'
            node='MILEHost'/>
   </iq>

   The Broker responds with the "disco#info" description, which SHOULD
   include an XMPP Data Form [XEP-0004] including a 'pubsub#type' field
   that specifies the supported namespace (in this example, the IODEF
   namespace defined in [RFC7970]):

 <iq type='result'
     from='broker.security-grid.example'
     to='xmpp-grid-client@mile-host.example/2EBE702A97D6'
     id='D367D4ED-2795-489C-A83E-EAAFA07A0356'/>
   <query xmlns='http://jabber.org/protocol/disco#info'
          node='MILEHost'>
     <identity category='pubsub' type='leaf'/>
     <feature var='http://jabber.org/protocol/pubsub'/>
     <x xmlns='jabber:x:data' type='result'>
       <field var='FORM_TYPE' type='hidden'>
         <value>http://jabber.org/protocol/pubsub#meta-data</value>
       </field>
       <field var='pubsub#type' label='Payload type' type='text-single'>
         <value>urn:ietf:params:xml:ns:iodef-2.0</value>
       </field>
     </x>
   </query>
 </iq>

6.  Publish-Subscribe

   Using the XMPP publish-subscribe extension [XEP-0030], a Consumer
   subscribes to a Topic and a Provider publishes information to that
   Topic, which the Broker then distributes to all subscribed Consumers.

   First, a Provider would create a Topic as follows:

   <iq type='set'
       from='datasource@provider.example/F12C2EFC9BB0'
       to='broker.security-grid.example'
       id='A67507DF-2F22-4937-8D30-88D2F7DBA279'>
     <pubsub xmlns='http://jabber.org/protocol/pubsub'>
       <create node='MILEHost'/>
     </pubsub>
   </iq>



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   Note: The foregoing example is the minimal protocol needed to create
   a Topic with the default node configuration on the XMPP publish-
   subscribe service specified in the 'to' address of the creation
   request stanza.  Depending on security requirements, the Provider
   might need to request a non-default configuration for the node; see
   [XEP-0060] for detailed examples.

   Unless an error occurs (see [XEP-0060] for various error flows), the
   Broker responds with success:

   <iq type='result'
       from='broker.security-grid.example'
       to='datasource@provider.example/F12C2EFC9BB0'
       id='A67507DF-2F22-4937-8D30-88D2F7DBA279'/>

   Second, a Consumer would subscribe as follows:

   <iq type='set'
       from='xmpp-grid-client@mile-host.example/2EBE702A97D6'
       to='broker.security-grid.example'
       id='9C6EEE9E-F09A-4418-8D68-3BA6AF852522'>
     <pubsub xmlns='http://jabber.org/protocol/pubsub'>
       <subscribe node='MILEHost'
                  jid='xmpp-grid-client@mile-host.example'/>
     </pubsub>
   </iq>

   Unless an error occurs (see [XEP-0060] for various error flows), the
   Broker responds with success:

   <iq type='result'
       from='broker.security-grid.example'
       to='xmpp-grid-client@mile-host.example/2EBE702A97D6'
       id='9C6EEE9E-F09A-4418-8D68-3BA6AF852522'>
     <pubsub xmlns='http://jabber.org/protocol/pubsub'>
       <subscription
           node='MILEHost'
           jid='xmpp-grid-client@mile-host.example'
           subscription='subscribed'/>
     </pubsub>
   </iq>

   Third, a Provider would publish an incident as follows:








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  <iq type='set'
      from='datasource@provider.example/F12C2EFC9BB0'
      to='broker.security-grid.example'
      id='2A17D283-0DAE-4A6C-85A9-C10B1B40928C'>
    <pubsub xmlns='http://jabber.org/protocol/pubsub'>
      <publish node='MILEHost'>
        <item id='8bh1g27skbga47fh9wk7'>
          <IODEF-Document version="2.00" xml:lang="en"
            xmlns="urn:ietf:params:xml:ns:iodef-2.0"
            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation=
              "http://www.iana.org/assignments/xml-registry/
               schema/iodef-2.0.xsd">
            <Incident purpose="reporting" restriction="private">
              <IncidentID name="csirt.example.com">492382</IncidentID>
              <GenerationTime>2015-07-18T09:00:00-05:00</GenerationTime>
              <Contact type="organization" role="creator">
                <Email>
                  <EmailTo>contact@csirt.example.com</EmailTo>
                </Email>
              </Contact>
            </Incident>
          </IODEF-Document>
        </item>
      </publish>
    </pubsub>
  </iq>

   (The payload in the foregoing example is from [RFC7970]; payloads for
   additional use cases can be found in [RFC8274].)

   The Broker would then deliver that incident report to all Consumers
   who are subscribe to the Topic:


















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  <message
      from='broker.security-grid.example'
      to='xmpp-grid-client@mile-host.example/2EBE702A97D6'
      id='37B3921D-4F7F-450F-A589-56119A88BC2E'>
    <event xmlns='http://jabber.org/protocol/pubsub#event'>
      <items node='MILEHost'>
        <item id='iah37s61s964gquqy47aksbx9453ks77'>
          <IODEF-Document version="2.00" xml:lang="en"
            xmlns="urn:ietf:params:xml:ns:iodef-2.0"
            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation=
              "http://www.iana.org/assignments/xml-registry/
               schema/iodef-2.0.xsd">
            <Incident purpose="reporting" restriction="private">
              <IncidentID name="csirt.example.com">492382</IncidentID>
              <GenerationTime>2015-07-18T09:00:00-05:00</GenerationTime>
              <Contact type="organization" role="creator">
                <Email>
                  <EmailTo>contact@csirt.example.com</EmailTo>
                </Email>
              </Contact>
            </Incident>
          </IODEF-Document>
        </item>
      </items>
    </event>
  </message>

7.  IANA Considerations

   This document has no actions for IANA.

8.  Security Considerations

   An XMPP-Grid Controller serves as an controlling broker for XMPP-Grid
   Platforms such as Enforcement Points, Policy Servers, CMDBs, and
   Sensors, using a publish-subscribe-search model of information
   exchange and lookup.  By increasing the ability of XMPP-Grid
   Platforms to learn about and respond to security-relevant events and
   data, XMPP-Grid can improve the timeliness and utility of the
   security system.  However, this integrated security system can also
   be exploited by attackers if they can compromise it.  Therefore,
   strong security protections for XMPP-Grid are essential.

   This section provides a security analysis of the XMPP-Grid data
   transfer protocol and the architectural elements that employ it,
   specifically with respect to their use of this protocol.  Three
   subsections define the trust model (which elements are trusted to do



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   what), the threat model (attacks that can be mounted on the system),
   and the countermeasures (ways to address or mitigate the threats
   previously identified).

8.1.  Trust Model

   The first step in analyzing the security of the XMPP-Grid transport
   protocol is to describe the trust model, listing what each
   architectural element is trusted to do.  The items listed here are
   assumptions, but provisions are made in the Threat Model and
   Countermeasures sections for elements that fail to perform as they
   were trusted to do.

8.1.1.  Network

   The network used to carry XMPP-Grid messages (i.e., the underlying
   network transport layer over which XMPP runs) is trusted to:

   o  Perform best effort delivery of network traffic

   The network used to carry XMPP-Grid messages is not expected
   (trusted) to:

   o  Provide confidentiality or integrity protection for messages sent
      over it

   o  Provide timely or reliable service

8.1.2.  XMPP-Grid Platforms

   Authorized XMPP-Grid Platforms are trusted to:

   o  Preserve the confidentiality of sensitive data retrieved via the
      XMPP-Grid Controller

8.1.3.  XMPP-Grid Controller

   The XMPP-Grid Controller (including its associated Broker) is trusted
   to:

   o  Broker requests for data and enforce authorization of access to
      this data throughout its lifecycle

   o  Perform service requests in a timely and accurate manner

   o  Create and maintain accurate operational attributes





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   o  Only reveal data to and accept service requests from authorized
      parties

   The XMPP-Grid Controller is not expected (trusted) to:

   o  Verify the truth (correctness) of data

8.1.4.  Certification Authority

   The Certification Authority (CA) that issues certificates for the
   XMPP-Grid Controller and/or XMPP-Grid Platforms (or each CA, if there
   are several) is trusted to:

   o  Ensure that only proper certificates are issued and that all
      certificates are issued in accordance with the CA's policies

   o  Revoke certificates previously issued when necessary

   o  Regularly and securely distribute certificate revocation
      information

   o  Promptly detect and report any violations of this trust so that
      they can be handled

   The CA is not expected (trusted) to:

   o  Issue certificates that go beyond the XMPP-Grid needs or other
      constraints imposed by a relying party.

8.2.  Threat Model

   To secure the XMPP-Grid data transfer protocol and the architectural
   elements that implement it, this section identifies the attacks that
   can be mounted against the protocol and elements.

8.2.1.  Network Attacks

   A variety of attacks can be mounted using the network.  For the
   purposes of this subsection the phrase "network traffic" can be taken
   to mean messages and/or parts of messages.  Any of these attacks can
   be mounted by network elements, by parties who control network
   elements, and (in many cases) by parties who control network-attached
   devices.

   o  Network traffic can be passively monitored to glean information
      from any unencrypted traffic





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   o  Even if all traffic is encrypted, valuable information can be
      gained by traffic analysis (volume, timing, source and destination
      addresses, etc.)

   o  Network traffic can be modified in transit

   o  Previously transmitted network traffic can be replayed

   o  New network traffic can be added

   o  Network traffic can be blocked, perhaps selectively

   o  A "Man In The Middle" (MITM) attack can be mounted where an
      attacker interposes itself between two communicating parties and
      poses as the other end to either party or impersonates the other
      end to either or both parties

   o  Resist attacks (including denial of service and other attacks from
      XMPP-Grid Platforms)

   o  Undesired network traffic can be sent in an effort to overload an
      architectural component, thus mounting a denial of service attack

8.2.2.  XMPP-Grid Platforms

   An unauthorized XMPP-Grid Platform (one which is not recognized by
   the XMPP-Grid Controller or is recognized but not authorized to
   perform any actions) cannot mount any attacks other than those listed
   in the Network Attacks section above.

   An authorized XMPP-Grid Platform, on the other hand, can mount many
   attacks.  These attacks might occur because the XMPP-Grid Platform is
   controlled by a malicious, careless, or incompetent party (whether
   because its owner is malicious, careless, or incompetent or because
   the XMPP-Grid Platform has been compromised and is now controlled by
   a party other than its owner).  They might also occur because the
   XMPP-Grid Platform is running malicious software; because the XMPP-
   Grid Platform is running buggy software (which can fail in a state
   that floods the network with traffic); or because the XMPP-Grid
   Platform has been configured improperly.  From a security standpoint,
   it generally makes no difference why an attack is initiated.  The
   same countermeasures can be employed in any case.

   Here is a list of attacks that can be mounted by an authorized XMPP-
   Grid Platform:

   o  Cause many false alarms or otherwise overload the XMPP-Grid
      Controller or other elements in the network security system



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      (including human administrators) leading to a denial of service or
      disabling parts of the network security system

   o  Omit important actions (such as posting incriminating data),
      resulting in incorrect access

   o  Use confidential information obtained from the XMPP-Grid
      Controller to enable further attacks (such as using endpoint
      health check results to exploit vulnerable endpoints)

   o  Advertise data crafted to exploit vulnerabilities in the XMPP-Grid
      Controller or in other XMPP-Grid Platforms, with a goal of
      compromising those systems

   o  Issue a search request or set up a subscription that matches an
      enormous result, leading to resource exhaustion on the XMPP-Grid
      Controller, the publishing XMPP-Grid Platform, and/or the network

   o  Establish a communication channel using another XMPP-Grid
      Platform's session-id

   Dependencies of or vulnerabilities of authorized XMPP-Grid Platforms
   can be exploited to effect these attacks.  Another way to effect
   these attacks is to gain the ability to impersonate an XMPP-Grid
   Platform (through theft of the XMPP-Grid Platform's identity
   credentials or through other means).  Even a clock skew between the
   XMPP-Grid Platform and XMPP-Grid Controller can cause problems if the
   XMPP-Grid Platform assumes that old XMPP-Grid Platform data deserves
   to be ignored.

8.2.3.  XMPP-Grid Controllers

   An unauthorized XMPP-Grid Controller (one which is not trusted by
   XMPP-Grid Platforms) cannot mount any attacks other than those listed
   in the Network Attacks section above.

   An authorized XMPP-Grid Controller can mount many attacks.  Similar
   to the XMPP-Grid Platform case described above, these attacks might
   occur because the XMPP-Grid Controller is controlled by a malicious,
   careless, or incompetent party (either an XMPP-Grid Controller
   administrator or an attacker who has seized control of the XMPP-Grid
   Controller).  They might also occur because the XMPP-Grid Controller
   is running malicious software, because the XMPP-Grid Controller is
   running buggy software (which can fail in a state that corrupts data
   or floods the network with traffic), or because the XMPP-Grid
   Controller has been configured improperly.





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   All of the attacks listed for XMPP-Grid Platform above can be mounted
   by the XMPP-Grid Controller.  Detection of these attacks will be more
   difficult since the XMPP-Grid Controller can create false operational
   attributes and/or logs that imply some other party created any bad
   data.

   Additional XMPP-Grid Controller attacks can include:

   o  Expose different data to different XMPP-Grid Platforms to mislead
      investigators or cause inconsistent behavior

   o  Mount an even more effective denial of service attack than a
      single XMPP-Grid Platform could

   o  Obtain and cache XMPP-Grid Platform credentials so they can be
      used to impersonate XMPP-Grid Platforms even after a breach of the
      XMPP-Grid Controller is repaired

   o  Obtain and cache XMPP-Grid Controller administrator credentials so
      they can be used to regain control of the XMPP-Grid Controller
      after the breach of the XMPP-Grid Controller is repaired

   Dependencies of or vulnerabilities of the XMPP-Grid Controller can be
   exploited to obtain control of the XMPP-Grid Controller and effect
   these attacks.

8.2.4.  Certification Authority

   A Certification Authority trusted to issue certificates for the XMPP-
   Grid Controller and/or XMPP-Grid Platforms can mount several attacks:

   o  Issue certificates for unauthorized parties, enabling them to
      impersonate authorized parties such as the XMPP-Grid Controller or
      an XMPP-Grid Platform.  This can lead to all the threats that can
      be mounted by the certificate's subject.

   o  Issue certificates without following all of the CA's policies.
      Because this can result in issuing certificates that can be used
      to impersonate authorized parties, this can lead to all the
      threats that can be mounted by the certificate's subject.

   o  Fail to revoke previously issued certificates that need to be
      revoked.  This can lead to undetected impersonation of the
      certificate's subject or failure to revoke authorization of the
      subject, and therefore can lead to all of the threats that can be
      mounted by that subject.





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   o  Fail to regularly and securely distribute certificate revocation
      information.  This can cause a relying party to accept a revoked
      certificate, leading to undetected impersonation of the
      certificate's subject or failure to revoke authorization of the
      subject, and therefore can lead to all of the threats that can be
      mounted by that subject.  It can also cause a relying party to
      refuse to proceed with a transaction because timely revocation
      information is not available, even though the transaction should
      be permitted to proceed.

   o  Allow the CA's private key to be revealed to an unauthorized
      party.  This can lead to all the threats above.  Even worse, the
      actions taken with the private key will not be known to the CA.

   o  Fail to promptly detect and report errors and violations of trust
      so that relying parties can be promptly notified.  This can cause
      the threats listed earlier in this section to persist longer than
      necessary, leading to many knock-on effects.

8.3.  Countermeasures

   Below are countermeasures for specific attack scenarios to the XMPP-
   Grid infrastructure.

8.3.1.  Securing the XMPP-Grid Data Transfer Protocol

   To address network attacks, the XMPP-Grid data transfer protocol
   described in this document requires that the XMPP-Grid messages MUST
   be carried over TLS (minimally TLS 1.2 [RFC5246]) as described in
   [RFC6120] and updated by [RFC7590].  The XMPP-Grid Platform MUST
   verify the XMPP-Grid Controller's certificate and determine whether
   the XMPP-Grid Controller is trusted by this XMPP-Grid Platform before
   completing the TLS handshake.  The XMPP-Grid Controller MUST
   authenticate the XMPP-Grid Platform either using the SASL EXTERNAL
   mechanism or using the SASL SCRAM mechanism (with the SCRAM-SHA-
   256-PLUS variant being preferred over the SCRAM-SHA-256 variant and
   SHA-256 variants [RFC7677] being preferred over SHA-1 varients
   [RFC5802]).  XMPP-Grid Platforms and XMPP-Grid Controllers using
   mutual certificate-based authentication SHOULD each verify the
   revocation status of the other party's certificate.  All XMPP-Grid
   Controllers and XMPP-Grid Platforms MUST implement both SASL EXTERNAL
   and SASL SCRAM.  The selection of which XMPP-Grid Platform
   authentication technique to use in any particular deployment is left
   to the administrator.

   These protocol security measures provide protection against all the
   network attacks listed in the above document section except denial of
   service attacks.  If protection against these denial of service



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   attacks is desired, ingress filtering, rate limiting per source IP
   address, and other denial of service mitigation measures can be
   employed.  In addition, an XMPP-Grid Controller MAY automatically
   disable a misbehaving XMPP-Grid Platform.

8.3.2.  Securing XMPP-Grid Platforms

   XMPP-Grid Platforms can be deployed in locations that are susceptible
   to physical attacks.  Physical security measures can be taken to
   avoid compromise of XMPP-Grid Platforms, but these are not always
   practical or completely effective.  An alternative measure is to
   configure the XMPP-Grid Controller to provide read-only access for
   such systems.  The XMPP-Grid Controller SHOULD also include a full
   authorization model so that individual XMPP-Grid Platforms can be
   configured to have only the privileges that they need.  The XMPP-Grid
   Controller MAY provide functional templates so that the administrator
   can configure a specific XMPP-Grid Platform as a DHCP server and
   authorize only the operations and metadata types needed by a DHCP
   server to be permitted for that XMPP-Grid Platform.  These techniques
   can reduce the negative impacts of a compromised XMPP-Grid Platform
   without diminishing the utility of the overall system.

   To handle attacks within the bounds of this authorization model, the
   XMPP-Grid Controller MAY also include rate limits and alerts for
   unusual XMPP-Grid Platform behavior.  XMPP-Grid Controllers SHOULD
   make it easy to revoke an XMPP-Grid Platform's authorization when
   necessary.  Another way to detect attacks from XMPP-Grid Platforms is
   to create fake entries in the available data (honeytokens) which
   normal XMPP-Grid Platforms will not attempt to access.  The XMPP-Grid
   Controller SHOULD include auditable logs of XMPP-Grid Platform
   activities.

   To avoid compromise of XMPP-Grid Platform, XMPP-Grid Platform SHOULD
   be hardened against attack and minimized to reduce their attack
   surface.  They should be well managed to minimize vulnerabilities in
   the underlying platform and in systems upon which the XMPP-Grid
   Platform depends.  Personnel with administrative access should be
   carefully screened and monitored to detect problems as soon as
   possible.

8.3.3.  Securing XMPP-Grid Controllers

   Because of the serious consequences of XMPP-Grid Controller
   compromise, XMPP-Grid Controllers need to be especially well hardened
   against attack and minimized to reduce their attack surface.  They
   need to be well managed to minimize vulnerabilities in the underlying
   platform and in systems upon which the XMPP-Grid Controller depends.
   Network security measures such as firewalls or intrusion detection



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   systems can be used to monitor and limit traffic to and from the
   XMPP-Grid Controller.  Personnel with administrative access ought to
   be carefully screened and monitored to detect problems as soon as
   possible.  Administrators SHOULD NOT use password-based
   authentication but should instead use non-reusable credentials and
   multi-factor authentication (where available).  Physical security
   measures ought to be employed to prevent physical attacks on XMPP-
   Grid Controllers.

   To ease detection of XMPP-Grid Controller compromise should it occur,
   XMPP-Grid Controller behavior should be monitored to detect unusual
   behavior (such as a reboot, a large increase in traffic, or different
   views of an information repository for similar XMPP-Grid Platforms).
   XMPP-Grid Platforms should log and/or notify administrators when
   peculiar XMPP-Grid Controller behavior is detected.  To aid forensic
   investigation, permanent read-only audit logs of security-relevant
   information (especially administrative actions) should be maintained.
   If XMPP-Grid Controller compromise is detected, a careful analysis
   should be performed of the impact of this compromise.  Any reusable
   credentials that can have been compromised should be reissued.

8.3.4.  Broker Access Models for Topics

   The XMPP publish-subscribe specification [XEP-0060] defines five
   access models for subscribing to Topics at a Broker: open, presence,
   roster, authorize, and whitelist.  The first model allows
   uncontrolled access and the next two models are appropriate only in
   instant-messaging applications.  Therefore, a Broker SHOULD support
   only the authorize model (under which the Topic owner needs to
   approve all subscription requests and only subscribers can retrieve
   data items) and the whitelist model (under which only preconfigured
   Platforms can subscribe or retrieve data items).  In order to ease
   the deployment burden, subscription approvals and whitelist
   management can be automated (e.g, the Topic "owner" can be a policy
   server).  The choice between "authorize" and "whitelist" as the
   default access model is a matter for local service policy.

8.3.5.  Limit on Search Result Size

   While XMPP-Grid is designed for high scalability to 100,000s of
   Platforms, an XMPP-Grid Controller MAY establish a limit to the
   amount of data it is willing to return in search or subscription
   results.  This mitigates the threat of an XMPP-Grid Platform causing
   resource exhaustion by issuing a search or subscription that leads to
   an enormous result.






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8.3.6.  Securing the Certification Authority

   As noted above, compromise of a Certification Authority (CA) trusted
   to issue certificates for the XMPP-Grid Controller and/or XMPP-Grid
   Platforms is a major security breach.  Many guidelines for proper CA
   security have been developed: the CA/Browser Forum's Baseline
   Requirements, the AICPA/CICA Trust Service Principles, etc.  The CA
   operator and relying parties should agree on an appropriately
   rigorous security practices to be used.

   Even with the most rigorous security practices, a CA can be
   compromised.  If this compromise is detected quickly, relying parties
   can remove the CA from their list of trusted CAs, and other CAs can
   revoke any certificates issued to the CA.  However, CA compromise may
   go undetected for some time, and there's always the possibility that
   a CA is being operated improperly or in a manner that is not in the
   interests of the relying parties.  For this reason, relying parties
   may wish to "pin" a small number of particularly critical
   certificates (such as the certificate for the XMPP-Grid Controller).
   Once a certificate has been pinned, the relying party will not accept
   another certificate in its place unless the Administrator explicitly
   commands it to do so.  This does not mean that the relying party will
   not check the revocation status of pinned certificates.  However, the
   Administrator can still be consulted if a pinned certificate is
   revoked, since the CA and revocation process are not completely
   trusted.

8.4.  Summary

   XMPP-Grid's considerable value as a broker for security-sensitive
   data exchange distribution also makes the protocol and the network
   security elements that implement it a target for attack.  Therefore,
   strong security has been included as a basic design principle within
   the XMPP-Grid design process.

   The XMPP-Grid data transfer protocol provides strong protection
   against a variety of different attacks.  In the event that an XMPP-
   Grid Platform or XMPP-Grid Controller is compromised, the effects of
   this compromise have been reduced and limited with the recommended
   role-based authorization model and other provisions, and best
   practices for managing and protecting XMPP-Grid systems have been
   described.  Taken together, these measures should provide protection
   commensurate with the threat to XMPP-Grid systems, thus ensuring that
   they fulfill their promise as a network security clearing-house.







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9.  Privacy Considerations

   XMPP-Grid Platforms can publish information about endpoint health,
   network access, events (which can include information about what
   services an endpoint is accessing), roles and capabilities, and the
   identity of the end user operating the endpoint.  Any of this
   published information can be queried by other XMPP-Grid Platforms and
   could potentially be used to correlate network activity to a
   particular end user.

   Dynamic and static information brokered by an XMPP-Grid Controller,
   ostensibly for purposes of correlation by XMPP-Grid Platforms for
   intrusion detection, could be misused by a broader set of XMPP-Grid
   Platforms which hitherto have been performing specific roles with
   strict well-defined separation of duties.

   Care needs to be taken by deployers of XMPP-Grid to ensure that the
   information published by XMPP-Grid Platforms does not violate
   agreements with end users or local and regional laws and regulations.
   This can be accomplished either by configuring XMPP-Grid Platforms to
   not publish certain information or by restricting access to sensitive
   data to trusted XMPP-Grid Platforms.  That is, the easiest means to
   ensure privacy or protect sensitive data, is to omit or not share it
   at all.

   Another consideration for deployers is to enable end-to-end
   encryption to ensure the data is protected from the data layer to
   data layer and thus protect it from the transport layer.

10.  Operations and Management Considerations

   In order to facilitate the management of Providers and the onboarding
   of Consumers, it is helpful to generate the following ahead of time:

   o  Agreement between the operators of Provider services and the
      implementers of Consumer software regarding identifiers for common
      Topics (e.g., these could be registered with the XMPP Software
      Foundation's registry of well-known nodes for service discovery
      and publish-subscribe located at <https://xmpp.org/registrar/
      nodes.html>).

   o  Security certificates (including appropriate certificate chains)
      for Controllers, including identification of any Providers
      associated with the Controllers (which might be located at
      subdomains).

   o  Consistent and secure access control policies for publishing and
      subscribing to Topics.



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   These matters are out of scope for this document but ought to be
   addressed by the XMPP-Grid community.

11.  Acknowledgements

   The authors would like to acknowledge the contributions, authoring
   and/or editing of the following people: Joseph Salowey, Lisa
   Lorenzin, Clifford Kahn, Henk Birkholz, Jessica Fitzgerald-McKay,
   Steve Hanna, and Steve Venema.  In addition, we want to thank Takeshi
   Takahashi, Panos Kampanakis, Adam Montville, Chris Inacio, and Dave
   Cridland for reviewing and providing valuable comments.

12.  References

12.1.  Normative References

   [I-D.ietf-sacm-terminology]
              Birkholz, H., Lu, J., Strassner, J., and N. Cam-Winget,
              "Secure Automation and Continuous Monitoring (SACM)
              Terminology", draft-ietf-sacm-terminology-14 (work in
              progress), December 2017.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC6120]  Saint-Andre, P., "Extensible Messaging and Presence
              Protocol (XMPP): Core", RFC 6120, DOI 10.17487/RFC6120,
              March 2011, <https://www.rfc-editor.org/info/rfc6120>.

   [RFC7590]  Saint-Andre, P. and T. Alkemade, "Use of Transport Layer
              Security (TLS) in the Extensible Messaging and Presence
              Protocol (XMPP)", RFC 7590, DOI 10.17487/RFC7590, June
              2015, <https://www.rfc-editor.org/info/rfc7590>.

   [RFC7677]  Hansen, T., "SCRAM-SHA-256 and SCRAM-SHA-256-PLUS Simple
              Authentication and Security Layer (SASL) Mechanisms",
              RFC 7677, DOI 10.17487/RFC7677, November 2015,
              <https://www.rfc-editor.org/info/rfc7677>.

   [XEP-0004]
              Eatmon, R., Hildebrand, J., Miller, J., Muldowney, T., and
              P. Saint-Andre, "Data Forms", XSF XEP 0004, August 2007.

   [XEP-0030]
              Hildebrand, J., Millard, P., Eatmon, R., and P. Saint-
              Andre, "Service Discovery", XSF XEP 0030, July 2010.



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   [XEP-0060]
              Millard, P., Saint-Andre, P., and R. Meijer, "Publish-
              Subscribe", XSF XEP 0060, December 2017.

12.2.  Informative References

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <https://www.rfc-editor.org/info/rfc5246>.

   [RFC5802]  Newman, C., Menon-Sen, A., Melnikov, A., and N. Williams,
              "Salted Challenge Response Authentication Mechanism
              (SCRAM) SASL and GSS-API Mechanisms", RFC 5802,
              DOI 10.17487/RFC5802, July 2010,
              <https://www.rfc-editor.org/info/rfc5802>.

   [RFC7970]  Danyliw, R., "The Incident Object Description Exchange
              Format Version 2", RFC 7970, DOI 10.17487/RFC7970,
              November 2016, <https://www.rfc-editor.org/info/rfc7970>.

   [RFC8274]  Kampanakis, P. and M. Suzuki, "Incident Object Description
              Exchange Format Usage Guidance", RFC 8274,
              DOI 10.17487/RFC8274, November 2017,
              <https://www.rfc-editor.org/info/rfc8274>.

Authors' Addresses

   Nancy Cam-Winget (editor)
   Cisco Systems
   3550 Cisco Way
   San Jose, CA  95134
   USA

   Email: ncamwing@cisco.com


   Syam Appala
   Cisco Systems
   3550 Cisco Way
   San Jose, CA  95134
   USA

   Email: syam1@cisco.com







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   Scott Pope
   Cisco Systems
   5400 Meadows Road
   Suite 300
   Lake Oswego, OR  97035
   USA

   Email: scottp@cisco.com


   Peter Saint-Andre
   Mozilla

   Email: stpeter@mozilla.com





































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