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

MILE                                                  N. Cam-Winget, Ed.
Internet-Draft                                                 S. Appala
Intended status: Standards Track                                 S. Pope
Expires: May 3, 2018                                       Cisco Systems
                                                          P. Saint-Andre
                                                              Jabber.org
                                                        October 30, 2017


              Using XMPP for Security Information Exchange
                      draft-ietf-mile-xmpp-grid-04

Abstract

   This document describes how to use the Extensible Messaging and
   Presence Protocol (XMPP) as a transport for collecting and
   distributing 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 http://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 May 3, 2018.

Copyright Notice

   Copyright (c) 2017 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
   (http://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



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   to this document.  Code Components extracted from this document must
   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 . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Architecture  . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Workflow  . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Service Discovery . . . . . . . . . . . . . . . . . . . . . .   6
   6.  IODEF Example . . . . . . . . . . . . . . . . . . . . . . . .   7
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
     8.1.  Trust Model . . . . . . . . . . . . . . . . . . . . . . .   9
       8.1.1.  Network . . . . . . . . . . . . . . . . . . . . . . .  10
       8.1.2.  XMPP-Grid Platforms . . . . . . . . . . . . . . . . .  10
       8.1.3.  XMPP-Grid Controller  . . . . . . . . . . . . . . . .  10
       8.1.4.  Certification Authority . . . . . . . . . . . . . . .  10
     8.2.  Threat Model  . . . . . . . . . . . . . . . . . . . . . .  11
       8.2.1.  Network Attacks . . . . . . . . . . . . . . . . . . .  11
       8.2.2.  XMPP-Grid Platforms . . . . . . . . . . . . . . . . .  12
       8.2.3.  XMPP-Grid Controllers . . . . . . . . . . . . . . . .  13
       8.2.4.  Certification Authority . . . . . . . . . . . . . . .  14
     8.3.  Countermeasures . . . . . . . . . . . . . . . . . . . . .  15
       8.3.1.  Securing the XMPP-Grid Transport Protocol . . . . . .  15
       8.3.2.  Securing XMPP-Grid Platforms  . . . . . . . . . . . .  16
       8.3.3.  Securing XMPP-Grid Controllers  . . . . . . . . . . .  16
       8.3.4.  Limit on search result size . . . . . . . . . . . . .  17
       8.3.5.  Cryptographically random session-id and
               authentication checks for ARC . . . . . . . . . . . .  17
       8.3.6.  Securing the Certification Authority  . . . . . . . .  18
     8.4.  Summary . . . . . . . . . . . . . . . . . . . . . . . . .  18
   9.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  19
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  19
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  19
     11.2.  Informative References . . . . . . . . . . . . . . . . .  20
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  20

1.  Introduction

   This document describes "XMPP-Grid": a method for using the
   Extensible Messaging and Presence Protocol (XMPP) [RFC6120] as a
   transport for collecting and distributing security-relevant
   information among network platforms, endpoints, and any other
   network-connected device.  Among other services, XMPP provides a



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   publish-subscribe service that acts as a broker, providing 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 uses the
   Incident Object Description Exchange Format (IODEF) [RFC7970] to
   illustrate the principles of XMPP-Grid.

2.  Terminology

   This document uses XMPP terminology defined in [RFC6120] and
   [XEP-0060] as well as Security Automation and Continuous Monitoring
   (SACM) terminology defined in [I-D.ietf-sacm-terminology].  Because
   the intended audience for this document consists of those who
   implement and deploy security reporting systems, in general the SACM
   terms are used here (however, mappings are provided for the benefit
   of XMPP developers and operators).

   Broker:  As defined in [I-D.ietf-sacm-terminology], a Broker is 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 Subscribers and
      Publishers to Topics, receives messages from Publishers, and
      delivers published messages to Subscribers.

   Consumer:  As defined in [I-D.ietf-sacm-terminology], a Consumer is a
      component that contains functions to receive information from
      other components; as used here, the term refers to an XMPP
      publish-subscribe Subscriber.

   Controller:  As defined in [I-D.ietf-sacm-terminology], a controller
      is a "component containing control plane functions that manage and
      facilitate information sharing or execute on security functions";
      as used here, the term refers to either an XMPP server, which
      provides both core message delivery [RFC6120] used by publish-
      subscribe entities.

   Node:  The term used in the XMPP publish-subscribe specification
      [XEP-0060] for a Topic.

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

   Provider:  As defined in [I-D.ietf-sacm-terminology], a Provider is a
      component that contains functions to provide information to other




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      components; as used here, the term refers to an XMPP publish-
      subscribe Publisher.

   Publisher:  The term used in the XMPP publish-subscribe specification
      [XEP-0060] for a Provider.

   Publish-Subscribe Service:  A Broker that implements the XMPP
      publish-subscribe extension [XEP-0060].

   Subscriber:  The term used in the XMPP publish-subscribe
      specification [XEP-0060] for a Consumer.

   Topic:  A contextual information channel created on a Broker at which
      messages generated by a Publisher will be propagated by XMPP in
      real time to one or more Subscribers.  Each Topic is limited to a
      type and format of security data (e.g., IODEF) that a platform
      wants to share with other platform(s) and a specified 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
   and then establish appropriate authorizations and relationships
   (e.g., Publisher or Subscriber) at the Broker (XMPP publish-subscribe
   service).  The control plane messaging is established through XMPP
   and shown as "A" (control plane interface) in Figure 1.  Authorized
   nodes may then share data either thru 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
   (although "direct flow" interactions can be used for specialized



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   purposes such as bulk data transfer, 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 (XMPP server).

   b.  The Controller authenticates the Platform.

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

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

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

   f.  Any Platform on the Grid may subscribe to any Topics published to
       the Grid (as permitted by authorization policy), and (as
       Subscribers) will then receive a continuous, real-time stream of
       updates from the Topics to which they are subscribed.

5.  Service Discovery

   Using the XMPP service discovery extension [XEP-0030], a Controller
   enables Platforms to discover what information may be consumed
   through the Broker (publish-subscribe service).  For instance, the
   Controller might provide a Broker at 'broker.security-grid.example',
   where 'security-grid.example' is the Controller host.  Below is an
   example for how a Platform can query for available information from
   the XMPP-Controller:

   <iq type='get'
       from='xmpp-grid-client@mile-host.example/postures'
       to='broker.security-grid.example'
       id='disco1'>
     <query xmlns='http://jabber.org/protocol/disco#items'/>
   </iq>

   The XMPP-Controller responds with the different types of information
   it can publish:



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   <iq type='result'
       from='broker.security-grid.example'
       to='xmpp-grid-client@mile-host.example/postures'
       id='disco1'>
     <query xmlns='http://jabber.org/protocol/disco#items'
            node='secinfo'>
       <item node='NEA1'
             name='endpoint-posture'
             jid='broker.security-grid.example'/>
       <item node='MILEHost'
             name='iodef-1.0'
             jid='broker.security-grid.example'/>
     </query>
   </iq>

6.  IODEF Example

   A Platform follows the standard XMPP workflow for connecting to the
   Controller as well as using the XMPP discovery mechanisms to discover
   the availability to consume IODEF information.  The general workflow
   is summarized in the figure below:






























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+----------------+         +----------------+         +----------------+
| IODEF Client   |         | XMPP Server    |         | IODEF Service  |
|  (Subscriber)  |         | (Controller)   |         |  (Publisher)   |
+----------------+         +----------------+         +----------------+
        |                          |                         |
        |     IODEF Client         |                         |
        |     Authentication       |                         |
        |<------------------------>|                         |
        |                          | IODEF Service           |
        |                          | Authentication          |
        |                          |<----------------------->|
        |                          | Create IODEF as a Topic |
        |                          | (XEP-0060)              |
        |                          |<------------------------|
        |                          | Topic Creation Success  |
        |                          |------------------------>|
        | Topic Discovery          |                         |
        | (XEP-0030)               |                         |
        |------------------------->|                         |
        | Discovery Response       |                         |
        | with Topics              |                         |
        |<-------------------------|                         |
        |                          |                         |
        | Subscribe to IODEF Topic |                         |
        | (XEP-0060)               |                         |
        |------------------------->|                         |
        | Subscription Success     |                         |
        |<-------------------------|                         |
        |                          | IODEF Incident Publish  |
        | IODEF Incident Publish   |<------------------------|
        |<-------------------------|                         |
        |                          |                         |

                     Figure 2: IODEF Example Workflow

   An example XMPP discovery request for an IODEF 1.0 topic is shown
   below:

   <iq type='get'
       from='iodefclientabc@company.example'
       to='pubsub.company.example'
       id='nodes1'>
     <query xmlns='http://jabber.org/protocol/disco#items'/>
   </iq>

   An example XMPP discovery response for an IODEF 1.0 topic is shown
   below:




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   <iq type='result'
       from='pubsub.company.example'
       to='iodefclientabc@company.example'
       id='nodes1'>
     <query xmlns='http://jabber.org/protocol/disco#items'>
       <item jid='pubsub.company.example'
             node='incident'
             name='IODEF incident report'/>
     </query>
   </iq>

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 transport
   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 what), the threat
   model (attacks that may 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.








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8.1.1.  Network

   The network used to carry XMPP-Grid messages 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 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

   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




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   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 transport 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" should be
   taken to mean messages and/or parts of messages.  Any of these
   attacks may 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 may be passively monitored to glean information
      from any unencrypted traffic

   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 may be modified in transit

   o  Previously transmitted network traffic may be replayed

   o  New network traffic may be added

   o  Network traffic may be blocked, perhaps selectively

   o  A "Man In The Middle" (MITM) attack may 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




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

   o  Undesired network traffic may 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 Platforms (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 may 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 may 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
      (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



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

   Dependencies of or vulnerabilities of authorized XMPP-Grid Platforms
   may 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 should 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 may fail in a state that corrupts data
   or floods the network with traffic), or because the XMPP-Grid
   Controller has been configured improperly.

   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 may 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





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   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 may 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 may 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.

   o  Fail to regularly and securely distribute certificate revocation
      information.  This may 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.




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8.3.  Countermeasures

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

8.3.1.  Securing the XMPP-Grid Transport Protocol

   To address network attacks, the XMPP-Grid transport 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 mutual certificate-
   based authentication in the TLS handshake or using Basic
   Authentication as described in IETF RFC 2617.  XMPP-Grid Controller
   MUST use Simple Authentication and Security Layer (SASL), described
   in [RFC4422], to support the aforesaid authentication mechanisms.
   SASL offers authentication mechanism negotiations between the XMPP-
   Grid Controller and XMPP-Grid node during the connection
   establishment phase.  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 mutual
   certificate-based authentication and Basic Authentication.  The
   selection of which XMPP-Grid Platform authentication technique to use
   in any particular deployment is left to the administrator.

   An XMPP-Grid Controller MAY also support a local, configurable set of
   Basic Authentication userid-password pairs.  If so, it is
   implementation dependent whether an XMPP-Grid Controller ends a
   session when an administrator changes the configured password.  Since
   Basic Authentication has many security disadvantages (especially the
   transmission of reusable XMPP-Grid Platform passwords to the XMPP-
   Grid Controller), it SHOULD only be used when absolutely necessary.
   Per the HTTP specification, when basic authentication is in use, an
   XMPP-Grid Controller MAY respond to any request that lacks
   credentials with an error code similar to HTTP code 401.  An XMPP-
   Grid Platform SHOULD avoid this code by submitting basic auth
   credentials with every request when basic authentication is in use.
   If it does not do so, an XMPP-Grid Platform MUST respond to this code
   by resubmitting the same request with credentials (unless the XMPP-
   Grid Platform is shutting down).

   Best practices for the use of TLS in XMPP are defined in [RFC7590].





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   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
   attacks is desired, ingress filtering, rate limiting per source IP
   address, and other denial of service mitigation measures may 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 may be deployed in locations that are susceptible
   to physical attacks.  Physical security measures may be taken to
   avoid compromise of XMPP-Grid Platforms, but these may not always be
   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 may 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 SHOULD be especially well hardened
   against attack and minimized to reduce their attack surface.  They



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   should 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
   systems may be used to monitor and limit traffic to and from the
   XMPP-Grid Controller.  Personnel with administrative access should 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 SHOULD 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 may have been compromised should be reissued.

8.3.4.  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.

8.3.5.  Cryptographically random session-id and authentication checks
        for ARC

   An XMPP-Grid Controller SHOULD ensure that the XMPP-Grid Platform
   establishing an Authenticated Results Chain (ARC) is the same XMPP-
   Grid Platform as the XMPP-Grid Platform that established the
   corresponding Synchronization Source Identifier (SSRC).  The XMPP-
   Grid Controller SHOULD employ both of the following strategies:

   o  session-ids SHOULD be cryptographically random

   o  The HTTPS transport for the SSRC and the ARC SHOULD be
      authenticated using the same credentials.  SSL session resumption
      MAY be used to establish the ARC based on the SSRC SSL session.




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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 may 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 may 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 transport 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 may publish information about endpoint health,
   network access, events (which may 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 may 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 should 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.  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.

11.  References

11.1.  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-13 (work in
              progress), July 2017.




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   [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>.

   [RFC4422]  Melnikov, A., Ed. and K. Zeilenga, Ed., "Simple
              Authentication and Security Layer (SASL)", RFC 4422,
              DOI 10.17487/RFC4422, June 2006, <https://www.rfc-
              editor.org/info/rfc4422>.

   [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>.

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

   [XEP-0060]
              Millard, P. and P. Saint-Andre, "Publish-Subscribe",
              XSF XEP 0060, December 2016.

11.2.  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>.

   [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>.

Authors' Addresses

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

   Email: ncamwing@cisco.com




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

   Email: syam1@cisco.com


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

   Email: scottp@cisco.com


   Peter Saint-Andre
   Jabber.org
   P.O. Box 787
   Parker, CO  80134
   USA

   Email: stpeter@jabber.org

























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