MILE N. Cam-Winget, Ed.
Internet-Draft S. Appala
Intended status: Standards Track S. Pope
Expires: December 28, 2018 Cisco Systems
P. Saint-Andre
Mozilla
June 26, 2018
Using XMPP for Security Information Exchange
draft-ietf-mile-xmpp-grid-06
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
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This Internet-Draft will expire on December 28, 2018.
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
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include Simplified BSD License text as described in Section 4.e of
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 4
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].
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 is those who implement and
deploy security reporting systems, in general the SACM terms are used
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(however, mappings are provided for the benefit of XMPP developers
and operators).
Broker: In SACM, a specific type of controller containing control
plane functions; as used here, the term refers to an XMPP publish-
subscribe service.
Broker Flow: In SACM, 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: In SACM, an entity that contains functions to receive
information from other components; as used here, the term refers
to an XMPP publish-subscribe Subscriber.
Controller: In SACM, 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: In SACM, an entity that contains functions to provide
information to other components; as used here, the term refers to
an XMPP publish-subscribe Publisher.
Publisher: The XMPP term for a Provider.
Publish-Subscribe Service: The XMPP term for the kind Broker
discussed here.
Subscriber: The XMPP term for a Consumer.
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) 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].
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3. Architecture
The following figure illustrates the architecture of XMPP-Grid.
+--------------------------------------+
| +--------------------------------------+
| | +--------------------------------------+
| | | |
+-| | 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 and relationships (e.g.,
Provider or Consumer) 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 thru the
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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 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 (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 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 (Topics) to be
published or consumes.
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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