NEA Working Group P. Sangster
Internet Draft Symantec
Expires: Sept 2007 H. Khosravi
Intel
M. Mani
Avaya
K. Narayan
Cisco Systems
J. Tardo
Nevis Networks
March 2007
Requirements for
Network Endpoint Assessment (NEA)
draft-ietf-nea-requirements-01.txt
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Abstract
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This document defines the problem statement, scope and interface
(protocol) requirements between the components of the NEA (Network
Endpoint Assessment) reference model. NEA provides owners of
networks (e.g. an enterprise offering remote access) a mechanism to
evaluate the posture of a system. This may take place during the
request for network access and/or subsequently at any time while
connected to the network. The learned posture information can then
be applied to a variety of compliance oriented decisions. The
posture information is frequently useful for detecting systems that
are lacking (or have out of date) security protective mechanisms
(e.g. anti-virus, firewall).
In order to provide context for the requirements, a reference
model and terminology are introduced. This model is provided for
informational purposes but is based on the models used by NAC
[CNAC], NAP[NAP] and TNC[TNC].
Table of Contents
1. Introduction....................................................3
1.1 Conventions Used in This Document............................4
2. Terminology.....................................................5
3. Applicability...................................................7
3.1 Scope........................................................7
3.2 Applicability of Environments................................8
4. Problem Statement...............................................9
5. Reference Model................................................10
5.1 Components..................................................11
5.1.1 NEA Client.............................................11
5.1.2 NEA Server.............................................14
5.2 Protocols...................................................17
5.2.1 Posture Attribute Protocol (PA)........................17
5.2.2 Posture Broker Protocol (PB)...........................18
5.2.3 Posture Transport Protocol (PT)........................18
5.3 Attributes..................................................18
5.3.1 Attributes Normally Sent by NEA Client:................19
5.3.2 Attributes Normally Sent by NEA Server:................19
6. Use Cases......................................................20
6.1 Initial Assessment..........................................21
6.1.1 Triggered by Network Connection Request................21
6.1.2 Triggered by Request for Network Service...............23
6.1.3 Triggered by Endpoint..................................26
6.2 Posture Re-Assessment.......................................28
6.2.1 Triggered by NEA Client................................29
6.2.2 Triggered by NEA Server................................31
7. Requirements...................................................34
7.1 Common Protocol Requirements................................34
7.2 Posture Attribute (PA) Protocol Requirements................35
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7.3 Posture Broker (PB) Protocol Requirements...................37
7.4 Posture Transport (PT) Protocol Requirements................38
8. Security Considerations........................................39
8.1 Trust.......................................................39
8.1.1 Endpoint Components....................................40
8.1.2 Network Communications.................................41
8.1.3 NEA Server Components..................................42
8.2 Protection Mechanisms at Multiple Layers....................42
8.3 Relevant Classes of Attack..................................43
8.3.1 Man-in-the-Middle (MITM)...............................44
8.3.2 Message Modification...................................44
8.3.3 Message Replay or Attribute Theft......................45
8.3.4 Other Types of Attack..................................45
9. Privacy Considerations.........................................46
9.1 Implementer Considerations..................................47
9.2 Minimizing Attribute Disclosure.............................48
10. References....................................................50
10.1 Normative References.......................................50
10.2 Informative References.....................................51
Acknowledgments...................................................51
Authors' Addresses................................................51
1. Introduction
Today, most network providers can leverage existing standards-
based technologies to restrict access to their network based
upon criteria such as the requesting system's user or host-based
identity, source IP address or physical access point. However
these approaches still leave the network vulnerable to malware-
based attack, when an authorized but infected system is admitted
and the malware is able to spread throughout the internal
network.
As a result, network operators need a proactive mechanism to
assess the state of systems joining or present on the network to
determine their status relative to network compliance policies.
For example, if a system is determined to be out of compliance
because it is lacking proper defensive mechanisms such as
firewalls, anti-virus software or the absence of critical
security patches, there needs to be a way to safely repair
(remediate) the system so that it can be subsequently trusted to
join and operate on the network. The NEA technology strives to
provide a mechanism to report the configuration of an endpoint
for evaluation against network compliance policy. Such a
mechanism could offer a useful tool for the network operators'
arsenal but should be recognized as not being a complete
Endpoint compliance solution in and of itself.
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Network Endpoint Assessment (NEA) architectures have been
implemented in the industry allowing the network to have
visibility into the configuration of the system (e.g. security
Posture). These can evaluate compliance when the system requests
access to the network or at any time while the system is
connected to the network, enabling that system's compliance
status to be factored into various admission and access control
decisions. NEA typically involves the use of special client
software running on the requesting system that observes and
reports on the configuration of the system to the network
infrastructure. The infrastructure has corresponding validation
software that is capable of comparing the system configuration
information with network compliance policy and providing the
result to appropriate authorization entities that make decisions
about network and application access.
In many cases, the admission decision is provisioned to the
enforcement mechanisms on the network and/or system requesting
access. The decision might allow for no access, limited access
(possibly to allow for remediation), or full access to the
network. While the NEA Working Group recognizes there is a link
between an assessment and the enforcement of the assessment
decision, the mechanisms and protocols for enforcement are not
in scope for this specification.
Architectures, similar to NEA, have existed in the industry for
some time and are present in shipping products, but do not offer
interoperability. Some examples of such architectures include:
Trusted Computing Group's TNC [TNC], Microsoft's NAP [NAP],
Cisco's NAC [CNAC]). These technologies assess the software or
hardware configuration of endpoint devices for the purposes of
monitoring or enforcing compliance to an organization's policy
at the time of access to the network. These architectures are
not interoperable since most of the technologies used to
implement the architecture are proprietary and not standards.
The NEA working group is working on defining standard protocols
so as to enable interoperability between devices from different
vendors allowing network owners to deploy truly heterogeneous
solutions. This document describes the requirements for NEA
candidate technologies and protocols.
1.1 Conventions Used in This Document
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 [KEYWORDS].
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2. Terminology
This section defines a set of terms used throughout this
document. In some cases these terms have been used in other
contexts with different meanings so this section attempts to
describe each term's meaning with respect to the NEA WG
activities.
Assessment - The process of collecting Posture from a set of
Endpoint Components such that the appropriate validators may
evaluate the Posture against compliance policy.
Assertion Attributes - Class of Attribute including re-usable
information about the success of a prior Assessment of the
Endpoint. This could be used to optimize subsequent
Assessments by avoiding a full Posture re-Assessment. For
example, this type of Attribute might be issued specifically
to a particular Endpoint, dated and signed by the NEA Server
allowing that Endpoint to re-use it for a time period to
assert compliance to a set of policies. The NEA Server might
accept this in lieu of obtaining Posture information.
Attribute - Data element including any requisite meta-data
describing an observed, expected or status of a Component
property. NEA recognizes a variety of classes of Attributes
particular to their usage: Assertion Attributes, Compliance
Claim Attributes, Posture Attributes, Policy Attributes,
Request Attributes, Result Attributes, and Remediation
Attributes. Within each class, there are two different types
of Attributes: standard and vendor-specific. The standard
attributes will be standardized by the NEA WG.
Compliance Claim Attribute - Class of Attribute used by an NEA
Client to claim that the Endpoint complies with a particular
policy. For example, these Attributes are used when the NEA
Client is offered Policy Attributes and wishes to claim
compliance with the Policy rather then provide Posture
Attributes to show compliance.
Component - Software, hardware or firmware entity performing a
particular logical function on the Endpoint. For example, a
component may be a Posture Collector designed to ascertain
the Posture of another Component such as a particular vendor
product (e.g. Norton Anti-Virus) running on the Endpoint.
Deployer - Role of an entity that makes available for use
hardware and/or software solutions. For example, an
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administrator within an enterprise IT department might
release an NEA Server for use on its network.
Dialog - Sequence of request/response Messages exchanged
Endpoint - Any host computing device that can be connected to a
network. This includes: laptops, desktops, servers, cell
phone or any device with an IP address.
Message - Self contained unit of communication between
Components. For example, a PA Message might carry a set of
Posture Attributes from a Posture Collector to a Posture
Validator.
Owner - the role of an entity who is the legal, rightful
possessor on an asset (e.g. Endpoint). The owner is entitled
to maintain control over the policies enforced on the device
even if the asset is not within the Owner's possession. The
Owner may permit User override or augmentation of control
policies or may not assert any policies limiting use of
asset.
Policy Attributes - Class of Attribute sent by an NEA Server
describing (or referencing) the desired policy to be met by a
set of Components on the Endpoint. For example, Policy
Attributes might be used to enable an NEA Client to determine
whether the Endpoint is compliant without disclosing Posture
information. Instead, the NEA Client makes claims of
compliance to policy in Compliance Claim Attributes.
Posture - Configuration and/or status of hardware or software
Component(s) on an Endpoint as it pertains to an
organization's security policy.
Posture Attributes - Class of Attribute describing a quality or
characteristic of a Component. For example, a Posture
Attribute might describe the version of a Component installed
on the system. Posture Attributes are normally created by a
Posture Collector for inclusion in a Posture description of
an Endpoint.
Request Attributes - Class of Attribute containing the list of
Attributes the NEA Client is requested to send to the NEA
Server.
Remediation Attributes - Class of Attribute including the
remediation instructions for how to bring an endpoint into
compliance with one or more policies.
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Result Attributes - Class of Attribute describing whether the
Endpoint is in compliance with NEA policy. The Result
Attribute is created by the NEA Server normally at the
conclusion of the Assessment to indicate whether the Endpoint
was considered compliant or not. Multiple of these
Attributes may be used allowing for Posture Validator level
decisions to be communicated in addition to an overall,
global posture decision from the Posture Broker Server.
Session - Stateful connection (e.g. PB protocol described in
Section 3) capable of carrying one or more Messages from
multiple subscribed Posture Collectors and Validators.
User - Role of an entity that is making use of the services of
an Endpoint. The User may not own the Endpoint so might need
to operate within the acceptable use constraints defined by
the Endpoint's Owner. For example, an enterprise employee
might be a User of a computer provided by the enterprise
(Owner) to perform her job.
3. Applicability
This section discusses the scope of technologies being
standardized and the network environments where it is envisioned
that the NEA technologies might be applicable.
3.1 Scope
The priority of the NEA working group is to develop standard
protocols at the higher layers in the Reference Model (see
section 5): the Posture Attribute protocol (PA) and the Posture
Broker protocol (PB). PA and PB will be designed to be carried
over a variety of lower layer transport (PT) protocols. When
used with standard lower layer protocols, the PA and PB
protocols are intended to allow interoperability between an NEA
Client from one vendor and an NEA Server from another. This
specification will not focus on the interfaces between NEA
Reference Model Components nor requirements their internals.
Any discussion of these aspects is provided to provide context
for understanding the model and resulting requirements.
Some tangent areas not shown in the Reference Model that are
also out of scope for the NEA working group, and thus this
specification, include:
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o Standardizing the protocols and mechanisms for enforcing
restricted network access,
o Developing standard protocols for remediation of non-
compliant Endpoints,
o Detecting or handling lying Endpoints (see section 8.1.1
for more information).
3.2 Applicability of Environments
Because the NEA model is based on special software being present
on the Endpoint and in the network infrastructure and the nature
of the information being exposed, the use of NEA technologies
may not apply in a variety of situations possible on the
Internet. Therefore, this section discusses some of the
scenarios where NEA is most likely to be applicable and some
where it may not. Ultimately, the use of NEA within a
deployment is not restricted to just these scenarios. The
decision of whether to use NEA technologies lies in the hands of
the Deployer (e.g. network provider) based upon the expected
relationship they have with the Owners and Users of potential
Endpoints.
NEA technologies are largely focused on scenarios where the
Owner of the Endpoint is the same as the Owner of the Network.
This is a very common model for enterprises which provide
equipment to employees to perform their duties. These employees
are likely bound under an employment contract which outlines
what level of visibility the employer expects to have into the
employee's use of company assets and possibly activities during
work hours. This contract may establish the expectation that
the Endpoint needs to conform to policies set forth by the
enterprise.
Some other environments may be in a similar situation and thus
find NEA technologies to be beneficial. For example,
environments where the Endpoint is owned by a party (possibly
even the User) which has explicitly expressed a desire to
conform to the policies established by a network or service
provider in exchange for being able to access its resources. An
example of this might be an independent contractor with a
personal laptop, working for a company imposing NEA assessment
policies on its employees, who may wish a similar level of
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access and is willing to conform to its policies. NEA
technologies may be applicable to this situation.
Conversely, some environments where NEA is not expected to be
applicable would be environments where the Endpoint is owned by
a User that has not agreed to conform to a network provider's
policies. An example might include when the above contractor
visits any public area like the local coffee shop which offers
Internet access. This coffee shop would not be expected to be
able to use NEA technologies to assess the Posture of the
contractor's laptop. Because of the potentially invasive nature
of NEA technology, such an assessment could amount to an
invasion of privacy of the contractor.
Other environments are more difficult to determine whether NEA
is applicable, so the NEA WG will consider them to be out of
scope for consideration and specification. In order for an
environment to be considered applicable for NEA, the Owner or
User of an Endpoint must have established a clear expectation
that it will comply with the policies of the Owner and operator
of the network. Such an expectation likely includes a
willingness to disclose appropriate information necessary for
the network to perform compliance checks.
4. Problem Statement
NEA technology may be used for several purposes. One use is to
facilitate Endpoint compliance checking against an
organization's security policy when an Endpoint connects to the
network. Organizations often require Endpoints to run an IT-
specified OS configuration and have certain security
applications enabled, e.g. anti-virus software, host intrusion
detection/prevention systems, personal firewalls, and patch
management software. An Endpoint that is not compliant with IT
policy may be vulnerable to a number of known threats that might
exist on the network.
Without NEA technology, ensuring compliance of Endpoints to
corporate policy is a time-consuming and difficult task. Not all
Endpoints are managed by a corporation's IT organization, e.g.
lab assets and guest machines. Even for assets that are
managed, they may not receive updates in a timely fashion
because they are not permanently attached to the corporate
network, e.g. laptops. With NEA technology, the network is able
to assess an Endpoint as soon as it requests access to the
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network or at any time after joining the network. This provides
the corporation an opportunity to check compliance of all NEA-
capable Endpoints in a timely fashion and facilitate Endpoint
remediation where needed.
The decision of how to handle non-compliant Endpoints can be
made by the network administrator impossibly based on
information from other security mechanisms on the network (e.g.
authentication). For example, remediation instructions or
warnings may be sent to the endpoint. Also, network access
technologies can use the NEA Assessment results to restrict or
deny access to an Endpoint, while allowing vulnerabilities to be
addressed before an Endpoint is exposed to attack. The
communication and representation of NEA Assessment results to
network access technologies on the network is out-of-scope for
this document.
Re-assessment is an important part of NEA technology as it
allows for additional Assessments of previously considered
compliant Endpoints to be performed. This might become
necessary because network compliance policies and/or Endpoint
Posture can change over time. A system initially assessed as
being compliant when it joined the network may no longer be in
compliance after changes occur. For example, re-assessment
might be necessary if a User disables a security protection
(e.g. host firewall) required by policy or when the firewall
becomes non-compliant after a firewall patch is issued and
network policy is changed to require the patch.
Another use of NEA technology may be to verify or supplement
organization asset information stored in inventory databases.
NEA technology can be used to address the above problem covering
a range of ways of connecting to the network including (but not
limited to) wired and wireless LAN access, remote access via
IPsec[IPSEC] or SSL[TLS] VPN, or gateway access. NEA technology
can also be used to check and report compliance for Endpoints when
they try to access certain mission critical applications within an
enterprise by employing application triggered Assessment.
5. Reference Model
This section describes the Reference Model for Network Endpoint
Assessment. This model is provided to establish a context for the
discussion of requirements and may not directly map to any
particular product or deployment architecture. The model includes
the major Components of the NEA Client and Server and their
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relationships, as well as the protocols they use to communicate at
various levels (e.g. PA is carried by the PB protocol). The
vertical lines in the model represent APIs and/or protocols between
Components within the NEA Client or Server. These interfaces are
out of scope for standardization in the NEA WG.
+-------------+ +--------------+
| Posture | <--------PA--------> | Posture |
| Collectors | | Validators |
| (1 .. N) | | (1 .. N) |
+-------------+ +--------------+
| |
| |
| |
+-------------+ +--------------+
| Posture | | Posture |
| Broker | <--------PB--------> | Broker |
| Client | | Server |
+-------------+ +--------------+
| |
| |
+-------------+ +--------------+
| Posture | | Posture |
| Transport | <--------PT--------> | Transport |
| Client | | Server |
| (1 .. N) | | (1 .. N) |
+-------------+ +--------------+
NEA CLIENT NEA SERVER
Figure 1: NEA Reference Model
The NEA Reference model does not include any mechanisms for
discovery of NEA Clients and NEA Servers. It is expected that NEA
Clients and NEA Servers are configured with information that allow
them to reach each other. The specific methods of referencing the
configuration and establishing the communication channel are out of
scope for the NEA Reference Model and should be covered part of the
specifications of candidate protocols for the Posture Transport.
5.1 Components
5.1.1 NEA Client
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The NEA Client is resident on an Endpoint device and comprises
of the following components:
o Posture Collector
o Posture Broker Client
o Posture Transport Client
5.1.1.1 Posture Collector
The Posture Collector is the Component that is responsible for
responding to requests for Posture information from the Posture
Broker Client and receiving Posture Assessment requests in
Request Attributes, Policy information in Policy Attributes,
Assessment decisions in Result Attributes and remediation
instructions (Remediation Attributes). A single NEA Client can
have several Posture Collectors capable of collecting standard
and/or vendor-specific Posture Attributes for particular
Endpoint Components. Typical examples include Posture Collectors
that provide information about Operating System (OS) patch
levels, anti-virus software, and security applications on the
Endpoint such as host firewall or an IDS. Posture Collectors may
also be capable of evaluating rules and asserting Posture
decisions.
Each Posture Collector will be associated with an identifier
that enables it to be the specified as the destination in a PA
Message. The Posture Broker Client uses this identifier to
route Messages to this collector. This identifier might be
dynamic (e.g. assigned by the Posture Broker Client upon
registration) or more static (e.g. provided during registration)
or a function of the Attribute Messages the collector desires to
receive (e.g. Message type subscription).
The NEA model allocates the following responsibilities to the
Posture Collector Component:
o Consulting with local privacy and security policies that
may restrict what information is allowed to be disclosed to
a given NEA Server.
o Receiving Request Attributes from a Posture Validator and
performing the local processing required to respond
appropriately. This may include:
- Collecting associated Posture information for the
Component(s) on the Endpoint and returning this
information in Posture Attributes.
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- Recognizing a recently issued (cached) Assertion
Attribute that might serve to prove compliance and
returning this attribute instead of Posture
information.
o Receiving Policy Attributes indicating the policies that
need to be met to be considered compliant. The collector
would obtain the Posture information from Component(s) on
the Endpoint and compare the information with the provided
(or referenced) security policy. The result would be sent
back to the Validator in Compliance Claim Attributes.
- If the Policy Attributes merely reference a compliance
policy, the collector may need to fetch or locate this
policy.
o Receiving Remediation Attributes containing instruction on
how to update the Component(s) on the Endpoint. This could
require the collector to interact with the User, Owner
and/or a remediation server.
o Monitoring the Posture of Component(s) on the Endpoint for
Posture changes that require notification to the Posture
Broker Client.
o Providing cryptographic verification of the Attributes
received from the Validator and offering cryptographic
protection to the Attributes returned.
The above list describes the model's view of the possible
responsibilities of the Posture Collector. Recall that this is
not a set of requirements for what each Posture Collector
implementation must support.
5.1.1.2 Posture Broker Client
The Posture Broker Client is a Component that is both a PA
Message multiplexer and a de-multiplexer. The Posture Broker
Client is responsible for de-multiplexing the Posture
information request from the NEA Server and distributing each
request to the corresponding Posture Collector(s). The model
also allows for the Posture information request to be pre-
provisioned on the NEA Client to improve performance by allowing
the NEA Client to report Posture without Request Attributes
being sent by the NEA Server.
The Posture Broker Client also multiplexes the responses from
the Posture Collector(s) and returns them to the NEA Server. The
Posture Broker Client constructs one or more PB Messages using
the PA Message(s) it obtains from the Posture Collector(s)
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involved in the Assessment. The quantity and ordering of
Posture Collector responses (PA Message(s)) multiplexed into the
PB response Message(s) can be determined by the Posture Broker
Client based on many factors including policy or characteristics
of the underlying network transport (e.g. MTU). A particular
NEA Client will have one Posture Broker Client.
The NEA model allocates the following responsibilities to the
Posture Broker Client Component:
o Maintaining a registry of known Posture Collectors and
allowing for Posture Collectors to dynamically
register/un-register.
o Multiplexing and de-multiplexing Attribute Messages
between the NEA Server and the relevant Posture
Collectors.
o Handling Posture Change Notifications from Posture
Collectors and triggering re-Assessment.
o Providing User notification about the global Posture
decision and other User Messages sent by the NEA Server.
5.1.1.3 Posture Transport Client
The Posture Transport Client is a component responsible for
establishing a reliable communication channel with the NEA
Server for the Message Dialog between the NEA Client and NEA
Server. There might be more than one Posture Transport Client on
a particular NEA Client. Certain Posture Transport Clients may
be configured with the address of the appropriate Posture
Transport Server to use for a particular network.
The NEA model allocates the following responsibilities to the
Posture Transport Client Component:
o Initiating and maintaining the communication channel to the
NEA Server, the Posture Transport Client hides the details
of the underlying carrier which could be a Layer 2 or Layer
3 protocol.
o Providing cryptographic protection for the Message Dialog
between the NEA Client and NEA Server.
5.1.2 NEA Server
The NEA Server will typically comprise of the following logical
components:
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o Posture Validator
o Posture Broker Server
o Posture Transport Server
The Posture Validator can be located on a separate server from
the Posture Broker Server requiring the Posture Broker Server to
deal with both local and remote Posture Validators.
5.1.2.1 Posture Validator
A Posture Validator is a Component that is responsible for
assessing the Posture Attributes from the corresponding Posture
Collector and determining the result of the Assessment. The
Posture Validator performs the Posture Assessment for one or
more Components and creates the result and if necessary the
remediation instructions. The Posture Validator can request a
set of primitive attributes or can pass compliance policies that
might be evaluated by the Posture Collector. The response from
the Posture Collector could be a set of Attributes or a set of
assertions in case of NEA Client based evaluation.
Each Posture Validator will be associated with an identifier
that enables it to be the specified as the destination in a PA
Message. The Posture Broker Server uses this identifier to
route Messages to this Validator. This identifier might be
dynamic (e.g. assigned by the Posture Broker Server upon
registration) or more static (e.g. provided during registration)
or a function of the Attribute Messages the validator desires to
receive (e.g. Message type subscription).
Posture Validators can be co-located on the NEA Server or can be
hosted on separate servers. A particular NEA Server is required
to handle several Posture Validators.
The NEA model allocates the following responsibilities to the
Posture Validator Component:
o Requesting Attributes from a Posture Collector. The
request may include:
- Request Attributes that indicate to the Posture
Collector to fetch and provide Posture Attributes from
various Component(s) on the NEA Client.
- Policy Attributes that indicate to the Posture
Collector the policies that need to met by various
Component(s) for them to be considered compliant.
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o Receiving Attributes from the Posture Collector. The
response from the Posture Collector may include:
- Posture Attributes collected from various
Component(s).
- Assertion Attributes that indicate the compliance
result from a prior Assessment.
- Compliance Claim Attributes in response to Policy
Attributes sent in the request.
o Assessing the Posture of the Component(s) based on the
various Attributes received from the Collector.
o Communicating the Posture Assessment Result to the Posture
Broker Server.
o Communicating the Posture Assessment Results to the Posture
Collector; this Attribute Message may include:
- Results Attribute that communicates the Posture
Assessment Result.
- Remediation Attributes that communicate the
Remediation Instructions to the Posture Collector.
o Monitoring out-of-band updates that trigger re-assessment
and require notifications to be sent to the Posture Broker
Server.
o Providing cryptographic protection for Attributes sent to
the Collector and offering cryptographic verification of
the Attributes received from the Collector.
5.1.2.2 Posture Broker Server
The Posture Broker Server is a Component that acts as a
multiplexer and a de-multiplexer for Attribute Messages. The
Posture Broker Client multiplexes the PA Messages, e.g. Messages
containing Request Attribute(s) from the relevant Posture
Validator(s) in one or more PB Messages and returns them to the
NEA Client. The Posture Broker Server de-multiplexes the PA
Messages received from the NEA Client and passes them to the
associated Posture Validators. The quantity and ordering of
Posture Collector responses (PA Message(s)) multiplexed into the
PB response Message(s) can be determined by the Posture Broker
Client based on many factors including policy or characteristics
of the underlying network transport (e.g. MTU).
The Posture Broker Server is also responsible for computing the
global Posture decision based on individual Posture Assessment
results from the various Posture Validators, this global Posture
decision is sent back to the NEA Client. A particular NEA Server
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will have one Posture Broker Server and this Posture Broker
Server will handle all the local and remote Posture Validators.
The NEA model allocates the following responsibilities to the
Posture Broker Server Component:
o Maintaining a registry of Posture Validators and allowing
for Posture Validators to register/un-register.
o Multiplexing and de-multiplexing Posture Messages between
the NEA Client and the relevant Posture Validators.
o Computing the global Posture decision based on Posture
Assessment results from the various Posture Validators.
5.1.2.3 Posture Transport Server
The Posture Transport Server is a Component responsible for
establishing a reliable communication channel with the NEA
Client for the Message Dialog between the NEA Client and NEA
Server. There might be more than one Posture Transport Servers
on a particular NEA Server. A particular Posture Transport
Server will typically handle requests from several Posture
Transport Clients and may require local configuration describing
how to reach the NEA Clients.
The NEA model allocates the following responsibilities to the
Posture Transport Server Component:
o Initiating and maintaining a communication channel with
potentially several NEA Clients.
o Providing cryptographic protection for the Message Dialog
between the NEA Client and NEA Server.
5.2 Protocols
The NEA Reference Model includes three layered protocols (PA, PB
and PT) that allow for the exchange of Attributes across the
different sets of Components on the network. While these protocols
are intended to be used together to fulfill a particular role in
the model, they may offer overlapping functionality. For example,
each protocol should be capable of protecting its information from
attack (see section 8.2 for more information).
5.2.1 Posture Attribute Protocol (PA)
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PA is a protocol that carries Attribute Messages between a
Posture Collector and its associated Posture Validator. The PA
protocol is required to handle several types of Attributes
including Posture Attributes, Request Attributes, Result
Attributes, Policy Attributes, Compliance Claim Attributes,
Assertion Attributes and Remediation Attributes. The PA protocol
also provides the requisite encoding and cryptographic
protection for the Posture Attributes.
5.2.2 Posture Broker Protocol (PB)
PB is a protocol that carries aggregate Attribute Messages
between the requested Posture Collectors on the NEA Client and
the corresponding Posture Validators on the NEA Server involved
in a particular Assessment. The PB protocol creates and manages
a Session allowing for Message Dialogs for every Assessment.
This PB Session is then used to bind multiple Posture Attribute
requests and responses from the different Posture Collectors and
Posture Validators involved in a particular Assessment. The PB
protocol may also carry the global Posture decision in the
Result Attribute from the Posture Broker Server to the Posture
Broker Client.
5.2.3 Posture Transport Protocol (PT)
PT is a transport protocol between the NEA Client and the NEA
Server responsible for carrying the Messages generated by the PB
protocol. The PT protocol(s) must be capable of transporting
Messages for Assessment during network connection request or
after network connectivity has been established. It is
conceivable that certain candidate PT protocols are capable of
transporting Messages both during network connection request and
after network connectivity has been established, but this isn't
a mandatory requirement for all candidate PT protocols. Should
the NEA WG select a PT protocol capable of operating only during
one time horizon, the WG should select an additional one so that
both horizons could be possible.
The PT protocol provides reliable Message delivery, mutual
authentication and cryptographic protection for the PB Messages.
5.3 Attributes
The PA protocol is responsible for the exchange of Attributes
between a Posture Collector and Posture Validator. Attributes are
effectively the reserved word "nouns" of the Posture Assessment.
The NEA Server is only able to ask for information that has a
corresponding Attribute, thus bounding what type of Posture can be
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obtained. The NEA WG will define a common (standard) set of
Attributes that are expected to be supported by all Posture
Collectors, but outside this set Posture Collectors may support
additional vendor-specific attributes.
As discussed in the Use Cases section below, depending on the
deployment scenario, different types of Attributes may be used.
The Attribute classes defined in this specification may be merged
when the NEA WG defines the name space and schema for each
Attribute class, but for now this specification recognizes their
distinct roles. This section summarizes the purpose of each class
of Attribute and how they are generated.
5.3.1 Attributes Normally Sent by NEA Client:
o Posture Attributes - Attributes and values sent to report
information about a particular aspect (based on semantic of
the Attribute) of the system. These Attributes are typically
sent in response to Request Attributes from the NEA Server.
For example a set of Posture Attributes might describe the
status of the firewall (e.g. If running, Vendor, Version).
The NEA Server would base its decision on comparing this type
of attribute against policy.
o Assertion Attributes - Attributes claiming recent prior
compliance to policy in hopes of avoiding a re-assessment.
These attributes might consist of NEA Server provided
attributes (state) describing a prior evaluation (e.g. opaque
to Endpoint, signed, time stamped items stating specific
results) or might consist of NEA Client identity information
used by the NEA Server to locate state about prior decisions
(e.g. system-bound cookie). These might be returned in lieu
of or addition to Posture Attributes.
o Compliance Claim Attributes - Attributes claiming compliance
with a particular policy provided by the NEA Server (in Policy
Attributes).
5.3.2 Attributes Normally Sent by NEA Server:
o Request Attributes - Attributes which define the specific
Posture information desired by the NEA Server. These
attributes might effectively form a template that the Posture
Collector fills in (subject to local policy restrictions) with
the specific value corresponding to each Attribute. The
resulting Attributes are typically Posture or Assertion
Attributes from the NEA Client.
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o Policy Attributes - Attributes including the NEA Server's
network access policies that the Endpoint must meet. These
Attributes are normally sent when the Endpoint is empowered to
merely provide the NEA Server with a compliance claim (in
Compliance Claim Attributes) without providing Posture
Attributes.
o Result Attributes - Attributes that contain the decisions of
the Posture Validators and/or Posture Broker Server. The
level of detail provided may vary from which individual
Attributes were compliant or not thru just the global
decision.
o Remediation Attributes - Attributes that describe to the NEA
Client and its User how to update the Endpoint to become
compliant with the NEA Server policies. These Attributes are
sent when the global decision was that the Endpoint is not
currently compliant. Remediation and Result Attributes may
both exist within an NEA Server Attribute Message.
6. Use Cases
This section discusses use cases with intent to describe and
collectively bound the NEA problem space under consideration.
The use cases provide a context and general rationale for the
defined requirements. In order to ease understanding of each
use case and how it maps to the reference model, each use case
will be accompanied by a simple example and a discussion of how
this example relates to the NEA protocols. It should be
emphasized that the provided examples are not intended to
indicate the only approach to addressing the use case but rather
are included to ease understanding of how the flows might occur
and require support from the NEA protocols.
We broadly classify the use cases into two categories each with
their own set of trigger events:
o Initial Assessment - evaluation of the Posture of an
Endpoint that has not recently been assessed and thus is
not in possession of any valid proof that it should be
considered compliant. This might be triggered by a request
to join a network, request to use a service or a desire to
understand the Posture of a system.
o Re-assessment - evaluation of the Posture of an endpoint
that has previously been assessed. This could occur for a
variety of reasons including the NEA Client or Server
recognizing an occurrence affecting the endpoint which
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might raise its risk level. This could be as simple as it
having been a long time since its last re-assessment.
6.1 Initial Assessment
An initial Assessment occurs when a NEA Client or Server event
occurs that causes the evaluation of the Posture of the Endpoint
for the first time. Endpoints that have been recently assessed
and the NEA Client or Server has maintained state (or proof)
that the Endpoint is compliant and therefore does not need to
have their Posture evaluated again do not qualify for this
category of use case.
Posture P.Broker Transport Transport P.Broker Posture
Collectors Client Client Server Server Validators
| | | | | |
| | client requests network access |
| | |---------->| | |
| | | |-------->|Posture reqs
| | | | |<----------|
| | | Posture Req | |
| | Pos Req |<----------|<--------| |
| Pos Req |<--------| | | |
|<--------| | | | |
|Pos Resp | | | | |
|-------->|Pos Resp | | | |
| |-------->| Posture Resp | |
| | |---------->|-------->| Pos Resp |
| | | | |---------->|
| | | | | Decisions |
| | | Posture Decision |<----------|
| | Decision|<----------|<--------| |
| Decision|<--------| | | |
|<--------| | | | |
| | | | | |
Figure 2: Illustration of NEA Initial Assessment Use case
6.1.1 Triggered by Network Connection Request
This use case focuses on Assessments performed at the time an
Endpoint attempts to join a network. This use case is particularly
interesting because it allows the NEA Server to evaluate the
Posture of an Endpoint before allowing it access to the network.
This approach could be used to help detect Endpoints with known
vulnerabilities and facilitate their repair before they are
admitted to the network and potentially exposed to such threats on
the network.
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6.1.1.1 Example
An IT employee returning from vacation boots his office desktop
computer which generates a request to join the wired enterprise
network. The network's security policy requires the system to
provide Posture information in order to determine whether the
desktop's security features are enabled and up to date. The
desktop sends its patch, firewall and anti-virus Posture
information. The network determines that the system is lacking
a recent security patch designed to fix a serious vulnerability
and places the system on a restricted access network. The
desktop follows the network provided remediation instructions to
download and install the necessary patch. Later, the desktop
requests again to join the network and this time is allowed on
the enterprise network after a full Assessment.
6.1.1.2 Possible flows and Protocol Usage
The following describes the Message flows through the NEA Reference
Model for the described example:
1. The IT employee's desktop computer connects to the network
through an access gateway in the wired enterprise network.
2. The Posture Broker Server on the NEA Server is notified of
the request to join the wired network.
3. Based upon compliance policy the Posture Broker Server
contacts the OS Patch, Firewall and Anti-Virus Posture
Validators to request the necessary Posture. Each Posture
Validator creates a PA Message containing the desired
Request Attributes for the desktop system.
4. The Posture Broker Server aggregates the Request Attributes
from the Posture Validators and sends them to the NEA Client
on the desktop using the Posture Transport Server.
5. The Posture Transport Client receives the Message from the
NEA Server and passes it to the Posture Broker Client for
Message delivery.
6. The Posture Broker Client de-multiplexes the PB Message and
delivers Request Attributes to the Firewall, OS Patch and
Anti-Virus Posture Collectors.
7. Each Posture Collector involved consults local privacy
policy to determine what information is allowed to be
disclosed and then returns the requested Posture Attributes
that are authorized in a PA Message to the Posture Broker
Client.
8. The Posture Broker Client aggregates these into a single PB
Message and sends it to the Posture Broker Server using the
Posture Transport Client to Server Session.
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9. The Posture Transport Server provides the PB Message to the
Posture Broker Server which de-multiplexes the Message and
sends the appropriate Posture Attributes to the
corresponding Posture Validator.
10. Each Posture Validator compares the contents of the Posture
Attribute Message it receives with the expected values
defined in its policy.
11. The Anti-Virus and Firewall Posture Validators return Result
Attributes stating it's compliant to the Posture Broker
Server, but the OS Patch Posture Validator returns non-
compliant and a PA Message with Result and Remediation
Attributes.
12. The Posture Broker Server sends the Result and Remediation
Attributes in a PB Message to the Posture Broker Client
13. The Posture Broker Client delivers the PA Message containing
Result and Remediation Attributes to the OS Patch Posture
Collector which interacts with the User to download and
install the needed patches.
14. Upon completion, the above steps 1-10 are repeated
(triggered by the NEA Client again requesting network
access).
15. This time the OS Patch Posture Validator (step 11) returns a
success status and the Posture Broker Server returns a
successful Result Attribute in a PB Message indicating a
global success.
16. The Posture Broker Client receives the successful Result
Attribute and the IT employee's desktop is now on the
network.
6.1.1.3 Impact on Requirements
The following are several different aspects of the use case example
that potentially need to be factored into the requirements.
o Posture Assessment before Endpoint allowed on network
o Endpoint sends Posture Attributes
o NEA Server sends Remediation Attributes
o NEA Client causes a re-assessment to join network after
remediation
6.1.2 Triggered by Request for Network Service
In this use-case, the Endpoint was allowed access to the network
without a NEA Posture validation. Now the Endpoint is
requesting use of a protected resource or service which results
in the need for an Assessment. There are a variety of possible
resources or network services that could be involved with this
use case (e.g. critical application server seeking tighter
security assurances of the accessing Endpoints).
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6.1.2.1 Example
The CEO of a small company working from home wishes to establish
a VPN connection into the office to read e-mail. The CEO is
already on the home IP-based network which did not perform an
initial Assessment. When the VPN service request reaches the
company's gateway, it wishes some assurance the CEO's system is
virus protected before allowing access to the company network.
The gateway's policies require the system be running anti-virus
that has up to date signatures, but does not wish to expose
details (potentially personal in nature) of what is running on
the system to the network. The gateway sends its specific
policy on allowable anti-virus products and versions to the
CEO's system and inquires as to whether it is compliant. The
CEO's system assesses the anti-virus software and determines it
meets the request policy, thus it sends a Message claiming it is
compliant. The gateway decides to trust the claim and allow the
system on the network.
6.1.2.2 Possible flows and Protocol Usage
The following describes the Message flows through the NEA Reference
Model for the remote User using a VPN to access the enterprise
network example:
1. CEO's computer initiates a remote access request to the VPN
gateway via his home network.
2. The VPN gateway triggers an authentication exchange with the
Endpoint. The protocol that carries this exchange does
double duty by also carrying the Posture Transport protocol.
3. The VPN gateway notifies the Posture Transport Server that a
new VPN session has been requested which triggers the
Posture Broker Server to initiate an NEA assessment.
4. The Posture Broker Server policy requires that Anti-Virus be
checked so it contacts the Anti-Virus Posture Validator.
5. Since in this case the Anti-Virus Posture Validator policy
trusts the NEA Client to perform the assessment it creates a
PA Message containing Policy Attributes including the most
recent Posture values describing the required Anti-Virus
policy that the CEO's computer must meet.
6. The Posture Broker Server assembles the PB protocol Message
containing the Policy Attributes, and forwards them to the
Posture Broker Client on the Endpoint over the PT protocol.
7. The gateway forwards the PB Message to the Posture Transport
Client in the NEA Client, which passes the Message to its
Posture Broker Client.
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8. The Posture Broker Client extracts the PA Message from the
PB Message and delivers it to the Anti-Virus Posture
Collector for processing.
9. The Anti-Virus Posture Collector finds Policy Attributes
(instead of the normal Request Attributes) so is empowered
to make a claim of compliance with respect to the included
(or referenced) policy.
10. The Anti-Virus Posture Collector obtains information about
the running Anti-Virus software and compares this
information with the provided Policy Attributes.
11. In this case, it determines the CEO's system is compliant
with the policy and creates a PA Message containing
Compliance Claim Attribute(s) describing the compliance.
The PA Message is returned to the Posture Broker Client.
12. The Posture Broker Client takes the Compliance Claims
Attributes from the Posture Collector, assembles a PB
protocol Message, and forwards it to NEA Server, via the
gateway, over the PT protocol.
13. The gateway in turn forwards the PT protocol Messages to the
Posture Transport Server on the NEA Server.
14. The Posture Broker Server de-multiplexes the Compliance
Claims Attributes and delivers them to the Anti-Virus
Posture Validator. The Posture Validator can return Result
Attributes indicating compliance status and, if required,
Remediation Attributes to the Posture Broker Server. In
this example, the Anti-Virus Posture Validator trusts the
claims that the CEO's system is compliant so creates a PA
Message containing a Result Attribute stating the system is
compliant and returns a successful Posture Assessment
Decision.
15. The Posture Broker Server creates a PB Message containing
the PA Message and includes a successful global compliance
decision, and returns it and specific Result Messages to the
NEA Client via the PB protocol.
16. The gateway is informed about the compliance status using
the PT protocol or other protocols, so that it can take the
appropriate enforcement action if required. The VPN
authentication process continues, in this case over the same
physical protocol as used for PT.
17. Upon successful VPN authentication appropriate enforcement
policies are applied. The gateway allows normal access to
an Endpoint that is in compliance.
6.1.2.3 Impact on Requirements
The following are several different aspects of the use case example
that potentially need to be factored into the requirements.
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o Posture Assessment after Endpoint on network, triggered by
service request
o NEA Server requests only anti-virus Posture
o Endpoint sends Compliance Claim Attributes rather than Posture
Attributes
o NEA Server decision based only on Compliance Attributes (no
Posture Attributes sent)
6.1.3 Triggered by Endpoint
This use case highlights that an Endpoint (possibly caused by a
User) may wish to trigger an Assessment of its Posture to
determine whether its security protective mechanisms are running
and up to date.
6.1.3.1 Example
A student goes to the terminal room to work on a project. The
terminal room contains shared systems owned by the school that
are on the network. These systems have been previously used by
other students so their security Posture is unknown. The
student wishes to check whether a system is currently in
compliance with the school's security policies prior to doing
work, so requests a Posture Assessment. The network performs an
Initial Assessment of the system and determines it's compliant
but the anti-virus protection is not in use. The student
receives an advisory response indicating the system's anti-virus
software is turned off but that otherwise it complies with the
school's policy. The student turns on the anti-virus software,
initiates a scan and upon completion decides to trust the system
with her work.
6.1.3.2 Possible flows and Protocol Usage
The following describes the Message flows through the NEA Reference
Model for the student using a terminal room shared system example:
1. Student triggers the Posture Broker Client on the computer
system in the terminal room to initiate a Posture
Assessment.
2. The Posture Broker Client establishes a Session with the
Posture Broker Server which causes an assessment to be
triggered.
3. The Posture Transport Client establishes the transport
channel to the Posture Transport Server causing a new
protocol context exchange to be initiated.
4. The Posture Broker Server detects the new Session and
consults policy to determine which Posture Validators to
involve in the assessment. The Posture Broker Server
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contacts several Posture Validators including the Anti-Virus
Posture Validator.
5. The Posture Validators involved create PA Messages
containing Request Attributes for information desired about
the terminal room computer based on the school's security
policy.
6. The Posture Broker Server assembles a PB Message including
each of the PA Messages from the Posture Validators.
7. The Posture Transport Server sends the PB Message to the
Posture Transport Client where it is passed on to the
Posture Broker Client.
8. The Posture Broker Client on the student's computer de-
multiplexes the PA Message and delivers them to the
corresponding Posture Collectors.
9. The Posture Collectors consult privacy policy to decide what
information to share with the Server. If allowable, the
collectors each return a PA Message containing Posture
Attributes to the Posture Broker Client.
10. The Posture Broker Client aggregates the returned PA
Messages into a PB Message and hands it to the Posture
Transport Client for transmission to the Posture Transport
Server.
11. The Posture Broker Server separates and distributes the
Posture Collector PA Messages to the associated Posture
Validators.
12. The Posture Validators determine whether the Posture
Attributes included in the PA Message are compliant with
their specific policies and returns a Posture Assessment
Decision to the Posture Broker Server. The anti-virus
Posture Validator returns a non-compliant decision because
the Anti-Virus software is not running. In case the User
wishes to activate the Anti-Virus software, the Validator
creates Remediation Attributes.
13. The Posture Broker Server determines the global compliance
decision based on each Validator's assessment decision and
sends Result Attributes containing the global decision and
the Anti-Virus's Remediation Attributes. In this case the
Result Attribute contains a compliant decision (despite the
single remediation attributes) because the Posture Broker
Server policy allowed for the Anti-Virus to not be running
as long as the system was properly patched and running a
Firewall (which were the case according to the other Posture
Validators). This information is included in a PB Message.
14. The Posture Transport Server sends the PB Message to the
Posture Transport Client which provides the Message to the
Posture Broker Client.
15. The Posture Broker Client on the student's computer examines
the Result Attribute's global decision and reports to the
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Student that the system was deemed to be compliant, but that
an advisory was included.
16. The Posture Broker Client provides the Remediation
Attributes to the Anti-Virus Posture Collector which
interacts with the User to explain how to turn on Anti-Virus
to improve the local protections.
17. The student turns on the Anti-Virus software and on
completion steps 1-10 are repeated.
18. This time the Anti-Virus Posture Validator returns a success
status and the Posture Broker Server returns a successful
Result Attribute in a PB Message indicating a global
success.
19. The Posture Broker Client receives the successful Result
Attribute on the student's computer and the student now uses
the computer for his/her assignment.
6.1.3.3 Impact on Requirements
The following are several different aspects of the use case example
that potentially need to be factored into the requirements.
o Voluntary, Endpoint requested Initial Assessment
o Successful (compliant) Result Attribute with an advisory
Remediation Attribute.
6.2 Posture Re-Assessment
Re-assessment(s) of Endpoints can happen anytime after being
admitted to the network after a successful initial NEA
Assessment. These may be event-based such as driven by Posture
changes detected by the NEA Client or changes detected by
network infrastructure such as detection of suspicious behavior
or network policy updates.
They may also be periodic (timer-driven) to re-assess the health
of the Endpoint.
Posture P.Broker Transport Transport P.Broker Posture
Collectors Client Client Server Server Validators
| | | | | |
| | initial assessment complete | |
| | |<--------->| |event triggered
| | | | |Posture request
| | | | |<----------|
| | | Posture Req | |
| | Pos Req |<----------|<--------| |
| Pos Req |<--------| | | |
|<--------| | | | |
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|Pos Resp | | | | |
|-------->|Pos Resp | | | |
| |-------->| Posture Resp | |
| | |---------->|-------->| Pos Resp |
| | | | |---------->|
| | | | | Decision |
| | | Posture Decision |<----------|
| | Decision|<----------|<--------| |
| Decision|<--------| | | |
|<--------| | | | |
| | | | | |
Figure 3: Illustration of NEA Posture Re-assessment Use case
6.2.1 Triggered by NEA Client
This use case allows for software on the Endpoint or a User to
determine that a re-assessment of the system is required. There
are a variety of reasons why such a re-assessment might be
beneficial including: changes in its previously reported Posture,
detection of potentially suspicious behavior or even to enable the
system to periodically poll the network to assess its condition
relative to the latest policies.
6.2.1.1 Example
The desktops within a company's HR department have a history of
poor security practices and eventual compromise. The HR
department administrator decides to deploy software on each
desktop to monitor the use of security protective mechanisms to
assure their use. One day, an HR person accidentally turns off
the desktop firewall. The monitoring process detects the lack
of a firewall and contacts the NEA Server to request a re-
Assessment of the firewall compliance. The NEA Server returns a
decision that the firewall must be re-activated to stay on the
network. The NEA Client explains the decision to the User and
how to re-activate the firewall. The HR person re-starts the
firewall and initiates a request to re-join the network.
6.2.1.2 Possible Flows & Protocol Usage
The following describes the Message flows through the NEA Reference
Model for the HR department example:
1. The Desktop Monitoring Software which typically might act as
a Posture Collector triggers the Posture Broker Client to
initiate a Posture Re-assessment. This PB Message contains a
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PA Message with the appropriate Posture Attribute indicating
the disabled desktop firewall.
2. The Posture Broker Client sends the PB Message to the
Posture Broker Server. The Posture Broker Client will create
a new session for the assessment.
3. The Posture Transport Client sends the PB Message to the
Posture Transport Server over the PT protocol.
4. The Posture Broker Server receives the PB Message and
forwards the Posture Attributes Message to the Firewall
Posture Validator responsible for handling Firewall related
Posture Attribute(s).
5. The Firewall Posture Validator processes the new value(s) of
the Posture Attribute(s) and determines that the Endpoint is
no longer compliant.
6. The Posture Validator generates a PA Message that includes a
Result Attribute with the Posture Assessment Decision set to
non-compliant and Remediation Attributes indicating how to
re-activate the firewall.
7. The Posture Validator communicates the PA Message with the
Posture Assessment Result to the Posture Broker Server and
instructs it to respond back to the NEA Client.
8. The Posture Broker Server generates a PB Message with the
Global Posture Assessment Decision and PA Message from the
Firewall Posture Validator.
9. The Posture Transport Server transports the PB Message to
the Posture Transport Client where it is passed to the
Posture Broker Client.
10. The Posture Broker Client processes the Result Attribute
received from the NEA Server and displays non-compliance
Messages to the end User.
11. The Posture Broker Client forwards the PA Message to the
Firewall Posture Collector; the Posture Collector guides the end
User with instructions to be compliant which includes enabling
the Desktop Firewall.
12. The end User will be prompted to initiate a Re-assessment after
completing the Remediation.
13. Upon completion of the remediation, the NEA Client re-initiates
a request for re-assessment and steps 1-4 are repeated. This
time the Firewall Posture Validator determines the Endpoint is
compliant and returns a successful Posture Assessment Decision.
14. The successful Posture Broker Server generates a PB Message with
a Global Posture Assessment of compliant and returns this to the
NEA Client.
6.2.1.3 Impact on Requirements
The following are several different aspects of the use case example
that potentially need to be factored into the requirements.
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o Voluntary, Endpoint (software) initiated Posture evaluation
request
o NEA Server requests specific firewall-oriented Posture
Attributes
o NEA Client (firewall Posture Collector) interact with User to
fix problem
6.2.2 Triggered by NEA Server
In many cases, especially for re-assessment, the NEA Server may
initiate specific or complete re-assessment of one or more Endpoints
triggered by:
o Time (periodic)
o Event occurrence
6.2.2.1 Example
An enterprise requires employees on the network to always stay
up to date with security critical operating system patches. A
marketing employee joins the network and performs an Initial
Assessment. The Assessment determines the employee's laptop is
compliant. Several hours later, a major operating system vendor
releases a set of patches preventing a serious vulnerability
that is being exploited on the Internet.
The enterprise administrators make available the patches and
change the network policy to require it to be installed by 5PM.
This policy change causes the NEA Server to request a re-
assessment to determine what Endpoints are impacted and lacking
the patches. The marketing employee's laptop is re-assessed and
determined to need the patches. A remediation advisory is sent
and presented to the employee how to obtain the patch and that
it must be installed by 5PM. The marketing employee immediately
downloads and installs the patch and obtains an assertion that
the patches are now installed.
At 5PM the enterprise performs another re-assessment of all
impacted Endpoints to determine if they are now in compliance.
The marketing employee's laptop is re-assessed and presents the
assertion that it has the patches installed and thus is allowed
to remain on the network.
6.2.2.2 Possible Flows and Protocol Usage
The following describes the Message flows through the NEA Reference
Model for the above example:
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1. Marketing employee joins network and completes an initial
Assessment resulting in a compliant decision.
2. The Enterprise Administrator configures an OS Patch policy
for indicating that recent patches are required on all
Endpoints by 5PM to prevent serious vulnerabilities.
3. The NEA Server's OS Patch Posture Validator become aware of
this policy change and creates a PA Message containing a
Request Attributes for information about OS patches in use
and triggers the Posture Broker Server to initiate a Posture
Re-Assessment of all Endpoints connected to the network.
4. The Posture Broker creates a PB Message that includes the PA
Message that contains the set of Request Attribute(s) that
are related to OS patch versions.
5. The Posture Broker Server establishes a session with each
available NEA Client. The rest of the flow focuses on the
exchanges between the NEA Server and one NEA Client; the NEA
Server will engage in such a Message Dialog with each
available NEA Client.
6. The Posture Broker Server sends the PB Message to the
Posture Broker Client.
7. The Posture Transport Server carries the PB Message to the
Posture Transport Client over the PT protocol.
8. The Posture Broker Client receives the PB Message and
forwards the PA Message to the appropriate Posture Collector
responsible for handling OS Patch Request Attribute(s).
9. The OS Patch Posture Collector determines the OS patches
present on the Endpoint and if authorized by its disclosure
policy accumulates the value(s) for each Posture Attribute
requested by the Posture Validator.
10. The OS Patch Posture Collector constructs a PA Message and
includes the authorized Posture Attributes accumulated about
the OS patches.
11. The Posture Collector instructs the Posture Broker Client to
respond back to the NEA Server with the PA Message.
12. The Posture Broker Client sends a PB Message that includes
the OS Patch PA Message.
13. The Posture Transport Client transports the PB Message to
the Posture Transport Server where it is passed to the
Posture Broker Server.
14. The Posture Broker Server receives the PB Message and delivers
the PA Message to the OS Patch Posture Validator.
15. The OS Patch Posture Validator extracts the Posture
Attribute(s) from the PA Message and uses the values to
determine whether the Endpoint is compliant with the new
policy. The Posture Validator determines that the Endpoint
is not compliant since it does not have the new OS patches
installed.
16. The Posture Validator generates a PA Message that includes a
Result Attribute with the Posture Assessment Decision set to
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non-compliant and appropriate Remediation Attributes to
enable the Endpoint to download the required OS patches.
17. The Posture Validator communicates the Posture Assessment
Result to the Posture Broker Server and instructs the
Posture Broker to respond back to the NEA Client with the
Posture Attribute Message.
18. The Posture Broker Server generates a Global Posture
Assessment Decision and sends a PB Message with the Result
Attribute and Posture Attribute Message.
19. The Posture Transport Server transports the PB Message to
the Posture Transport Client where it is passed to the
Posture Broker Client.
20. The Posture Broker Client processes the Result Attribute
received from the NEA Server and displays the non-compliance
Messages to the User.
21. The Posture Broker Client forwards the PA Message to the OS
Patch Posture Collector; the Posture Collector guides the User
with instructions on how to become compliant that includes
downloading the appropriate OS patches to prevent the
vulnerability.
22. The marketing employee installs the required patches and how is
in compliance.
23. The NEA Client triggers a re-assessment of the OS Patches which
causes a repeat of many of the steps above. This time step 15
determines the marketing employee's laptop is compliant and
returns re-usable (signed and dated) Assertion Attributes in the
PA Message instead of Remediation Attributes as before.
24. This time when the OS Patch Posture Collector receives the PA
Message that contains Assertion Attributes which is caches for
future use.
25. Later at 5PM, the NEA Server triggers a Re-assessment to
determine compliance to the patch advisory. When the OS Patch
Posture Collector receives the Request Attributes (like in step
9-10 above) it will return Assertion Attributes (instead of
Posture Attributes) to indicate that the patches have been
installed instead of engaging in the entire assessment process.
26. When the OS Patch Posture Validator receives the PA Message
containing the Assertion Attributes it is able to determine that
they are authentic and returns a Posture Assessment Decision of
compliant thus allowing the laptop to remain on the network.
6.2.2.3 Impact on Requirements
The following are several different aspects of the use case example
that potentially need to be factored into the requirements.
o Server initiated re-assessment required due to urgent patch
availability
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o NEA Client submits Assertion Attributes instead of Posture
that patch is installed
o NEA Server capable of recognizing Assertion Attributes are
sufficient instead of Posture Attributes
7. Requirements
This section describes the requirements that will be used by the
NEA WG to assess and compare candidate protocols for PA, PB and
PT. These requirements frequently express features that a
candidate protocol must be capable of offering so that a
Deployer can decide to make use of that feature. This section
does not state requirements about what features of each protocol
must be used during a deployment.
For example, a requirement may exist for cryptographic security
protections to be available from each protocol but this does not
require that a Deployer make use of all or even any of them
should they deem their environment to offer other protections
which are sufficient.
7.1 Common Protocol Requirements
The following are the common requirements that apply to the PA,
PB and PT protocols in NEA conceptual architecture:
C-1 NEA protocols MUST be capable of performing a multiple
Message Dialog between the NEA Client and NEA Server.
This allows for Assessment models that require more than
one round trip to complete the Assessment. This also
allows for updates to already reported Posture
information. These updates allow for detection of recent
changes in the Endpoint state (e.g. possibly due to a
remediation).
C-2 NEA protocols MUST allow Posture Assessment to occur
before or after the Endpoint has established network
connectivity. The support for both time periods will
facilitate multiple deployment models including those that
leverage the network access technology to restrict access
based on Posture. Should the WG select a protocol used
only during one time period, this requirement would cause
the selection of an additional protocol with coverage of
the other time period.
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C-3 NEA protocols MUST provide a way for both the NEA Client
and the NEA Server to initiate a Posture re-assessment
request as needed.
C-4 NEA protocols MUST provide protection against active and
passive attacks by intermediaries including protection to
prevent replay based attacks.
C-5 The PA and PB protocols defined by NEA MUST be agnostic of
the transport i.e. PT protocol. For example, the PB
protocol must provide a transport independent interface
allowing the PA protocol to operate without change across
a variety of network protocol environments (e.g.
EAP/802.1X, PANA, and IKE/IPsec).
C-6 The selection process for NEA protocols MUST evaluate and
prefer the reuse of existing open standards that meet the
requirements before defining new ones. The goal of NEA is
not to create additional alternative protocols where
acceptable solutions already exist.
C-7 NEA protocols MUST be highly scalable; the protocols MUST
support many Posture Collectors on a large number of NEA
Clients to be assessed by numerous Posture Validators
residing on multiple NEA Servers.
C-8 The protocols MUST support efficient transport of a large
number of Attributes Messages between the NEA Client and
the NEA Server.
C-9 The protocols MUST support deployments that have large
numbers of compliance policies.
C-10 The protocols MUST allow for Assessment modes that can
reduce the amount information to be exchanged between the
NEA Client and Server to complete an assessment.
7.2 Posture Attribute (PA) Protocol Requirements
The Posture Attribute (PA) protocol defines the transport and data
model to carry Posture and validation information between a
particular Posture Collector associated with the NEA Client and a
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Posture Validator associated with an NEA Server. The PA protocol
carries collections of standard attributes and vendor-specific
attributes. The PA protocol itself is carried inside the PB
protocol.
The following requirements define the desired properties that form
the basis for comparison and evaluation of candidate PA protocols.
These requirements do not mandate the use of these properties, but
merely that the candidate protocols are capable of offering the
property if it should be needed.
PA-1 The PA protocol MUST support transport of the required
(standard) Attributes defined in the data model.
PA-2 The PA protocol MUST support the transport of vendor-specific
Attributes.
PA-3 The PA protocol MUST enable a Posture Validator to request
Posture, Compliance Claims, and Assertion Attributes about
particular Components on the NEA Client system from its peer
Posture Collector.
PA-4 The PA protocol MUST enable a Posture Validator to request
Posture, Compliance Claims, and Assertion Attributes from its
peer Posture Collector on more than one occasion using an
existing or new Session. This enables the Posture Validator
to reassess the Posture of a particular Component or to
request information about additional Component.
PA-5 The PA protocol MUST be capable of returning Results and
Remediation Attributes from the Posture Validator. This
enables the Posture Collector to learn the specific reason
for a failed Assessment and to aid in remediation and
notification of the system owner.
PA-6 The PA protocol SHOULD support expression of standard
Attributes to describe remediation state of Components, for
example, last update time or remediation server used. These
Attributes are used after remediation so that a Posture
Validator can synchronize with a Posture Collector and
continue remediation.
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PA-7 The PA protocol MUST support authentication, integrity, and
confidentiality of Attributes, results, and remediation
instructions sent between a Posture Collector and Posture
Validator. This enables end-to-end security across an NEA
deployment that might involve traversal of several systems.
PA-8 The PA protocol MUST be capable of carrying attributes that
contain binary data including encrypted content.
PA-9 String Attributes MUST support being encoded with an
encoding standard that supports internationalization.
7.3 Posture Broker (PB) Protocol Requirements
The PB protocol supports multiplexing of Posture Attribute Messages
(based on PA protocol) from multiple Posture Collectors associated
with a NEA Client and transmitting them to an NEA Server, where
they can be de-multiplexed to potentially multiple corresponding
Posture Validators.
The PB protocol carries the global decision made by the Posture
Broker Server, taking into account the results of the Posture
Validators involved in the Assessment, to the Posture Broker
Client. The PB protocol also aggregates and transports advisories
and notifications such as remediation instructions and patch
references from one or more Posture Validators.
The requirements for the PB protocol are:
PB-1 The PB protocol MUST be capable of carrying the Result
Attributes and, if appropriate, the Remediation Attributes
from the Posture Broker Server to the Posture Broker Client.
PB-2 The PB protocol MUST carry identifiers that are used by the
Posture Brokers to route (deliver) Messages between peer
Posture Collectors and Posture Validators. Such Message
routing should facilitate dynamic (de)registration of Posture
Collectors and Validators to the NEA service. For example, a
dynamically registered Anti-Virus Posture Validator should be
able to subscribe to receive Messages from its respective
Anti-Virus Posture Collector on NEA Clients.
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PB-3 The PB protocol MUST support creation and management of a
Session that can carry a Message Dialog between one or more
Posture Collectors and Posture Validators. This allows each
party to send multiple Messages before the dialog is
complete.
PB-4 The PB protocol SHOULD support authentication, integrity and
confidentiality protection for the Attribute Messages it
carries between an NEA Client and Server. This provides
security protection for a Message Dialog of the groupings of
Attribute Messages exchanged between the NEA Client and
Server. Such protection is orthogonal to PA protections
(which are end to end) and allow for simpler Posture
Collector and Validators be implemented, and for
consolidation of cryptographic operations possibly improving
scalability and manageability.
PB-5 The PB protocol MUST support grouping of Attribute Messages
to optimize transport of Messages and minimize round trips.
7.4 Posture Transport (PT) Protocol Requirements
The Posture Transport (PT) protocol carries PB protocol Messages
between the Posture Transport Client and the Posture Transport
Server. PT is responsible for providing a protected transport for
the PB protocol. The PT protocol may itself be transported by one
or more concatenated sessions using lower layer protocols, such as
802.1X, RADIUS, TLS, or IKE.
This section defines the requirements that candidate PT protocols
must be capable of supporting.
PT-1 The PT protocol SHOULD incur low overhead to accommodate us
on low bandwidth links
PT-2 The PT protocol SHOULD be capable of supporting a half-duplex
communication environment.
PT-3 The PT protocol MUST NOT attempt to interpret the contents of
PB Messages being transported, i.e., the data it is carrying
must be opaque to it.
PT-4 The PT protocol MUST be capable of protecting the integrity
and confidentiality of the PB Messages between the Posture
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Transport Client and the Posture Transport Server. This
includes protection against replay and reflection.
PT-5 The PT protocol MUST provide reliable delivery for the PB
protocol. This includes the ability to perform fragmentation,
reassembly, and detect duplicates and reorder to provide in-
sequence delivery, as required.
PT-6 The PT protocol MUST be capable of supporting mutual
authentication between the Posture Transport Client and the
Posture Transport Server. This MAY occur by leveraging by-
products (e.g., keys) supplied by the PB protocol
authentication.
PT-7 The PT protocol MUST support establishing a restricted
Session between the Posture Transport client and the Posture
Transport server prior to the NEA Client being granted
unrestricted network access.
PT-8 The PT protocol MUST allow either the Posture Transport
Client or the Posture Transport Server to initiate a
restricted session for use by NEA when both parties have
necessary network addresses established.
8. Security Considerations
This document defines the functional requirements for the PA, PB
and PT protocols used for Network Endpoint Assessment. As such, it
does not define a specific protocol stack or set of technologies,
so this section will highlight security issues that may apply to
NEA in general or to particular aspects of the reference model's
components.
8.1 Trust
Network Endpoint Assessment involves assessing the Posture of
Endpoints entering or already on the network against compliance
policies to assure they are adequately protected. Therefore, there
is an implied distrusting of Endpoints until there is reason to
believe (based on Posture information) that they are well protected
and can be trusted to not infect/attack other Endpoints. On the
network provider side, the NEA Client normally is expected to trust
the network infrastructure systems not to misuse any disclosed
Posture information (see section 9) and any remediation
instructions necessary to join the network. The NEA Client
normally needs to trust that the NEA Server will only request
information required to determine whether the Endpoint is safe to
access the network assets.
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In between the NEA Client and Server exists a network that is not
assumed to be trustworthy. Therefore, little about the network is
implicitly trusted beyond its willingness and ability to transport
the exchanged Messages in a timely manner. The amount of trust
given to each of these parties is deployment specific. The NEA
Reference Model intends to provide security mechanisms to reduce
the amount of trust that must be assumed by a Deployer. The
following sections will discuss each area in more detail.
8.1.1 Endpoint Components
For NEA to properly operate, the Endpoint needs to be trusted to
accurately represent the requested security Posture of the Endpoint
to the NEA Server. By NEA WG charter, the NEA Reference Model does
not explicitly specify how to detect or prevent lying endpoints
that intentionally misrepresent their Posture. Similarly, the
detection of malware (e.g. root kits) that are able to trick the
Posture Collectors into returning incorrect information is the
subject for research and standardization outside the IETF (e.g.
Trusted Computing Group) and is not specifically addressed by the
model. However, if such mechanisms do come into existence, the NEA
Reference Model should be able to accommodate these technologies by
allowing them to communicate over PA to Posture Validators or work
orthogonally to protect the NEA Components from attack and assure
the ability of Posture Collectors to view the actual Posture.
Besides having to trust the integrity of the NEA Components and
their ability to properly collect and report Posture Attributes
about the Endpoint, we try to limit other assumed trust. Most of
the usage models for NEA expect the Posture information to be sent
to the NEA Server for evaluation and decision making. However, one
approach assumes more trust in the Endpoint. This approach allows
for the NEA Client to receive compliance policies in Policy
Attributes and perform the comparison of the current Posture to the
policies and make a claim of compliance in Compliance Claim
Attributes to the NEA Server instead of providing the Posture
Attributes themselves. In this case, the NEA Server must trust the
Endpoint's policy storage, comparison and reporting mechanisms to
not falsify the results of the Posture evaluation.
Generally the Endpoint should not trust network communications
(e.g. inbound connection requests) unless it has been specifically
authorized by the User or Owner defined policy. The NEA Reference
Model assumes all the NEA Client components are local to the
Endpoint and communicate over local API or program calls.
Unsolicited communications originating from the network should be
inspected by normal security protective mechanisms (e.g. firewalls,
security protocols, IDS/IPS, etc). Communications associated with
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the NEA Assessment or re-assessment requires some level of trust
particularly when initiated by the NEA Server (re-assessment). The
degree of trust can be limited by use of strong security
protections on the Messages as dictated by the network Deployer and
the Endpoint User/Owner policy.
8.1.2 Network Communications
Between the NEA Client and Server there may exist a variety of
types of devices to facilitate the communication path. Some of the
devices may serve as intermediaries (e.g. simple L2 switches) so
may have the opportunity to observe and change the Message Dialogs.
The intermediary devices may fall into a few major categories which
impact our degree of trust in their operation. First, some
intermediary devices may act as Message forwarders or carriers for
PT (e.g. L2 switches, L3 routers, or alike). For these devices we
trust them not to drop the Messages or actively DOS the NEA
deployment.
Second, some intermediary devices may be part of the access control
layer of the network and as such we trust them to enforce policies
including remediation isolation and access controls given to them
by the NEA Server. These devices may also fill other types of
roles described in this section.
Third, some devices may act as a termination point or proxy for the
PT carrier protocol. Frequently, it's expected that the carrier
protocol for PT will terminate on the NEA Client and Server so will
be co-resident with the PT endpoints. If this expectation is not
present in a deployment, we must trust the termination device to
accurately proxy the PT Messages without alteration into the next
carrier protocol (e.g. if inner EAP method Messages are
transitioned from an EAP [EAP] tunnel to a RADIUS [RADIUS]
session).
Fourth, many networks include infrastructure such as IDS/IPS
devices which monitor and take corrective action when suspicious
behavior is observed on the network. These devices may have a
relationship with the NEA Server which is not within scope for this
specification. Devices trusted by the NEA Server to provide
security information that might affect the NEA Server's decisions
are trusted to operate properly and not cause the NEA Server to
make incorrect decisions.
Finally, other types of intermediary devices may exist on the
network between the NEA Client and Server which are present to
service other network functions beside NEA. These devices might be
capable of passively eavesdropping on the network archiving
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information for future purposes (e.g. replay or privacy invasion)
or more actively attacking the NEA protocols. Because these
devices do not play a role in facilitating NEA, it's essential that
NEA Deployers not be forced to trust them for NEA to reliably
operate. Therefore, it is required that NEA protocols offer
security protections to assure these devices can't steal, alter,
spoof or otherwise damage the reliability of the Message Dialogs.
8.1.3 NEA Server Components
The NEA Server components including systems providing (remote)
Posture Validation are generally trusted to enforce the specified
Assessment policies and are protected from compromise. It's
essential that NEA Server deployments properly safeguard these
systems from a variety of attacks from the network and Endpoints to
assure their proper operation.
While we need to trust the NEA Server operation to some degree,
rigorous security architecture, analysis, monitoring and review
should assure their network footprint and internal workings are
protected from attack. The network footprint would include
communications over the network which might be subject to attack
such as policy provisioning from the policy authoring systems and
general security and system management protocols. Some examples of
internal workings include protections from malware attacking the
intra-NEA Component communications, Component inner workings or
policy stores particularly those that would change the resulting
decisions or enforcements. The NEA Server needs to trust the
underlying carrier protocols to properly behave and safeguard the
exchanged Messages with the Endpoint. The NEA Reference Model does
not attempt to address integrity protection of the operating system
or other software supporting the NEA Server.
One interesting example combines aspects of both areas, where each
of the NEA Server Components physically reside in different
systems. This might occur when a Posture Validator (or a remote
backend server used by a local Posture Validator) exists on another
system from the Posture Broker Server. Similarly, the Posture
Broker Server might exist on a separate system from the Posture
Transport Server. When there is a physical separation, the
communications between the NEA Server components must ensure that
the PB Session and PA Message Dialogs are resistant to active and
passive attacks, in particular, guarded against eavesdropping,
forgery and replay.
8.2 Protection Mechanisms at Multiple Layers
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Inherent in the requirements is a desire for NEA candidate
protocols throughout the Reference Model to be capable of providing
strong security mechanisms as dictated by the particular
deployment. In some cases, these mechanisms may appear to provide
overlapping or redundant protections. These apparent overlaps may
be used in combination to offer a defense in depth approach to
security. However because of the layering of the protocols each
set of protections offers slightly different benefits and levels of
granularity.
For example, a Deployer may wish to encrypt traffic at the PT layer
to protect against some forms of traffic analysis or interception
by an eavesdropper. Additionally, the Deployer may also selectively
encrypt some set of Posture Attributes to achieve end to end
confidentiality to its peer Posture Validator. In particular, this
might be desired when the Posture Validator is not co-located with
the PT Server so the information will traverse additional network
segments after the PT protections have been enforced.
Different use cases and environments for the NEA technologies will
likely influence the selection of the strength and security
mechanisms employed during an Assessment. The goal of the NEA
requirements is to encourage the selection of technologies and
protocols that are capable of enforcing the necessary protections
for a wide variety of types of Assessment.
8.3 Relevant Classes of Attack
A variety of attacks are possible against the NEA protocols and
Assessment technologies. This section does not include a full
security analysis, but wishes to highlight a few attacks that
influenced the requirement definition and should be considered by
Deployers selecting use of protective mechanisms within the NEA
Reference Model.
As discussed, there are a variety of protective mechanisms included
in the requirements for candidate NEA protocols. Different use
cases and environments may cause Deployers to decide not to use
some of these mechanisms; however this should be done with an
understanding that the deployment may become vulnerable to some
classes of attack. As always a balance of risk vs. performance,
usability, manageability and other factors should be taken into
account.
The following types of attacks are applicable to network protocols
defined in the Reference Model and thus should be considered by
Deployers.
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8.3.1 Man-in-the-Middle (MITM)
MITM attacks against a network protocol exist when a third party
can insert itself between two communicating entities without
detection and gain benefit from involvement in their Message
Dialog. For example, a malware infested system might wish to join
the network replaying Posture observed from a clean Endpoint
entering the network. This might occur by the system inserting
itself into and actively proxying an Assessment Message Dialog. The
impact of the damage caused by the MITM can be limited or prevented
by selection of appropriate protocol protective mechanisms.
For example, the requirement for PT to be capable of supporting
mutual authentication prior to any Endpoint Assessment Message
Dialogs prevents the attacker from inserting themselves as an
active participant (proxy) within the communications without
detection (assuming attacker lacks credentials convincing either
party it is legitimate). Re-usable credentials should not be
exposed on the network to assure the MITM doesn't have a way to
impersonate either party. The PT requirement for confidentiality
protected (encrypted) communications linked to the above
authentication prevent a passive MITM from eavesdropping by
observing the Message Dialog and keeping a record of the conformant
Posture values for future use. The PT requirement for replay
prevention stops the passive MITM from later establishing a new
Session (or hijacking an existing Session) and replaying previously
observed Message Dialogs.
8.3.2 Message Modification
Without Message integrity protection, an attacker capable of
interception of a Message might be capable of modifying its
contents and causing an incorrect decision to be made. For
example, the attacker might change the Posture Attributes to always
reflect incorrect values and thus prevent a compliant system from
joining the network. Unless the NEA Server could detect this
change, the attacker could prevent admission to large numbers of
clean systems. Conversely, the attacker could allow malware
infested machine to be admitted by changing the sent Posture
Attributes to reflect compliant values, thus hiding the malware
from the Posture Validator.
In order to protect against such attacks, the PT includes a
requirement for strong integrity protection (e.g. including a
protected hash like an HMAC [HMAC] of the Message) so this change
would be detected. PA includes a similar requirement to enable end
to end integrity protection of the Attributes extending the
protection all the way to the Posture Validator even if it existed
on another system behind the NEA Server.
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It is important that integrity protection schemes leverage fresh
secret information (not known by the attacker) that is bound to the
authenticated Session such as an HMAC using a derived fresh secret
associated with the Session. Inclusion of freshness information
allows the parties to protect against some forms of Message replay
attacks using secret information from prior Sessions.
8.3.3 Message Replay or Attribute Theft
An attacker might listen to the network recording Message Dialogs
or Attributes from a compliant Endpoint for later re-use to the
same NEA Server or just to build an inventory of software running
on other systems watching for known vulnerabilities. The NEA
Server needs to be capable of detecting the replay of Posture
and/or the model must assure that the eavesdropper can not obtain
the information in the first place.
The cryptographic protection from disclosure of the PT, PB or PA
Messages prevents the passive listener from observing the exchanged
Messages and thus prevents theft of the information for future use.
However an active attacker might be able to replay the encrypted
Message if there is no strong link to the originating party or
session. By linking the encrypted Message Dialog to the
authentication event and leveraging per-transaction freshness and
keying exchanges, this prevents a replay of the encrypted
transaction.
8.3.4 Other Types of Attack
This section doesn't claim to present an exhaustive list of attacks
against the NEA Reference Model. Several types of attack will
become easier to understand and analyze once the NEA WG has created
specifications describing the specific selected technologies and
protocols to be used within NEA. One such area is Denial of
Service (DoS). At this point in time it's not practical to try to
define the all of the potential exposures present within the NEA
protocols, so such an analysis should be included in the Security
Considerations sections of the selected NEA protocols.
However, it's important that the NEA Server be resilient to DoS
attacks as an outage might affect large numbers of Endpoints
wishing to join or remain on the network. The NEA Reference Model
expects that the underlying carrier protocols would have some
amount of DoS resilience and that the NEA protocols would need to
build upon that base with their own protections. To help narrow
the window of attack by unauthenticated parties, it is envisioned
that NEA Servers would employ carrier protocols that enable an
early authentication of the requesting Endpoint as one technique
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for filtering out attacks. The PT protocol also requires support
of a mutual authentication that can be used in addition to (or in
lieu of) the carrier authentication to limit the window of
unauthenticated attack against the Posture assessment.
Attacks occurring after the authentication would at least come from
sources possessing valid credentials and could potentially be held
accountable. Similarly, NEA protocols should offer strong replay
protection to prevent DoS based attacks based on replayed Sessions
and Messages. Posture assessment should be strongly linked with
the carrier and/or Posture Transport authentications that occurred
to assure the Posture came from the authenticated party.
Cryptographic mechanisms and other potentially resource intensive
operations should be used sparingly until the validity of the
request can be established. This and other resource/protocol based
attacks can be evaluated once the NEA technologies and their
cryptographic use have been selected.
9. Privacy Considerations
While there are a number of beneficial uses of the NEA
technology for organizations that own and operate networks
offering services to similarly owned Endpoints, these same
technologies might enhance the potential for abuse and invasion
of personal privacy if misused. This section will discuss a few
of the potential privacy concerns raised by the deployment of
this technology and offer some guidance to implementers.
The NEA technology enables greater visibility into the
configuration of an Endpoint from the network. Such
transparency enables the network to take into consideration the
strength of the Endpoint's security mechanisms when making
access control decisions to network resources. However this
transparency could also be used to enforce restrictive policies
to the detriment of the User by limiting their choice of
software or prying into past or present uses of the Endpoint.
The scope of the NEA WG was limited to specify protocols
targeting the use cases where the Endpoints and network are
owned by the same party or a clear expectation of
disclosure/compliance has been established with the network
owner. This is a familiar model for governments, institutions
and a wide variety of enterprises that provide Endpoints to
their employees to perform their jobs. In many of these
situations, the Endpoint is purchased and owned by the
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enterprise and they often reserve the right to audit and
possibly dictate the allowable uses of the device. The NEA
technologies allow them to automate the inspection of the
contents of an Endpoint and this information may be linked to
the access control mechanisms on the network to limit their use
should they not meet minimal compliance levels.
In these environments, the level of personal privacy the
employee enjoys may be significantly reduced subject to local
laws and customs. However, in situations where the Endpoint is
owned by the User or where local laws protect the rights of the
User even when using Endpoints owned by another party, it's
critical that the NEA implementation enable the User to control
what Endpoint information is shared with the network. Such
controls imposed by the User might prevent or limit their
ability to access certain networks or protected resources, but
this must be a User choice.
9.1 Implementer Considerations
The NEA WG is not defining NEA Client policy content standards
nor defining requirements on aspects of an implementation
outside of the network protocols, however the following guidance
is provided to encourage privacy friendly implementations for
broader use than just the enterprise oriented setting described
above.
NEA Client implementations are encouraged to offer an opt-in
policy to Users prior to sharing their Endpoint's Posture
information. The opt-in mechanism should be on a per-User, per-
NEA Server basis so each User can control which networks can
access any Posture information on their system. For those
networks that are allowed to assess the Endpoint, the User
should be able to specify granular restrictions on what
particular types and specific Attributes Posture Collectors are
allowed to disclose.
Requests for Attributes that are explicitly not allowed to be
shared should result in a User notification and/or log record so
the User can assess whether the service is doing something
undesirable or whether the User is willing to share this
additional information in order to gain access. Some products
might consider policy-driven support for prompting the User for
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authorization with a specific description of the Posture
information being requested prior to sending it to the NEA
Server.
It's envisioned that the Owner of the Endpoint is able to
specify disclosure policies that may override or influence the
User's policies of the Attributes visible to the network. If
the Owner disclosure policy allows for broader Posture
availability than the User policy, the implementation should
provide a feedback mechanism to the User so they understand the
situation and can choose to whether to use the Endpoint in those
circumstances.
In such a system, it is important that the User's policy
authoring interface be easy to understand and clearly
articulates the current disclosure policy of the system
including any influences from the Owner policy. Users should be
able to understand what Posture is available to the network and
the general impact of this information being known. In order to
minimize the list of restrictions enumerated, use of a
conservative default disclosure policy such as "that which is
not explicitly authorized for disclosure is not allowed" might
make sense to avoid unintentional leakage of information.
NEA Server implementations should provide newly subscribing
Endpoints with a disclosure statement that clearly states:
o What information is required,
o How this information will be used/protected,
o What local privacy policies are applicable.
This information will empower subscribing Users to decide
whether the disclosure of this information is acceptable
considering local laws and customs.
9.2 Minimizing Attribute Disclosure
One important issue in the design of the NEA Reference Model and
protocols is enabling Endpoints to disclose minimal information
required to establish compliance with network policies. There
are several models that could be considered as to how the
disclosed Attribute set is established. Each model has benefits
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and issues and these descriptions are provided to seed
discussion as to whether each is feasible and whether a
preferred approach will emerge potentially impacting the
protocols and general privacy of NEA.
These models assume a NEA Client resident on the Endpoint and
thus able to access privacy sensitive information. If a
Deployer wishes to support Endpoint Assessment without a NEA
Client (e.g. basing Posture on network observed behaviors) this
could improve the privacy but may limit what information is
ascertainable thus impacting flexibility of NEA Server policy.
The first model is easy to implement and deploy but has privacy
and potentially latency and scalability implications. This
approach effectively defaults the local policy to send all known
NEA Posture Attributes when an Assessment occurs. While this
might simplify deployment, it exposes a lot of information that
is potentially not relevant to the security Assessment of the
system and may introduce privacy issues. For example, is it
really important that the enterprise know whether Firefox is
being used on system instead of other browsers during the
security Posture Assessment?
The second model involves an out-of-band provisioning of the
disclosure policy to all Endpoints. This model may involve the
enterprise establishing policy that a particular list of
Attributes must be provided when a NEA exchange occurs.
Endpoint privacy policy may filter this Attribute list, but such
changes could cause the Endpoint not to be given network or
resource access. This model simplifies the network exchange as
the Endpoint always sends the filtered list of Attributes when
challenged by a particular network. However this approach
requires an out-of-band management protocol to establish and
manage the NEA disclosure policies of all system.
The third model avoids the need for pre-provisioning of
disclosure policy by allowing the NEA Server to specifically
request what Attributes are required. This is somewhat
analogous to the policy being provisioned during the NEA
exchanges so is much easier to manage. This model allows for
the NEA Server to iteratively ask for Attributes based on the
values of prior Attributes. Note, even in this model the NEA
protocols are not expected to be a general purpose query
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language, but rather allow the NEA Server to request specific
Attributes as only the defined Attributes are possible to
request. For example, an enterprise might ask about the OS
version in the initial Message Dialog and after learning the
system is a Linux system, ask for a different/smaller set of
Attributes specific to Linux then it would if the Endpoint was a
Windows system. It's envisioned that this approach might
minimize the set of Attributes sent over the network if the
Assessment is of a complex system (such as trying to understand
what patches are missing from an OS).
In each model, the User could create a set of per-network
privacy filter policies enforced by the NEA Client to prevent
the disclosure of Attributes felt to be personal in nature or
not relevant to a particular network. Such filters would
protect the privacy of the User but might result in the User not
being allowed access to the desired asset (or network) or being
provided limited access.
10. References
10.1 Normative References
[EAP] Aboba, B., Blunk, L., Vollbrecht, J., Carlson
J., and H. Levkowetz, "Extensible Authentication
Protocol (EAP)", RFC 3748, June 2004.
[HMAC] Krawczyk, H., Bellare, M., and R. Canetti,
"HMAC: Keyed-Hashing for Message
Authentication", RFC 2104, February 1997.
[IPSEC] Kent, S., Seo, K., "Security Architecture
for the Internet Protocol", RFC 4301, December
2005.
[KEYWORDS] S. Bradner, "Keywords for use in RFCs to
Indicate Requirement Levels", RFC2119 (BCP),
IETF, March 1997.
[RADIUS] Rigney, C., Willens, S., Rubens, A., and
Simpson, W., "Remote Authentication Dial In User
Service (RADIUS)", RFC 2865, June 2000.
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[TLS] Dierks, T., Rescorla, E., "The Transport Layer
Security (TLS) Protocol Version 1.1", RFC 4346,
April 2006.
10.2 Informative References
[CNAC] Cisco, Cisco's Network Admission Control Main
Web Site, http://www.cisco.com/go/nac
[NAP] Microsoft, NAP Main Web Site,
http://www.microsoft.com/nap
[TNC] Trusted Computing Group, Trusted Network Connect
Main Web Site,
https://www.trustedcomputinggroup.org/groups/net
work/
Acknowledgments
The authors of this draft would like to acknowledge the NEA working
group members who have contributed to previous requirements and
problem statement drafts that influenced the direction of this
specification: Kevin_Amorin, Diana Arroyo, Uri Blumenthal, Alan
DeKoK, Steve Hanna, Thomas Hardjono, Ravi Sahita, Mauricio Sanchez,
Jeff Six, Susan Thompson, John Vollbrecht, Nancy Winget, Han Yin,
Hao Zhou.
Authors' Addresses
Hormuzd Khosravi
Intel
2111 NE 25th Avenue
Hillsboro, OR 97124 USA
Phone: +1 503 264 0334
Email: hormuzd.m.khosravi@intel.com
Mahalingam Mani
Avaya Inc.
1033 McCarthy Blvd.
Milpitas, CA 95035 USA
Phone: +1 408 321-4840
mmani@avaya.com
Kaushik Narayan
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Cisco Systems Inc.
10 West Tasman Drive
San Jose, CA 95134
Phone: +1 408 526-8168
kaushik@cisco.com
Paul Sangster
Symantec Corporation
6825 Citrine Dr
Carlsbad, CA 92009 USA
Email: Paul_Sangster@symantec.com
Joseph Tardo
Nevis Networks
500 N. Bernardo Ave.
Mountain View, CA 94043 USA
Email: joseph.tardo@nevisnetworks.com
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