RFC 5209
Network Endpoint Assessment (NEA): Overview and Requirements
Pages: 53
Informational
Informational
Part 2 of 3 – Pages 10 to 34
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 identifies the major
functionality of the NEA Client and Server and their relationships, as well as the protocols they use to communicate at various levels (e.g., PA is carried by the PB protocol). While the diagram shows 3 layered protocols, it is envisioned that PA is likely a thin message wrapper around a set of attributes and that it is batched and encapsulated in PB. PB is primarily a lightweight message batching protocol, so the protocol stack is mostly the transport (PT). 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 mechanisms for discovery of NEA Clients and NEA Servers. It is expected that NEA Clients and NEA Servers are configured with information that allows 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 in the specifications of candidate protocols such as the Posture Transport (PT) protocol.
5.1. NEA Client and Server
5.1.1. NEA Client
The NEA Client is resident on an endpoint device and comprised of the following functionality: o Posture Collector(s) o Posture Broker Client o Posture Transport Client(s) The NEA Client is responsible for responding to requests for attributes describing the configuration of the local operating domain of the client and handling the assessment results including potential remediation instructions for how to conform to policy. A NEA Client is not responsible for reporting on the posture of entities that might exist on the endpoint or over the network that are outside the domain of execution (e.g., in other virtual machine domains) of the NEA Client. For example, a network address translation (NAT) device might route communications for many systems behind it, but when the NAT device joins the network, its NEA Client would only report its own (local) posture. Similarly, endpoints with virtualization capabilities might have multiple independent domains of execution (e.g., OS instances). Each NEA Client is only responsible for reporting posture for its domain of execution, but this information might be aggregated by other local mechanisms to represent the posture for multiple domains on the endpoint. Such posture aggregation mechanisms are outside the focus of this specification. Endpoints lacking NEA Client software (which is out of NEA scope) or choosing not to provide the attributes required by the NEA Server could be considered non-compliant. The NEA model includes capabilities to enable the endpoint to update its contents in order to become compliant.5.1.1.1. Posture Collector
The Posture Collector is responsible for responding to requests for posture information in Request Attributes from the NEA Server. The Posture Collector is also responsible for handling assessment decisions in Result Attributes and remediation instructions in Remediation Attributes. A single NEA Client can have several Posture Collectors capable of collecting standard and/or vendor-specific Posture Attributes for particular features of the endpoint. Typical
examples include Posture Collectors that provide information about
Operating System (OS) version and patch levels, anti-virus software,
and security mechanisms on the endpoint such as host-based Intrusion
Detection System (IDS) or firewall.
Each Posture Collector will be associated with one or more
identifiers that enable it to be specified as the destination in a PA
message. The Posture Broker Client uses these identifiers to route
messages to this Collector. An identifier might be dynamic (e.g.,
generated by the Posture Broker Client at run-time during
registration) or more static (e.g., pre-assigned to the Posture
Collector at install-time and passed to the Posture Broker Client
during registration) or a function of the attribute messages the
Collector desires to receive (e.g., message type for subscription).
The NEA model allocates the following responsibilities to the Posture
Collector:
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 particular
features of the endpoint and returning this information in
Posture Attributes.
- Caching and recognizing the applicability of recently issued
attributes containing reusable assertions that might serve to
prove compliance and returning this attribute instead of
posture information.
o Receiving attributes containing remediation instructions on how
to update functionality on the endpoint. This could require the
Collector to interact with the user, owner, and/or a remediation
server.
o Monitoring the posture of (a) particular features(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. Note that this is not a set of requirements for what each Posture Collector implementation must support, nor is it an exhaustive list of all the things a Posture Collector may do.5.1.1.2. Posture Broker Client
The Posture Broker Client is both a PA message multiplexer and a de-multiplexer. The Posture Broker Client is responsible for de-multiplexing the PB message received from the NEA Server and distributing each encapsulated PA message 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 receiving a request for particular attributes from 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) 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 Posture Broker Client also handles the global assessment decision from the Posture Broker Server and may interact with the user to communicate the global assessment decision and aid in any necessary remediation steps. The NEA model allocates the following responsibilities to the Posture Broker Client: o Maintaining a registry of known Posture Collectors and allowing for Posture Collectors to dynamically register and deregister. 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 reassessment. o Providing user notification about the global assessment decision and other user messages sent by the NEA Server.
5.1.1.3. Posture Transport Client
The Posture Transport Client is 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 supporting different transport protocols (e.g., 802.1X, VPN). 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: o Initiating and maintaining the communication channel to the NEA Server. The Posture Transport Client hides the details of the underlying carrier that 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 is typically comprised of the following NEA functionality: o Posture Validator(s) o Posture Broker Server o Posture Transport Server(s) The Posture Validators might 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 responsible for handling Posture Attributes from corresponding Posture Collector(s). A Posture Validator can handle Posture Attributes from one or more Posture Collectors and vice-versa. The Posture Validator performs the posture assessment for one or more features of the endpoint (e.g., anti-virus software) and creates the result and, if necessary, the remediation instructions, or it may choose to request additional attributes from one or more Collectors.
Each Posture Validator will be associated with one or more
identifiers that enable it to be 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.,
generated by the Posture Broker Server at run-time during
registration) or more static (e.g., pre-assigned to a Posture
Validator at install-time and passed to the Posture Broker Server
during registration) or a function of the attribute messages the
Validator desires to receive (e.g., message type for subscription).
Posture Validators can be co-located on the NEA Server or can be
hosted on separate servers. A particular NEA Server is likely to
need to handle multiple Posture Validators.
The NEA model allocates the following responsibilities to the Posture
Validator:
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 for particular
functionality on the endpoint.
o Receiving attributes from the Posture Collector. The response
from the Posture Collector may include:
- Posture Attributes collected for the requested functionality.
- Assertion Attributes that indicate the compliance result from
a prior assessment.
o Assessing the posture of endpoint features based on the
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:
- Result Attributes that communicate the posture assessment
result.
- Remediation Attributes that communicate the remediation
instructions to the Posture Collector.
o Monitoring out-of-band updates that trigger reassessment and
require notifications to be sent to the Posture Broker Server.
o Providing cryptographic protection for attributes sent to the
Posture Collector and offering cryptographic verification of the
attributes received from the Posture Collector.
The above list describes the model's view of the possible
responsibilities of the Posture Validator. Note that this is not a
set of requirements for what each Posture Validator implementation
must support, nor is it an exhaustive list of all the things a
Posture Validator may do.
5.1.2.2. Posture Broker Server
The Posture Broker Server acts as a multiplexer and a de-multiplexer
for attribute messages. The Posture Broker Server parses the PB
messages received from the NEA Client and de-multiplexes them into PA
messages that it passes to the associated Posture Validators. The
Posture Broker Server multiplexes the PA messages (e.g., messages
containing (a) Request Attribute(s) from the relevant Posture
Validator(s)) into one or more PB messages and sends them to the NEA
Client via the Posture Transport protocol. The quantity and ordering
of Posture Validator responses (PA messages) and global assessment
decision multiplexed into the PB response message(s) can be
determined by the Posture Broker Server 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 assessment decision based on individual posture assessment
results from the various Posture Validators. This global assessment
decision is sent back to the NEA Client in Result Attributes within a
PB message. A particular NEA Server 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:
o Maintaining a registry of Posture Validators and allowing for
Posture Validators to register and deregister.
o Multiplexing and de-multiplexing posture messages from and to
the relevant Posture Validators.
o Computing the global assessment decision based on posture
assessment results from the various Posture Validators and
compliance policy. This assessment decision is sent to the
Posture Broker Client in a PB message.
5.1.2.3. Posture Transport Server
The Posture Transport Server is 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 Server on a particular NEA Server to support different transport protocols. 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: 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 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)
PA is a protocol that carries one or more attributes between Posture Collectors and their associated Posture Validator. The PA protocol is a message-oriented lightweight wrapper around a set of attributes being exchanged. This wrapper may indicate the purpose of attributes within the message. Some of the types of messages expected include: requests for posture information (Request Attributes), posture information about the endpoint (Posture Attributes), results of an assessment (Result Attributes), reusable compliance assertions (Assertion Attributes), and instructions to remediate non-compliant portions of the endpoint (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 Posture Collectors on the NEA Client and the corresponding Posture Validators on the NEA Server involved in a particular assessment. The PB protocol provides 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 assessment decision in the Result Attribute from the Posture Broker Server to the Posture Broker Client. PB may be used to carry additional types of messages for use by the Posture Broker Client and Server (e.g., information about user preferred interface settings such as language).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) transport(s) PB messages during the network connection request or after network connectivity has been established. In scenarios where an initial assessment needs to occur during the network connection, the PT protocol (e.g., EAP within 802.1X) may have constrained use of the network, so deployments may choose to limit the amount and/or size of the attributes exchanged. The NEA Client and NEA Server should be able to detect when a potentially constrained situation exists prior to the assessment based upon properties of the underlying network protocol. Using this information, NEA policy could dictate what aspects of the endpoint to include in the initial assessment and potentially limit the PA message attributes exchanged. This could be followed up by a full reassessment after the endpoint is placed on the network. Alternatively, deployments can choose not to limit their assessment by configuring their network access technology to temporarily grant restricted IP connectivity prior to the assessment and use an unconstrained, high bandwidth IP-based transport during the assessment. Some of the constraints that may exist for protocols involved in the network connection phase include: o Limited maximum transmission unit (MTU) size and ability to negotiate larger MTUs, o Inability to perform multiple roundtrips, o Lack of support for piggybacking attributes for other protocols,
o Low bandwidth or high latency limitations precluding exchanges
of large amounts of data,
o Inability of servers to initiate messages except during the
network connection phase.
The PT protocol selection process needs to consider the impact of
selecting a particular PT and set of underlying protocols on the
deployment needs of PA and PB. PA and PB will be selected prior to
PT so the needs of PA and PB will be known. Certain underlying
protocol stacks may be too constrained to support adequate NEA
assessments during network connection.
The PT protocol provides reliable message delivery, mutual
authentication, and cryptographic protection for the PB messages as
specified by local policy.
5.3. Attributes
The PA protocol is responsible for the exchange of attributes between
a Posture Collector and Posture Validator. The PB protocol may also
carry the global assessment decision attributes from the Posture
Broker Server. 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 obtained. The NEA WG will define a common
(standard) set of attributes that are expected to be widely
applicable to Posture Collectors and thus used for maximum
interoperability, but Posture Collectors may support additional
vendor-specific attributes when necessary.
Depending on the deployment scenario, the purpose of the attributes
exchanged may be different (e.g., posture information vs. asserted
compliance). This section discusses the originator and expected
situation resulting in the use of each classification of attributes
in a PA message. These classifications are not intended to dictate
how the NEA WG will specify the attributes when defining the
attribute namespace or schema.
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 host-based 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 stating recent prior compliance to policy in hopes of avoiding the need to recollect the posture and send it to the NEA Server. Examples of assertions include (a) NEA Server provided attributes (state) describing a prior evaluation (e.g., opaque to endpoint, signed, time stamped items stating specific results) or (b) 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 in addition to, Posture Attributes.5.3.2. Attributes Normally Sent by NEA Server:
o Request Attributes - Attributes that 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. 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 through just the global assessment decision. o Remediation Attributes - Attributes that explain 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 assessment decision was that the endpoint is not currently compliant. Remediation and Result Attributes may both exist within a NEA Server attribute message. o Assertion Attributes - Attributes containing NEA Server assertions of compliance to a policy for future use by the NEA Client. See section 5.3.1 for more information.
6. Use Cases
This section discusses several of the NEA 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 impact the NEA protocols. We broadly classify the use cases into two categories, each with its 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 evaluation might be triggered by a request to join a network, a request to use a service, or a desire to understand the posture of a system. o Reassessment - evaluation of the posture of an endpoint that has previously been assessed. This evaluation could occur for a variety of reasons including the NEA Client or Server recognizing an occurrence affecting the endpoint that might raise the endpoint's risk level. This could be as simple as it having been a long time since the endpoint's prior reassessment.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 do not qualify for this category of use case if they 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 its posture evaluated again.6.1.1. Triggered by Network Connection or Service Request
This use case focuses on assessments performed at the time an endpoint attempts to join a network or request use of a service that requires a posture evaluation. 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 or service.
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 threats on the network. A variety of types of endpoint actions could result in this class of assessment. For example, an assessment could be triggered by the endpoint trying to access a highly protected network service (e.g., financial or HR application server) where heightened security checking is required. A better known example could include requesting entrance to a network that requires systems to meet compliance policy. This example is discussed in more detail in the following section.6.1.1.1. Example
An IT employee returning from vacation boots his office desktop computer that 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 NEA Server determines that the system is lacking a recent security patch designed to fix a serious vulnerability and the system is placed on a restricted access network. The desktop follows the provided remediation instructions to download and install the necessary patch. Later, the desktop requests again to join the network and this time is provided full access to the enterprise network after a full assessment.6.1.1.2. Possible Flows and Protocol Usage
The following describes typical message flows through the NEA reference model for this example use case: 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 instructed to assess the endpoint joining the wired network. 3. Based upon compliance policy, the Posture Broker Server contacts the operating system patch, host-based firewall, and anti-virus Posture Validators to request the necessary posture. Each Posture Validator creates a PA message containing the desired attributes to be requested for assessment from the desktop system.
4. The Posture Broker Server aggregates the PA messages from the
Posture Validators into a PB message. The Posture Broker
Server passes the PB message to the Posture Transport Server
that uses the PT protocol to send the PB message to the NEA
Client on the desktop computer.
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 the PA messages with the requests for attributes to
the firewall, operating system 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 attributes that are authorized in a
PA message to the Posture Broker Client.
8. The Posture Broker Client aggregates these PA messages into a
single PB message and sends it to the Posture Broker Server
using the Posture Transport Client to Server session.
9. The Posture Transport Server provides the PB message to the
Posture Broker Server that de-multiplexes the message and sends
the appropriate attributes to the corresponding Posture
Validator.
10. Each Posture Validator compares the values of the attributes it
receives with the expected values defined in its policy.
11. The anti-virus and firewall Posture Validators return
attributes to the Posture Broker Server stating the desktop
computer is compliant, but the operating system patch Posture
Validator returns non-compliant. The operating system patch
Posture Validator creates a PA message that contains attributes
with remediation instructions in addition to the attribute
indicating non-compliance result.
12. The Posture Broker Server aggregates the PA messages and sends
them in a PB message to the Posture Broker Client via the
Posture Transport Server and Posture Transport Client.
13. The Posture Broker Client delivers the PA messages with the
results from the various Posture Validators to the Posture
Collectors including the PA message containing attributes with
remediation instructions to the operating system patch Posture
Collector. This Posture Collector then interacts with the user
to download and install the needed patches, potentially while
the endpoint remains quarantined.
14. Upon completion of the remediation, the above steps 1-10 are
repeated (triggered by the NEA Client repeating its request to
join the network).
15. This time each involved Posture Validator (including the
operating system patch Posture Validator) returns a compliant
status and the Posture Broker Server returns a compliant result
indicating a global success.
16. The Posture Broker Client receives the compliant result 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 attributes containing posture information
o NEA Server sends remediation instructions
o NEA Client causes a reassessment after remediation
6.1.2. Triggered by Endpoint
This use case highlights that an endpoint (possibly at the request of
a user) may wish to trigger an assessment of its posture to determine
whether its security protective mechanisms are running and up to
date.
6.1.2.1. 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 she requests a posture
assessment. The NEA Server performs an initial assessment of the system and determines it is 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.6.1.2.2. 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 that causes an assessment to be triggered. 3. The Posture Broker Server detects the new session and consults policy to determine that Posture Validators to involve in the assessment. The Posture Broker Server decides to employ several Posture Validators including the anti-virus Posture Validator. 4. The Posture Validators involved create PA messages containing requests for particular attributes containing information about the desired terminal room computer based on the school's security policy. 5. The Posture Broker Server assembles a PB message including each of the PA messages from the Posture Validators. 6. The Posture Transport Server sends the PB message to the Posture Transport Client where it is passed on to the Posture Broker Client. 7. The Posture Broker Client on the student's computer de-multiplexes the PA messages and delivers them to the corresponding Posture Collectors. 8. 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 the requested posture to the Posture Broker Client.
9. 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.
10. The Posture Broker Server separates and distributes the Posture
Collector PA messages to the associated Posture Validators.
11. The Posture Validators determine whether the attributes
containing the posture included in the PA message are compliant
with their policies and returns a posture assessment decision
to the Posture Broker Server. In this case, the anti-virus
Posture Validator returns a PA message indicating a
non-compliant result because the anti-virus software is not
running and includes attributes describing how to activate the
software.
12. The Posture Broker Server determines the overall compliance
decision based on all of the Validators' assessment results and
sends a PB message containing an attribute expressing the
global assessment decision and the anti-virus Validator's PA
message. In this case, the global assessment decision
indicates the system is compliant (despite the anti-virus
Validator's result) 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 was
the case according to the other Posture Validators).
13. The Posture Transport Server sends the PB message to the
Posture Transport Client that provides the message to the
Posture Broker Client.
14. The Posture Broker Client on the terminal room computer
examines the PB message's global assessment decision attribute
and reports to the student that the system was deemed to be
compliant, but that an advisory was included.
15. The Posture Broker Client provides the PA message with the
remediation attributes to the anti-virus Posture Collector that
interacts with the user to explain how to turn on anti-virus to
improve the local protections.
16. The student turns on the anti-virus software and on completion
steps 1-10 are repeated.
17. This time the anti-virus Posture Validator returns a success
status and the Posture Broker Server returns a successful
global assessment decision in the PB message.
18. The Posture Broker Client receives the successful global
assessment decision in the PB message and the student now uses
the computer for her assignment.
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.
o Voluntary endpoint requested initial assessment,
o Successful (compliant) global assessment decision included in PB
message with a PA message containing an advisory set of
attributes for remediation.
6.2. Posture Reassessment
Reassessment(s) of endpoints can happen anytime after being admitted
to the network after a successful initial NEA assessment. These
reassessments 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 on the NEA Server. They may also be periodic (timer-
driven) to reassess the health of the endpoint.
6.2.1. Triggered by NEA Client
This use case allows for software on the endpoint or a user to
determine that a reassessment of the system is required. There are a
variety of reasons why such a reassessment 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 NEA Server 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 reassessment of the firewall compliance. The
NEA Server returns a decision that the firewall must be reactivated
to stay on the network. The NEA Client explains the decision to the
user and how to reactivate the firewall. The HR person restarts the
firewall and initiates a request to rejoin 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 that typically might act as a Posture Collector triggers the Posture Broker Client to initiate a posture reassessment. The Posture Broker Client creates a PB message that contains a PA message indicating the desktop firewall has been disabled. 2. The Posture Broker Client sends the PB message to the Posture Broker Server. 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 PA message to the firewall Posture Validator for evaluation. 5. The firewall Posture Validator determines that the endpoint is no longer compliant because its firewall has been disabled. 6. The Posture Validator generates a PA message that contains attributes indicating a non-compliant posture assessment result and remediation instructions for how to reactivate the firewall. 7. The Posture Validator communicates the PA message with the posture assessment result to the Posture Broker Server to respond back to the NEA Client. 8. The Posture Broker Server generates a PB message including a global assessment decision of non-compliant and the 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 attribute containing the global assessment decision received from the NEA Server and displays the non-compliance messages to the user.
11. The Posture Broker Client forwards the PA message to the
firewall Posture Collector; the Posture Collector displays the
remediation instructions for how to enable the desktop
firewall.
12. The user is prompted to initiate a reassessment after
completing the remediation.
13. Upon completion of the remediation, the NEA Client reinitiates
a request for reassessment 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 Posture Broker Server generates a PB message with a global
assessment decision 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.
o Voluntary, endpoint (software) initiated posture reassessment
request
o NEA Server requests specific firewall-oriented Posture
Attributes
o NEA Client (firewall Posture Collector) interacts with user to
remediate problem
6.2.2. Triggered by NEA Server
In many cases, especially for reassessment, the NEA Server may
initiate specific or complete reassessment of one or more endpoints
triggered by:
o Time (periodic)
o Event occurrence
o Policy updates
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 them to be installed by 5 PM. This policy change causes the NEA Server to request a reassessment to determine which endpoints are impacted and lacking the patches. The marketing employee's laptop is reassessed and determined to need the patches. A remediation advisory is sent and presented to the employee explaining how to obtain the patches and that they must be installed by 5 PM. The marketing employee immediately downloads and installs the patches and obtains an assertion that all patches are now installed. At 5 PM, the enterprise performs another reassessment of all impacted endpoints to determine if they are now in compliance. The marketing employee's laptop is reassessed and presents the assertion that it has the patches installed and thus is determined to be compliant.6.2.2.2. Possible Flows and Protocol Usage
The following describes the message flows through the NEA reference model for the above example: 1. Marketing employee joins network and completes an initial assessment resulting in a compliant decision. 2. The Enterprise Administrator configures an operating system patch policy indicating that recent patches are required on all endpoints by 5 PM to prevent serious vulnerabilities. 3. The NEA Server's operating system patch Posture Validator becomes aware of this policy change and creates a PA message requesting attributes describing OS patches in use and triggers the Posture Broker Server to initiate a posture reassessment of all endpoints connected to the network. 4. The Posture Broker creates a PB message that includes the PA message from the operating system patch Posture Validator. 5. The Posture Broker Server gradually establishes a session 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 operating system patch Posture Collector.
9. The operating system patch Posture Collector determines the OS
patches present on the endpoint and if authorized by its
disclosure policy creates a PA message containing the patch
information attributes.
10. The Posture Broker Client sends a PB message that includes the
operating system patch PA message.
11. The Posture Transport Client transports the PB message to the
Posture Transport Server where it is passed to the Posture
Broker Server.
12. The Posture Broker Server receives the PB message and delivers
the PA message to the operating system patch Posture Validator.
13. The operating system patch Posture Validator extracts the
attributes describing the current OS patches 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.
14. The Posture Validator generates a PA message that includes
attributes stating the posture assessment decision is
non-compliant and attributes containing the remediation
instructions to enable the endpoint to download the required OS
patches.
15. The Posture Validator communicates the posture assessment
result to the Posture Broker Server along with its PA message.
16. The Posture Broker Server generates a global assessment
decision and sends a PB message with the decision and the
operating system patch Posture Validator's PA message.
17. The Posture Transport Server transports the PB message to the
Posture Transport Client where it is passed to the Posture
Broker Client.
18. The Posture Broker Client processes the Result Attribute
received from the NEA Server and displays the non-compliance
decision to the user.
19. The Posture Broker Client forwards the PA message containing
the remediation instructions to the operating system patch
Posture Collector; the Posture Collector guides the user with
instructions on how to become compliant that include
downloading the appropriate OS patches to prevent the
vulnerability.
20. The marketing employee installs the required patches and now is
in compliance.
21. The NEA Client triggers a reassessment of the operating system
patches that causes a repeat of many of the steps above. This
time, in step 13 the operating system patch Posture Validator
determines the marketing employee's laptop is compliant. It
returns a reusable (e.g., signed and dated) set of attributes
that assert OS patch compliance to the latest policy. These OS
patch compliance assertions can be used in a future PA message
from the operating system patch Collector instead of
determining and providing the specific patch set posture as
before.
22. This time when the operating system patch Posture Collector
receives the PA message that contains reusable attributes
asserting compliance, it caches those attributes for future
use.
23. Later at 5 PM, the NEA Server triggers a gradual reassessment
to determine compliance to the patch advisory. When the
operating system patch Posture Collector receives the request
for posture information (like in step 9 above) it returns the
cached set of assertions (instead of specific OS patch
information) to indicate that the patches have been installed
instead of determining all the patches that have been installed
on the system.
24. When the operating system patch Posture Validator receives the
PA message containing the assertions, it is able to determine
that they are authentic and acceptable assertions instead of
specific posture. It 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 reassessment required due to urgent patch
availability
o NEA Client submits reusable assertion attributes instead of
posture that patch is installed
o NEA Server capable of recognizing previously issued assertion
attributes are sufficient instead of posture
(page 34 continued on part 3)