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Versions: 00 01                                                         
Security Automation and Continuous Monitoring                   M. Cokus
Internet-Draft                                                 D. Haynes
Intended status: Informational                             D. Rothenberg
Expires: March 11, 2017                            The MITRE Corporation
                                                             J. Gonzalez
                                         Department of Homeland Security
                                                       September 7, 2016


                        OVAL(R) Variables Model
               draft-haynes-sacm-oval-variables-model-01

Abstract

   This document specifies Version 5.11.1 of the OVAL Variables Model
   which contains constructs that allow for the specification of values
   for external_variables defined in content that was created using the
   OVAL Definitions Model.  The OVAL Variables Model serves as a useful
   mechanism for parameterizing content based on the OVAL Definitions
   Model.

Status of This Memo

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

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

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

   This Internet-Draft will expire on March 11, 2017.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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



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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  oval_variables  . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  VariablesType . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  VariableType  . . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  OVAL Variables Model Schema . . . . . . . . . . . . . . . . .   4
   6.  Intellectual Property Considerations  . . . . . . . . . . . .   8
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   10. Change Log  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     10.1.  -00 to -01 . . . . . . . . . . . . . . . . . . . . . . .   9
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     11.1.  Normative References . . . . . . . . . . . . . . . . . .   9
     11.2.  Informative References . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   The Open Vulnerability and Assessment Language (OVAL) [OVAL-WEBSITE]
   is an international, information security community effort to
   standardize how to assess and report upon the machine state of
   systems.  For over ten years, OVAL has been developed in
   collaboration with any and all interested parties to promote open and
   publicly available security content and to standardize the
   representation of this information across the entire spectrum of
   security tools and services.

   OVAL provides an established framework for making assertions about an
   system's state by standardizing the three main steps of the
   assessment process: representing the current machine state; analyzing
   the system for the presence of the specified machine state; and
   representing the results of the assessment which facilitates
   collaboration and information sharing among the information security
   community and interoperability among tools.

   This draft is part of the OVAL contribution to the IETF SACM WG that
   standardizes the representation used to analyze a system for the
   presence of a specific machine state.  It is intended to serve as a
   starting point for the endpoint posture assessment data modeling




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   needs of SACM specifically for creating parameterized Collection and
   Evaluation Guidance.

1.1.  Requirements Language

   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 RFC 2119 [RFC2119].

2.  oval_variables

   The oval_variables type defines the base structure in the OVAL
   Variables Model for representing a collection of OVAL Variables and
   their associated values.  This container type adds metadata about the
   origin of the content and allows for a signature.

   +-----------+--------------------+-------+--------------------------+
   | Property  | Type               | Count | Description              |
   +-----------+--------------------+-------+--------------------------+
   | generator | oval:GeneratorType | 1     | Information regarding    |
   |           |                    |       | the generation of the    |
   |           |                    |       | OVAL Variables content.  |
   |           |                    |       | The timestamp property   |
   |           |                    |       | of the generator MUST    |
   |           |                    |       | represent the time at    |
   |           |                    |       | which the oval_variables |
   |           |                    |       | was created.             |
   |           |                    |       |                          |
   | variables | VariablesType      | 1     | The variables defined in |
   |           |                    |       | the OVAL Variables       |
   |           |                    |       | content.                 |
   |           |                    |       |                          |
   | signature | ext:Signature      | 0..1  | Mechanism to ensure the  |
   |           |                    |       | integrity and            |
   |           |                    |       | authenticity of the OVAL |
   |           |                    |       | Variables content.       |
   +-----------+--------------------+-------+--------------------------+

                     Table 1: oval_variables Construct

3.  VariablesType

   The VariablesType provides a container for one or more OVAL
   Variables.







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   +----------+--------------+-------+---------------------------------+
   | Property | Type         | Count | Description                     |
   +----------+--------------+-------+---------------------------------+
   | variable | VariableType | 1..*  | A collection of OVAL Variables. |
   +----------+--------------+-------+---------------------------------+

                     Table 2: VariablesType Construct

4.  VariableType

   The VariableType defines a variable in the OVAL Variables Model that
   corresponds to an instance of an external variable in content based
   on the OVAL Definitions Model.

   +----------+--------------------------------+-------+---------------+
   | Property | Type                           | Count | Description   |
   +----------+--------------------------------+-------+---------------+
   | id       | oval:VariableIDPattern         | 1     | The globally  |
   |          |                                |       | unique        |
   |          |                                |       | identifier of |
   |          |                                |       | an external   |
   |          |                                |       | variable.     |
   |          |                                |       |               |
   | datatype | oval:SimpleDatatypeEnumeration | 1     | The datatype  |
   |          |                                |       | of the        |
   |          |                                |       | value(s) in   |
   |          |                                |       | the variable. |
   |          |                                |       |               |
   | comment  | string                         | 1     | The           |
   |          |                                |       | documentation |
   |          |                                |       | associated    |
   |          |                                |       | with the      |
   |          |                                |       | variable      |
   |          |                                |       | instance.     |
   |          |                                |       |               |
   | value    | string                         | 1..*  | The value(s)  |
   |          |                                |       | associated    |
   |          |                                |       | with the      |
   |          |                                |       | variable.     |
   +----------+--------------------------------+-------+---------------+

                      Table 3: VariableType Construct

5.  OVAL Variables Model Schema

   The XML Schema that implements this OVAL Variables Model can be found
   below.




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           <?xml version="1.0" encoding="utf-8"?>
   <xsd:schema
     xmlns:xsd="http://www.w3.org/2001/XMLSchema"
     xmlns:oval="http://oval.mitre.org/XMLSchema/oval-common-5"
     xmlns:oval-var="http://oval.mitre.org/XMLSchema/
     oval-variables-5"
     xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
     xmlns:sch="http://purl.oclc.org/dsdl/schematron"
     targetNamespace="http://oval.mitre.org/XMLSchema/
     oval-variables-5"
     elementFormDefault="qualified" version="5.11">
     <xsd:import
       namespace="http://oval.mitre.org/XMLSchema/oval-common-5"
       schemaLocation="oval-common-schema.xsd"/>
     <xsd:import
       namespace="http://www.w3.org/2000/09/xmldsig#"
       schemaLocation="xmldsig-core-schema.xsd"/>
     <xsd:annotation>
       <xsd:documentation/>
       <xsd:documentation>The following is a
         description of the elements, types, and
         attributes that compose the core schema for
         encoding Open Vulnerability and Assessment
         Language (OVAL) Variables. This schema is
         provided to give structure to any external
         variables and their values that an OVAL
         Definition is expecting.</xsd:documentation>
       <xsd:appinfo>
         <schema>Core Variable</schema>
         <version>5.11.1</version>
         <date>4/22/2015 09:00:00 AM</date>
         <terms_of_use>Copyright (C) 2010 United States Government.
           All Rights Reserved.</terms_of_use>
         <sch:ns prefix="oval-var"
           uri="http://oval.mitre.org/XMLSchema/oval-variables-5"
         />
       </xsd:appinfo>
     </xsd:annotation>
   <!-- ====================================================== -->
   <!-- ====================================================== -->
   <!-- ====================================================== -->
     <xsd:element name="oval_variables">
       <xsd:annotation>
         <xsd:documentation>The oval_variables
           element is the root of an OVAL Variable
           Document. Its purpose is to bind together
           the different variables contained in the
           document. The generator section must be



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           present and provides information about
           when the variable file was compiled and
           under what version. The optional Signature
           element allows an XML Signature as defined
           by the W3C to be attached to the document.
           This allows authentication and data
           integrity to be provided to the user.
           Enveloped signatures are supported. More
           information about the official W3C
           Recommendation regarding XML digital
           signatures can be found at
           http://www.w3.org/TR/xmldsig-core/.</xsd:documentation>
       </xsd:annotation>
       <xsd:complexType>
         <xsd:sequence>
           <xsd:element name="generator"
             type="oval:GeneratorType"/>
           <xsd:element name="variables"
             type="oval-var:VariablesType"
             minOccurs="0" maxOccurs="1"/>
           <xsd:element ref="ds:Signature"
             minOccurs="0" maxOccurs="1"/>
         </xsd:sequence>
       </xsd:complexType>
       <xsd:key name="varKey">
         <xsd:annotation>
           <xsd:documentation>Enforce uniqueness
             amongst the variable ids found in the
             variable document.</xsd:documentation>
         </xsd:annotation>
         <xsd:selector xpath=".//oval-var:variable"/>
         <xsd:field xpath="@id"/>
       </xsd:key>
     </xsd:element>
   <!-- ====================================================== -->
   <!-- ==================  GENERATOR  ======================= -->
   <!-- ====================================================== -->
     <!--
                   The GeneratorType is defined by the oval common
                   schema.  Please refer to that documentation for a
                   description of the complex type.
           -->
   <!-- ====================================================== -->
   <!-- =================  DEFINITIONS  ====================== -->
   <!-- ====================================================== -->
     <xsd:complexType name="VariablesType">
       <xsd:annotation>
         <xsd:documentation>The VariablesType complex



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           type is a container for one or more
           variable elements. Each variable element
           holds the value of an external variable
           used in an OVAL Definition. Please refer
           to the description of the VariableType for
           more information about an individual
           variable.</xsd:documentation>
       </xsd:annotation>
       <xsd:sequence>
         <xsd:element name="variable"
           type="oval-var:VariableType" minOccurs="1"
           maxOccurs="unbounded"/>
       </xsd:sequence>
     </xsd:complexType>
     <xsd:complexType name="VariableType">
       <xsd:annotation>
         <xsd:documentation>Each variable element
           contains the associated datatype and value
           which will be substituted into the OVAL
           Definition that is referencing this
           specific variable.</xsd:documentation>
         <xsd:documentation>The notes section of a
           variable should be used to hold
           information that might be helpful to
           someone examining the technical aspects of
           the variable. Please refer to the
           description of the NotesType complex type
           for more information about the notes
           element.</xsd:documentation>
       </xsd:annotation>
       <xsd:sequence>
         <xsd:element name="value"
           type="xsd:anySimpleType" minOccurs="1"
           maxOccurs="unbounded"/>
         <xsd:element name="notes"
           type="oval:NotesType" minOccurs="0"
           maxOccurs="1"/>
       </xsd:sequence>
       <xsd:attribute name="id"
         type="oval:VariableIDPattern" use="required"/>
       <xsd:attribute name="datatype" use="required"
         type="oval:SimpleDatatypeEnumeration">
         <xsd:annotation>
           <xsd:documentation>Note that the 'record'
             datatype is not permitted on
             variables.</xsd:documentation>
         </xsd:annotation>
       </xsd:attribute>



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       <xsd:attribute name="comment"
         type="xsd:string" use="required"/>
     </xsd:complexType>
   <!-- ====================================================== -->
   <!-- ==================  SIGNATURE  ======================= -->
   <!-- ====================================================== -->
     <!--
                   The signature element is defined by the xmldsig
                   schema.  Please refer to that documentation for
                   a description of the valid elements and types.
                   More information about the official W3C
                   Recommendation regarding XML digital
                   signatures can be found at
                   http://www.w3.org/TR/xmldsig-core/.
           -->
   <!-- ====================================================== -->
   <!-- ====================================================== -->
   <!-- ====================================================== -->
   </xsd:schema>


6.  Intellectual Property Considerations

   Copyright (C) 2010 United States Government.  All Rights Reserved.

   DHS, on behalf of the United States, owns the registered OVAL
   trademarks, identifying the OVAL STANDARDS SUITE and any component
   part, as that suite has been provided to the IETF Trust.  A "(R)"
   will be used in conjunction with the first use of any OVAL trademark
   in any document or publication in recognition of DHS's trademark
   ownership.

7.  Acknowledgements

   The authors wish to thank DHS for sponsoring the OVAL effort over the
   years which has made this work possible.  The authors also wish to
   thank the original authors of this document Jonathan Baker, Matthew
   Hansbury, and Daniel Haynes of the MITRE Corporation as well as the
   OVAL Community for its assistance in contributing and reviewing the
   original document.  The authors would also like to acknowledge Dave
   Waltermire of NIST for his contribution to the development of the
   original document.

8.  IANA Considerations

   This memo includes no request to IANA.





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9.  Security Considerations

   While OVAL is just a set of data models and does not directly
   introduce security concerns, it does provide a mechanism by which to
   represent endpoint posture assessment information.  This information
   could be extremely valuable to an attacker allowing them to learn
   about very sensitive information including, but, not limited to:
   security policies, systems on the network, criticality of systems,
   software and hardware inventory, patch levels, user accounts and much
   more.  To address this concern, all endpoint posture assessment
   information should be protected while in transit and at rest.
   Furthermore, it should only be shared with parties that are
   authorized to receive it.

   Another possible security concern is due to the fact that content
   expressed as OVAL has the ability to impact how a security tool
   operates.  For example, content may instruct a tool to collect
   certain information off a system or may be used to drive follow-up
   actions like remediation.  As a result, it is important for security
   tools to ensure that they are obtaining OVAL content from a trusted
   source, that it has not been modified in transit, and that proper
   validation is performed in order to ensure it does not contain
   malicious data.

10.  Change Log

10.1.  -00 to -01

   There are no textual changes associated with this revision.  This
   revision simply reflects a resubmission of the document so that it
   remains in active status.

11.  References

11.1.  Normative References

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

11.2.  Informative References

   [OVAL-WEBSITE]
              The MITRE Corporation, "The Open Vulnerability and
              Assessment Language", 2015,
              <http://ovalproject.github.io/>.




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Authors' Addresses

   Michael Cokus
   The MITRE Corporation
   903 Enterprise Parkway, Suite 200
   Hampton, VA  23666
   USA

   Email: msc@mitre.org


   Daniel Haynes
   The MITRE Corporation
   202 Burlington Road
   Bedford, MA  01730
   USA

   Email: dhaynes@mitre.org


   David Rothenberg
   The MITRE Corporation
   202 Burlington Road
   Bedford, MA  01730
   USA

   Email: drothenberg@mitre.org


   Juan Gonzalez
   Department of Homeland Security
   245 Murray Lane
   Washington, DC  20548
   USA

   Email: juan.gonzalez@dhs.gov















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