NIST SP 800-126 Rev. 1 日本語訳

Special Publication 800-126 Revision 1

Recommendations of the National Institute of Standards and Technology

David Waltermire Stephen Quinn Karen Scarfone

Computer Security Division Information Technology Laboratory National Institute of Standards and Technology Gaithersburg, MD 20899-8930

February 2011

U.S. Department of Commerce

Gary Locke, Secretary

National Institute of Standards and Technology

Dr. Patrick D. Gallagher, Director

The Information Technology Laboratory (ITL) at the National Institute of Standards and Technology (NIST) promotes the U.S. economy and public welfare by providing technical leadership for the nation‘s measurement and standards infrastructure. ITL develops tests, test methods, reference data, proof of concept implementations, and technical analysis to advance the development and productive use of information technology. ITL‘s responsibilities include the development of technical, physical, administrative, and management standards and guidelines for the cost-effective security and privacy of sensitive unclassified information in Federal computer systems. This Special Publication 800-series reports on ITL‘s research, guidance, and outreach efforts in computer security and its collaborative activities with industry, government, and academic organizations.

National Institute of Standards and Technology Special Publication 800-126, Revision 1 39 pages (Feb. 2011)

Certain commercial entities, equipment, or materials may be identified in this document in order to describe an experimental procedure or concept adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the entities, materials, or equipment are necessarily the best available for the purpose.

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The authors, David Waltermire and Stephen Quinn of the National Institute of Standards and Technology (NIST), and Karen Scarfone of G2, Inc., wish to thank their colleagues who reviewed drafts of this document and contributed to its technical content. The authors would like to acknowledge John Banghart, Harold Booth, Paul Cichonski, and Blair Heiserman of NIST; Christopher Johnson of HP Enterprise Services; Paul Bartock of the National Security Agency (NSA); Jeff Ito, Matt Kerr, Shane Shaffer, and Greg Witte of G2, Inc.; Andy Bove of SecureAcuity; Jim Ronayne of Varen Technologies; Adam Halbardier, Rhonda Farrell, Angela Orebaugh, and Victoria Thompson of Booz Allen Hamilton; Alan Peltzman of the Defense Information Systems Agency (DISA); and Jon Baker, Drew Buttner, Maria Casipe, and Charles Schmidt of the MITRE Corporation for their keen and insightful assistance throughout the development of the document.

Trademark Information

OVAL and CVE are registered trademarks, and CCE, CPE, and OCIL are trademarks, of The MITRE Corporation.

XCCDF and SCAP are trademarks of NIST.

Windows XP, Windows Vista, and Windows Server 2003 are registered trademarks of Microsoft Corporation.

All other registered trademarks or trademarks belong to their respective organizations.

Executive Summary

The Security Content Automation Protocol (SCAP) is a suite of specifications that standardize the format and nomenclature by which security software products communicate security content, particularly software flaw and security configuration information¹. SCAP is a multi-purpose protocol that supports automated configuration, vulnerability, and patch checking, technical control compliance activities, and security measurement. Goals for the development of SCAP include standardizing system security management, promoting interoperability of security products, and fostering the use of standard expressions of security content.

SCAP Version 1.1 is comprised of seven specifications—eXtensible Configuration Checklist Description Format (XCCDF), Open Vulnerability and Assessment Language (OVAL®), Open Checklist Interactive Language (OCIL), Common Platform Enumeration (CPE™), Common Configuration Enumeration (CCE™), Common Vulnerabilities and Exposures (CVE®), and Common Vulnerability Scoring System (CVSS). These specifications are grouped into three categories:

SCAP utilizes software flaw and security configuration standard reference data. This reference data is provided by the National Vulnerability Database (NVD),³ which is managed by NIST and sponsored by the Department of Homeland Security (DHS).

This publication defines the technical composition of SCAP Version 1.1 in terms of its component specifications, their interrelationships, and the requirements for SCAP content, and also describes details of how the component specifications of SCAP interoperate. The technical specification for SCAP in this publication describes the requirements and conventions that are to be employed to ensure the consistent and accurate exchange of SCAP content and the ability to reliably use the content with SCAP validated products.

The U.S. Federal Government, in cooperation with academia and private industry, is adopting SCAP and encourages its use in support of security automation activities and initiatives.⁴ SCAP has achieved widespread adoption by major software and hardware manufacturers and has become a significant component of large information security management and governance programs. The protocol is expected to evolve and expand in support of the growing needs to define and measure effective security controls, assess and monitor ongoing aspects of that information security, and successfully manage systems in accordance with risk management frameworks such as NIST Special Publication 800-535, Department of Defense (DoD) Instruction 8500.2, and the Payment Card Industry (PCI) framework.

By detailing the specific and appropriate usage of the SCAP 1.1 components and their interoperability, NIST encourages the creation of reliable and pervasive SCAP content and the development of a wide array of products that leverage SCAP capabilities.

Organizations that develop SCAP 1.1-based content or products should implement the following recommendations:

Follow the requirements listed in this document and in the associated component specifications.

Organizations should ensure that their implementation and use of SCAP 1.1 is compliant with the requirements detailed in each component specification and the information presented in this document.

If requirements are in conflict between component specifications, this document will provide clarification. If a component specification is in conflict with this document, the requirements in this document take precedence.

When creating SCAP content, adhere to the conventions specified in this document.

Security products and checklist authors assemble content from SCAP data repositories to create viable SCAP-expressed security guidance. A security configuration checklist that documents desired security configuration settings, installed patches, and other system security elements using a standardized SCAP format is known as an SCAP-expressed checklist. Such a checklist would use XCCDF to describe the checklist, CCE to identify security configuration settings to be addressed or assessed, and CPE to identify platforms for which the checklist is valid. The use of CCE and CPE entries within XCCDF checklists is an example of an SCAP convention—a requirement for valid SCAP usage. These conventions are considered part of the definition of SCAP 1.1. Organizations producing SCAP content should adhere to these conventions to ensure the highest degree of interoperability. NIST provides an SCAP Content Validation Tool that organizations can use to help validate the correctness of their SCAP content. The tool checks that SCAP content is well-formed, all cross references are valid, and required values are appropriately set.

The National Institute of Standards and Technology (NIST) developed this document in furtherance of its statutory responsibilities under the Federal Information Security Management Act (FISMA) of 2002, Public Law 107-347.

NIST is responsible for developing standards and guidelines, including minimum requirements, for providing adequate information security for all agency operations and assets; but such standards and guidelines shall not apply to national security systems. This guideline is consistent with the requirements of the Office of Management and Budget (OMB) Circular A-130, Section 8b(3), “Securing Agency Information Systems,” as analyzed in A-130, Appendix IV: Analysis of Key Sections. Supplemental information is provided in A-130, Appendix III.

This guideline has been prepared for use by Federal agencies. It may be used by nongovernmental organizations on a voluntary basis and is not subject to copyright, though attribution is desired.

Nothing in this document should be taken to contradict standards and guidelines made mandatory and binding on Federal agencies by the Secretary of Commerce under statutory authority, nor should these guidelines be interpreted as altering or superseding the existing authorities of the Secretary of Commerce, Director of the OMB, or any other Federal official.

This document provides the definitive technical specification for Version 1.1 of the Security Content Automation Protocol (SCAP). SCAP (pronounced ess-cap) consists of a suite of specifications for standardizing the format and nomenclature by which security software communicates information about software flaws and security configurations. This document defines requirements for creating and processing SCAP content. These requirements build on the requirements defined within the individual SCAP component specifications. Each new requirement pertains either to using multiple component specifications together or to further constraining one of the individual component specifications. The requirements within the individual component specifications are not repeated in this document; see those specifications to access their requirements.

The scope of this document is limited to SCAP Version 1.1. Other versions of SCAP and its component specifications, including emerging specifications, are not addressed here. Future versions of SCAP will be defined in distinct revisions of this document, each clearly labeled with a document revision number and the appropriate SCAP version number. SCAP revisions are managed through a coordinated process defined within the SCAP Release Cycle.⁶ The release cycle workflow manages changes related to SCAP specifications and validation processes including the addition of new specifications or updates to existing specifications. This process encourages community involvement, promotes transparency and awareness regarding proposed changes, and affords ample lead-time to prepare for pending changes.

This document is intended for three primary audiences:

This document assumes that readers already have general knowledge of SCAP and reasonable familiarity with the SCAP component specifications that their content, products, or services use. Individuals without this level of knowledge who would like to learn more about SCAP should consult NIST Special Publication (SP) 800-117, Guide to Adopting and Using the Security Content Automation Protocol.⁷

The remainder of this document is organized into the following major sections and appendices:

Some of the requirements and conventions used in this document reference eXtensible Markup Language (XML) content. These references come in two forms, inline and indented. An example of an inline reference is A <cpe_dict:cpe-item> may contain <cpe_dict:check> elements that reference OVAL Definitions. In this example the notation <cpe_dict:cpe-item> can be replaced by the more verbose equivalent “the XML element whose qualified name is cpe_dict:cpe-item”. An even more verbose equivalent is “the XML element in the namespace ‘http://cpe.mitre.org/dictionary/2.0‘ whose local name is cpe-item”.

An example of an indented reference is:

References to OVAL Definitions are expressed using the following format: <cpe_dict:check system= "http://oval.mitre.org/XMLSchema/oval-definitions-5" href="Oval_URL">[Oval_inventory_definition_id] </cpe_dict:check>.

The general convention used when describing XML attributes within this document is to reference the attribute as well as its associated element including the namespace alias, employing the general form "@attributeName for the <prefix:localName>".

Indented references are intended to represent the form of actual XML content. Indented references represent literal content by the use of a fixed-length font, and parametric (freely replaceable) content by the use of an italic font. Square brackets ‘[]‘ are used to designate optional content. Thus "[Oval_inventory_definition_id]" designates optional parametric content.

Both inline and indented forms use qualified names to refer to specific XML elements. A qualified name associates a named element with a namespace. The namespace identifies the specific XML schema that defines (and consequently may be used to validate) the syntax of the element instance. A qualified name declares this schema to element association using the format ‘prefix:element-name‘. The association of prefix to namespace is defined in the metadata of an XML document and generally will vary from document to document. In this specification, the conventional mappings listed in Table 1 are used. The namespace URIs in the table are not required to be resolvable; if you enter them into a web browser, for example, they may or may not work.⁸

Table 1. Conventional XML Mappings

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 Request for Comment (RFC) 2119.10

SCAP 1.1 uses the following specifications:

All references to these specifications within this document are to the version numbers listed above, unless otherwise explicitly specified.

Combinations of these specifications can be used together for particular functions, such as security configuration scanning. These functions, known as SCAP capabilities, are not product types, but rather ways in which a product can use SCAP. The collective XML content used for a capability is called an SCAP data stream, which is a specific instantiation of SCAP content. An SCAP source data stream holds the input content, and an SCAP result data stream holds the output content. The major elements of a data stream, such as the XCCDF portion or the OVAL patch portion, are referred to as stream components.

Products and organizations may want to claim conformance to one or more of the SCAP capabilities within the SCAP 1.1 specification for a variety of reasons. For example, a product may want to assert that it uses SCAP content properly and can interoperate with other products using valid SCAP content. Another example is a policy mandating that an organization use SCAP for performing vulnerability assessments and other security operations.

This section provides the high-level requirements that a product or SCAP content must meet for conformance with the SCAP 1.1 specification. Most of the requirements listed in this section reference other sections in the document that fully define the requirements.

All IT products claiming conformance with the SCAP 1.1 specification SHALL adhere to the following requirements:

Organizations creating or maintaining SCAP data streams that claim conformance with the SCAP 1.1 specification SHALL adhere to the following requirements:

This section defines the content syntax, structure, and development requirements that products and content authors and editors MUST follow to produce valid SCAP 1.1 content. This section also provides recommendations that are not mandatory; organizations are encouraged to adopt them to promote stronger interoperability and greater consistency. The first part of the section discusses SCAP source data stream requirements. The rest of the section groups requirements and recommendations by specification: XCCDF, OVAL, OCIL, CPE, CCE, CVE, and CVSS, in that order.

An SCAP data stream is a collection of XML instance documents, also called stream components. The required XML content composing an SCAP data stream depends on the use case and is designed to satisfy specific policy or situational awareness objectives. There are two types of SCAP data streams: source and result. Section 4.6 discusses SCAP result data streams, which contain the results that are generated during processing.

An SCAP source data stream is the expression of content for a specific use case using one or more stream components. For its filenames, every SCAP source data stream SHALL use a common locator prefix that is appended to the URL base of the deployed data source. Every SCAP source data stream component SHALL have a filename comprised of the locator prefix (including a trailing hyphen) followed by the appropriate component suffix, as listed in Table 2.

Table 2. SCAP Source Data Stream Conventions

For example:

file:///c:/content/example-winxp-xccdf.xml

The URL base is: file:///c:/content/ The locator prefix is: example-winxp- The stream component is: xccdf.xml

Table 2 also lists document elements. Each SCAP source data stream component SHALL use the specified element as its document element.

Each SCAP source data stream component SHALL validate against the corresponding schema and, if applicable, associated Schematron stylesheet. Each SCAP source data stream component SHOULD NOT use any constructs that are deprecated in its associated specification. Validation of each component SHALL be done in accordance with the portions of this document that define requirements for the component. NIST provides an SCAP Content Validation Tool, which is designed to help validate the correctness of an SCAP source data stream.¹² The SCAP Content Validation Tool is a simple command-line tool that will check that SCAP content is well-formed, all cross references are valid, and required values are appropriately set. All errors and warnings are returned in both XML and Hypertext Markup Language (HTML) formats.

This section lists the eXtensible Configuration Checklist Description Format (XCCDF) requirements and recommendations. They are organized by the following categories: general, <xccdf:platform>, <xccdf:Benchmark>, <xccdf:Profile>, <xccdf:Rule>, and check system usage.

The following general restrictions apply to SCAP XCCDF content:

XCCDF metadata is used by SCAP products to assist in the selection of the appropriate SCAP data stream, ensure that the most recent or correct version of an XCCDF document is used, and provide additional information about the document. The following metadata requirements and conventions apply to the <xccdf:Benchmark>, <xccdf:Profile>, <xccdf:Value>, <xccdf:Group>, and <xccdf:Rule> elements:

All remaining OPTIONAL elements in the XCCDF schema¹³ MAY be included at the author’s discretion unless otherwise noted in this document.

For all SCAP content, the applicability of <xccdf:Benchmark>, <xccdf:Profile>, <xccdf:Group>, and <xccdf:Rule> elements to specific IT platforms MAY be specified using one or more <xccdf:platform> @idref attributes. Each instance of the @idref attribute SHALL reference either a CPE Name or the @id attribute of a <cpe-lang:platform-specification/cpe-lang:platform> element.

If compound CPE Name statements are necessary, a CPE Language <cpe-lang:platform-specification> element SHALL be defined as a child of the <xccdf:Benchmark> element. The @id attribute for each <cpe-lang:platform> element declared in this manner MAY be referenced within an <xccdf:platform> element with a corresponding @idref attribute. Complex platforms MAY be referenced this way within <xccdf:Benchmark>, <xccdf:Profile>, <xccdf:Group>, and <xccdf:Rule> elements.

For example:

<cpe-lang:platform-specification> <cpe-lang:platform id="xp_and_acrobat_7.0.9"> <cpe-lang:logical-test operator="AND" negate="false"> <cpe-lang:fact-ref name="cpe:/o:microsoft:windows_xp"/> <cpe-lang:fact-ref name="cpe:/a:adobe:acrobat:7.0.9"/> </cpe-lang:logical-test> </cpe-lang:platform> </cpe-lang:platform-specification> <xccdf:platform idref="xp_and_acrobat_7.0.9"/>

Within a given <xccdf:Benchmark>, <xccdf:Profile>, <xccdf:Group>, or <xccdf:Rule> context, if no <xccdf:platform> element is defined, the <xccdf:platform> of its nearest ancestor that has an <xccdf:platform> element defined SHALL be inherited. If none of its ancestors have an <xccdf:platform> element defined, the <xccdf:Benchmark>, <xccdf:Profile>, <xccdf:Group>, or <xccdf:Rule> SHALL be considered to apply to any product.

CPE Names used within an XCCDF document SHALL match the names of existing Official CPE Dictionary¹⁴ entries where names for the desired platform exist. The matching algorithm from [CPE] to be used SHALL be CPE_Name_Match for a single CPE Name and CPE_Language_Match for a compound CPE Name. If multiple matches are found within the dictionary (e.g., deprecated and current CPE Names), the most current CPE Name SHOULD be used.

Each reference to a CPE Name SHALL be declared in the required CPE dictionary data stream component, and each OVAL inventory class definition referenced from the dictionary data stream component SHALL be specified in the required CPE inventory data stream component.

The following requirements and recommendations apply to the <xccdf:Benchmark> element:

Table 3. Use of Dublin Core Terms in XCCDF Metadata

The use of an <xccdf:Profile> element SHALL NOT be required. SCAP content commonly includes <xccdf:Profile> elements, but they are optional.

The following requirements and recommendations apply to the use of the <xccdf:check> and <xccdf:complex-check> elements:

a. The following check systems are supported by SCAP:

i. Use of the OVAL check system SHALL be indicated by the http://oval.mitre.org/XMLSchema/oval-definitions-5 system identifier.

ii. Use of the OCIL check system SHALL be indicated by the http://scap.nist.gov/schema/ocil/2 system identifier.

b. If a check system is used in XCCDF content that is not supported by SCAP, then this content SHALL NOT be considered well-formed with regards to SCAP.

If multiple <xccdf:check-content-ref> elements occur within an <xccdf:check> element, the <xccdf:check-content-ref> elements are evaluated in the order they appear. The first resolvable <xccdf:check-content-ref> element is used to determine the <xccdf:Rule> status. For each <xccdf:check-content-ref> element, an implementation attempts to retrieve the document referenced by the element‘s @href attribute. If not resolvable, the next available <xccdf:check-content-ref> element is evaluated. If none of the <xccdf:check-content-ref> elements are resolvable, then the result of the rule evaluation is the XCCDF “unchecked” status and processing of the <xccdf:Rule> ends. The @href attribute MAY map a remote URL to a local copy of the file in cases where remote access is not available, allowed, or practical.

References from SCAP compliant XCCDF to OVAL Definitions SHALL use the form:

<check-content-ref href="OVAL_Source_URI" [name="OVAL_Definition_Id"]/>

The @href attribute SHALL reference an OVAL source data stream component. When present, the @name attribute SHALL refer to a specific OVAL Definition in the designated source data stream component. Use of the @name attribute is REQUIRED except for the patches up-to-date rule, as defined in Section 3.2.6.4.

In the previous example, the <xccdf:check-content-ref> element‘s @href attribute refers to an OVAL Definition source data stream component containing one or more OVAL patch definitions. This <xccdf:check-content-ref> is equivalent to referencing a virtual OVAL Definition of the form:

<oval_definitions xmlns:oval-def="http://oval.mitre.org/XMLSchema/oval-definitions-5"> <definitions> <definition id="identifier of patch definition" version="0" class="patch">

… <criteria> <extend_definition definition_ref="identifier of patch definition 1"/> … <extend_definition definition_ref="identifier of patch definition N"/> </criteria> </definition>

</definitions> </oval_definitions>

where the extended definitions are the individual patch definitions defined in the OVAL source data stream component.

See Section 4.7.3 for additional information on mapping OVAL results to XCCDF results.

One or more <xccdf:check-export> elements MAY be used to define the binding of <xccdf:Value> elements to OVAL variables. The format of the <xccdf:check-export> element is:

<xccdf:check-export value-id="XCCDF_Value_id" export-name="OVAL_External_Variable_id"/>

The following check element example demonstrates the use of this convention:

<xccdf:check system="http://oval.mitre.org/XMLSchema/oval-definitions-5"> <xccdf:check-export value-id="NoSlowLink_var" export-name="oval:gov.nist.fdcc.xp:var:66711"/> <xccdf:check-export value-id="NoBackgroundPolicy_var" export-name="oval:gov.nist.fdcc.xp:var:66712"/> <xccdf:check-export value-id="NoGPOListChanges_var" export-name="oval:gov.nist.fdcc.xp:var:66713"/> <xccdf:check-content-ref href="fdcc-winxp-oval.xml" name="oval:gov.nist.fdcc.xp:def:6671"/> </xccdf:check>

The type and value binding of the specified XCCDF Value is constrained to match that lexical representation of the indicated OVAL Variable Data Type. Table 4 summarizes the constraints regarding data type usage. Additional information regarding OVAL and XCCDF data types can be found in the OVAL Common Schema documentation¹⁶ and the XCCDF specification [XCCDF].

Table 4. XCCDF-OVAL Data Export Matching Constraints

When referencing OCIL questionnaires as checks, XCCDF content SHALL follow all requirements defined in Appendix B of NIST Interagency Report (IR) 7692, Specifications for the Open Checklist Interactive Language (OCIL) Version 2.0 [OCIL].

The following requirements and recommendations apply to the <xccdf:Rule> element.

Each <xccdf:Rule> element SHALL include an <xccdf:ident> element containing a CVE, CCE, or CPE identifier reference if an appropriate reference exists. If the rule references an OVAL definition, then <xccdf:ident> element content SHALL match the corresponding CVE, CCE, or CPE identifier found in the associated OVAL Definition(s) if an appropriate identifier exists.

When referencing a CVE, CCE, or CPE identifier:

a. OVAL compliance class definitions reference CCE identifiers. b. OVAL inventory class definitions reference CPE identifiers. c. OVAL patch and vulnerability class definitions reference CVE identifiers.

a. The CVE system identifier, either “CVE” or “http://cve.mitre.org” (preferred method) b. The CCE system identifier, either “CCE” or “http://cce.mitre.org” (preferred method) c. The CPE system identifier, either “CPE” or “http://cpe.mitre.org” (preferred method)

For example:

<Rule id="AuditAccountLogonEvents"> … <ident system="http://cce.mitre.org">CCE-3867-0</ident> … </Rule>

An <xccdf:ident> element referencing a CVE, CCE, or CPE identifier SHALL be ordered before other <xccdf:ident> elements referencing non-SCAP identifiers. Identifiers from previous revisions of CCE or CPE MAY also be specified following the SCAP identifiers.

If an <xccdf:Rule> element references a specific OVAL Definition, then:

An XCCDF rule MAY reference an OCIL questionnaire. This SHOULD be done only for cases where OVAL cannot perform the check.

An OVAL instance document MAY be used to represent a series of checks to verify that patches have been installed. Historically, an XCCDF convention has been used to identify such a reference. An XCCDF benchmark MAY include a patches up-to-date rule that references an OVAL patch source data stream component. When implementing a patches up-to-date XCCDF rule, the following approach SHALL be used:

For example:

<Rule id="security_patches_up_to_date" selected="false"> <title>Security Patches Up-To-Date</title> <description>Keep systems up to current patch levels</description> <check system="http://oval.mitre.org/XMLSchema/oval-definitions-5">

<check-content-ref href="scap-win2000-patches.xml"/> </check>

</Rule>

SCAP 1.0 required the inclusion of static CVSS scores in XCCDF vulnerability-related rules. However, CVSS base scores sometimes change over time, such as when more information is available about a particular vulnerability, and CVSS temporal and environmental scores are intended to change to reflect current threats, security controls, and other factors. Current CVSS scores acquired dynamically, such as from a data feed, SHOULD be used in place of static CVSS scores in the @weight attribute within XCCDF vulnerability-related rules. Section 3.8 contains additional requirements for CVSS usage.

While the default version¹⁷ of OVAL used in SCAP 1.1 SHALL be OVAL version 5.8, content authors SHOULD utilize the earliest SCAP-supported version of OVAL (5.3 at minimum) that includes all required tests and is necessary to properly address the content's purpose or use case. This approach, often referred to as the “least-version-principle”, allows for SCAP content to remain viable over a longer period of time by allowing for the broadest support within products, while reducing the content maintenance burden that would be required to maintain revisions of content for multiple specification versions.

All of the OVAL content MUST contain an <oval:generator> element. The version of any particular document instance SHALL be specified using the <oval:schema_version> content element of the <oval:generator> as in this example:

<oval:generator> <oval:product_name>The OVAL Repository</oval:product_name> <oval:schema_version>5.8</oval:schema_version> </oval:generator>

The version of an <oval-var:oval_variables> document SHALL be the same as that of the <oval-def:oval_definitions> document whose external variables are bound by the variables document.

The following requirements apply to particular classes of OVAL definitions:

a. If an OVAL compliance class definition maps to one or more CCE identifiers, the definition SHOULD include <oval-def:reference> elements that reference those identifiers using the following format:

<oval-def:reference source="http://cce.mitre.org" ref_id="CCE_identifier"/>

The source attribute SHALL be defined using either “CCE” or “http://cce.mitre.org” (preferred method).

b. Definitions that are directly or indirectly extended SHALL be limited to inventory and compliance classes.

a. If an OVAL inventory class definition maps to one or more CPE identifiers, the definition SHOULD include <oval-def:reference> elements that reference those identifiers using the following format:

<oval-def:reference source="http://cpe.mitre.org" ref_id="CPE_identifier"/>

The source attribute SHALL be defined using either “CPE” or “http://cpe.mitre.org” (preferred method).

b. Definitions that are directly or indirectly extended SHALL be limited to the inventory class.

a. If an OVAL patch class definition maps to one or more CVE identifiers, the definition MAY include <oval-def:reference> elements that reference those identifiers using the following format:

<oval-def:reference source="http://cve.mitre.org" ref_id="CVE_identifier"/>

The source attribute SHALL be defined using either “CVE” or “http://cve.mitre.org” (preferred method).

b. If an OVAL patch class definition is associated with a source specific identifier (for example, Knowledge Base numbers for Microsoft patches), these identifiers SHOULD be included in <oval-def:reference> elements contained by the definition. For example:

<oval-def:reference source="www.microsoft.com/Patch" ref_id="KB912919"/>

c. Definitions that are directly or indirectly extended SHALL be limited to inventory and patch classes.

a. If an OVAL vulnerability class definition maps to one or more CVE identifiers, the definition SHOULD include <oval-def:reference> elements that reference those identifiers using the following format:

<oval-def:reference source="http://cve.mitre.org" ref_id="CVE_identifier"/>

The source attribute SHALL be defined using either “CVE” or “http://cve.mitre.org” (preferred method).

b. Definitions that are directly or indirectly extended SHALL be limited to inventory and vulnerability classes.

OCIL content SHOULD be used for checking rules that cannot be fully automated with OVAL.¹⁸ For example, a particular software product may not have an application programming interface (API) that supports OVAL use. Another example is performing a check that requires user interaction, such as asking the user to look up information within a management console or to report a serial number affixed to a computing device. OCIL can also be used to collect a user‘s own information, such as whether the user participated in a recent security training session.

The Official CPE Dictionary data feed¹⁹ MAY be used by SCAP components to reference CPE Names. Local enumerations are permitted, but if a CPE Name for a product or platform exists in the Official CPE Dictionary, the content SHALL match the product or platform referenced by that official identifier.

Section 8 of [CPE] provides the defining structure of the Official CPE Dictionary. For certain names, a <cpe_dict:cpe-item> MAY contain one or more <check> elements that reference OVAL system inventory definitions using the following format: <cpe_dict:check system="http://oval.mitre.org/XMLSchema/oval-definitions-5" [href="oval_URL"]>oval_inventory_definition_id</cpe_dict:check>

For example:

<cpe-list xmlns="http://cpe.mitre.org/dictionary/2.0"

xmlns:cpe_dict="http://cpe.mitre.org/dictionary/2.0">

<cpe-item name="cpe:/o:microsoft:windows_2003"> <title>Microsoft Windows Server 2003</title> <check system=http://oval.mitre.org/XMLSchema/oval-definitions-5

href="example-winsvr2003-oval.xml"> oval:org.mitre.oval:def:128

</check> </cpe-item> </cpe-list>

The referenced OVAL inventory definition SHALL specify the technical procedure for determining whether or not a specific target asset is an instance of the CPE Name specified by the <cpe_dict:cpe-item> element. This usage is encouraged for a CPE dictionary source data stream component.

If a <cpe_dict:cpe-item> contained in a CPE dictionary data stream component references an OVAL “inventory” definition, then that definition SHALL be resolved by an @href attribute referencing a CPE Inventory source data stream component in the same data stream. Furthermore, the title of the

<cpe_dict:cpe-item> SHALL match the title of an affected platform bound to the referenced definition.

To maintain consistency and accuracy among SCAP content, SCAP content referencing a configuration setting SHALL use the official CCE identifier if a CCE entry for a particular configuration setting exists in the Official CCE Dictionary. If no CCE exists for the configuration setting of interest, the content author SHOULD seek to have a CCE identifier issued for the configuration setting. See the OVAL compliance class definition requirements in Section 3.3 and the <xccdf:ident> requirements in Section 3.2.6.1 for additional requirements involving CCE identifier references.

The MITRE Corporation maintains the current official CCE list at http://cce.mitre.org/lists/cce_list.html and new CCEs can be requested from the CCE Content Team at http://cce.mitre.org/lists/creation_process.html.

Use of an official, dynamic data feed is preferred to static coding of values in SCAP data sources. The NVD provides a data feed²⁰ that correlates CCE identifiers with the control identifiers described in NIST SP 800-53. Embedding control identifiers within SCAP content is strongly discouraged due to the maintenance burden that it imposes on content maintainers when the control identifiers are revised.

CVE references in SCAP content MAY include both “candidate” and “entry” status identifiers. The use of deprecated CVE identifiers SHALL NOT be allowed.

If a CVE identifier exists for a particular vulnerability, the official CVE identifier SHALL be used. If no CVE exists for the software flaw, an alternate identifier MAY be used, but the user SHOULD seek to have a CVE identifier issued for the vulnerability. The process for submitting unpublished vulnerabilities and obtaining CVE identifiers is available from The MITRE Corporation via http://cve.mitre.org/cve/obtain_id.html.

NIST provides a CVE data feed to support dynamic and current vulnerability information and associated metadata (e.g., CVSS values). The current schema is available at http://nvd.nist.gov/download.cfm.

The NIST CVE data feed, discussed in Section 3.7, is one source of CVSS base score and vector data that MAY be used by products to support additional use cases built on SCAP usage. In support of these additional use cases, CVSS base scores and vectors from this data feed MAY be used by products along with temporal, and environmental scores and vectors from other sources.

Additional information on CVSS use is available in NIST IR 7435, The Common Vulnerability Scoring System (CVSS) and Its Applicability to Federal Agency Systems (http://csrc.nist.gov/publications/PubsNISTIRs.html#NIST-IR-7435).

This section defines the processing requirements that tools MUST follow in order to correctly process SCAP 1.1 content. This section also provides recommendations that are not mandatory; organizations are encouraged to adopt them to promote stronger interoperability and greater consistency. The topics covered in this section are legacy support, SCAP content validation, the <xccdf:Profile> element, and check system usage. The end of the section covers result-related topics: SCAP result data streams, XCCDF results, OVAL results, and OCIL results.

Products supporting SCAP 1.1 SHALL process SCAP 1.0 content as described under the SCAP 1.0 version of NIST SP 800-126.21

Products supporting OVAL SHALL support OVAL Definition documents written against OVAL versions 5.3, 5.4, 5.5, 5.6, 5.7, and 5.8.

Within the OVAL Language, constructs may be deprecated.²² Deprecated constructs MUST be handled properly during OVAL Definition evaluation. Similar to the requirement to support previous minor versions of OVAL, this requirement will ensure that content that made use of these deprecated constructs continues to be supported in SCAP.

An SCAP implementation that can import SCAP content SHALL be capable of validating the content against the appropriate schemas and Schematron stylesheets, detecting and reporting errors, and failing gracefully if there are errors.

If an <xccdf:Profile> element is not provided or selected, then profile processing SHALL be skipped and standard XCCDF benchmark processing rules SHALL apply.²³

When evaluating an <xccdf:platform> element in XCCDF content, it is necessary to evaluate machine state to determine the presence of a referenced CPE on the machine. CPEs referenced in an <xccdf:platform> element directly or by a <cpe-lang:fact-ref> contained within a referenced <cpe-lang:platform-specification> element SHALL be evaluated as follows:

In XCCDF content, if multiple <xccdf:check-content-ref> elements are provided, then the following evaluation method SHALL be performed:

Use of XCCDF check systems as specified in the <xccdf:check> element’s @system attribute SHALL be restricted as follows:

An <xccdf:check-content-ref> element may omit the @name attribute only for a patches up-to-date rule (see Section 3.2.6.4). When processing a patches-up-to-date rule, only OVAL patch class definitions SHALL be evaluated; all other classes of definitions (e.g., inventory class definitions) SHALL NOT be evaluated.

An SCAP result data stream contains the results of the evaluation of one or more SCAP source data streams by an SCAP product. Correlation and aggregation products such as security awareness incident response tools may consume properly formatted SCAP result data streams to support organizational reporting requirements.

For its filenames, every SCAP result data stream SHALL use two common locator prefixes that are appended to the URL base of the deployed result file. The first locator prefix (a string followed by a hyphen) SHALL be associated with a specific result data stream. The first locator prefix SHALL be consistent between multiple evaluations of the same source content. The second locator prefix (a string followed by a hyphen) MAY be used to differentiate among similar result data streams.

Every SCAP result data stream component SHALL have a filename comprised of the first locator prefix, the second locator prefix, and the appropriate component suffix (as listed in Table 5), in that order. Each component SHALL use the element specified in Table 5 as its document element.

Table 5. SCAP Result Data Stream Naming Conventions

Each XCCDF result data stream component SHALL comply with the XCCDF Results schema.

XCCDF test results SHALL be documented as the contents of an <xccdf:TestResult> element that either stands alone as the root of an XML document or is embedded as a child-element of an <xccdf:Benchmark> root element. In the former case, the <xccdf:TestResults> document requires an embedded <xccdf:benchmark> element that identifies the associated benchmark. In the latter case, the associated benchmark is the embedding benchmark; <xccdf:benchmark> elements SHALL be ignored in <xccdf:TestResult> elements that are embedded in their associated benchmark.

To be considered valid SCAP result content, the following conditions SHALL be met:

a. If no <xccdf:Profile> was selected, then the <xccdf:Profile> SHALL be omitted.

b. When using a profile during the processing of XCCDF content, the test results SHALL embed an <xccdf:profile> element that contains the name of the utilized profile.

c. Reported rule results SHALL include all selected rules within the specified Profile.

d. Reported value-settings SHALL include all those values that are exported by the reported rules. The specific settings are those determined by the reported Profile.

a. The @idref attribute of the <xccdf:rule-result> SHALL identify the selected rule.

b. If an evaluated rule references a check system (e.g., OVAL, OCIL) that the SCAP implementation does not support, the implementation SHALL return a result of “notchecked” for each such rule.

c. The <xccdf:check/xccdf:check-content-ref> element SHALL record the reference to the check system specific result file and check name within the result file using the @href and @name attributes, respectively. This approach provides traceability between XCCDF and check results.

Table 6. XCCDF Fact Descriptions

The <xccdf:rule-result> element provides data indicating the result of assessing a system using the identified <xccdf:Rule> element. If the target <xccdf:Rule> identified by the <xccdf:rule-result idref=""> attribute has one or more <ident> elements with the “http://cve.mitre.org” or “CVE” system identifiers, then each <xccdf:ident> element SHALL also appear within the <xccdf:rule-result> element.

For example:

<xccdf:rule-result idref="java-upgrade-278" weight="10.0"> <xccdf:result>pass</xccdf:result> … <xccdf:ident system="http://cve.mitre.org">CVE-2006-0614</xccdf:ident> … </xccdf:rule-result>

An <xccdf:rule-result> of “pass” SHALL indicate that the target platform satisfies all the conditions of the XCCDF rule and is unaffected by the vulnerability or exposure referenced by the CVE.

The <xccdf:rule-result> element provides data indicating the result of assessing a system using the identified <xccdf:Rule> element. If the target <xccdf:Rule> identified by the <xccdf:rule-result> @idref attribute has one or more <xccdf:ident> elements with the “http://cce.mitre.org” or “CCE” system identifiers, then each <xccdf:ident> element SHALL also appear within the <rule-result> element. For example:

<xccdf:rule-result idref="minimum_password_length"> <xccdf:result>pass</xccdf:result> … <xccdf:ident system="http://cce.mitre.org">CCE-2981-9</xccdf:ident> … </xccdf:rule-result>

An <xccdf:rule-result> of “pass” SHALL indicate that the target platform complies with the configuration setting guidance expressed in the XCCDF rule.

When evaluating an <xccdf:Rule> element that references an OVAL Definition, the <xccdf:rule-result> element SHALL be used to capture the result of this evaluation. This result SHALL be determined by evaluating the referenced OVAL Definition on a target host. The <xccdf:result> value recorded SHALL be mapped from the OVAL Definition Result produced during evaluation.

While the OVAL specification permits limiting result status reporting, SCAP-compliant content SHALL include full status reporting including Error, Unknown, Not Applicable, Not Evaluated, True, and False.

SCAP compliant processors that generate XCCDF <xccdf:rule-result> elements SHALL apply the mapping illustrated in Table 7 when deriving <xccdf:Rule> results from OVAL Definition processing. The corresponding <xccdf:rule-result/xccdf:result> value SHALL be recorded based on the @class of the OVAL Definition where applicable.

Table 7. Deriving XCCDF Rule Results from OVAL Definition Results

The mappings in Table 7 are specific to each OVAL Definition class. For example, if an OVAL Definition of class “compliance” is processed and the XCCDF returns a result of “true”, the product is conveying the fact that the system was found to be compliant with that check and therefore returns a “pass” result. A similar definition for a vulnerable condition will return results of “false” if that vulnerability was not found on the examined devices, resulting in a “pass” from the XCCDF rule.

If the <xccdf:Rule> under evaluation has an <xccdf:check-content-ref> element with the @name attribute omitted, then the result of each evaluated OVAL Definition SHALL be recorded as a separate <xccdf:rule-result>. This will commonly occur for a “security_patches_up_to_date” check, as defined in Section 3.2.6.4. In this case the <xccdf:rule-result/xccdf:check-content-ref> SHALL identify the specific check result of each evaluated OVAL definition using the @href and @name attributes as described in Section 4.7, item 8c. .

Each SCAP OVAL result data stream component SHALL use the <oval-res:oval_results> element as the document element. Each OVAL result data stream component SHALL validate against version 5.8 of the OVAL Results schema²⁴ regardless of the version of the OVAL Definitions document that was evaluated.

An SCAP OVAL result data stream component SHALL include the results of every OVAL Definition used to generate the reported results.

In order to be SCAP compliant, an SCAP scanning product SHALL be able to produce all the types of OVAL Results output described below. The specific result output SHALL be configurable within the SCAP product.

In order to support SCAP instances where OVAL thin content (only the ID of the definition and the results) is preferred, SCAP products SHALL support all valid values for the <oval-res:directives> controlling the expected content of the results file.

To support the ability for results to be consumed by the appropriate product(s), data results SHALL be expressed as Single Machine Without System Characteristics, Single Machine With System Characteristics, or Single Machine With Thin Results as follows:

For this format, the values for the <oval-res:directives> element SHALL be: <oval-res:definition_true content="full" reported="true"/> <oval-res:definition_false content="full" reported="true"/> <oval-res:definition_unknown content="full" reported="true"/> <oval-res:definition_error content="full" reported="true"/> <oval-res:definition_not_evaluated content="full" reported="true"/> <oval-res:definition_not_applicable content="full" reported="true"/>

For this format, the values for the <oval-res:directives> element SHALL be: <oval-res:definition_true content="full" reported="true"/> <oval-res:definition_false content="full" reported="true"/> <oval-res:definition_unknown content="full" reported="true"/> <oval-res:definition_error content="full" reported="true"/> <oval-res:definition_not_evaluated content="full" reported="true"/> <oval-res:definition_not_applicable content="full" reported="true"/>

When creating the OVAL System Characteristics as defined by the <oval-sc:oval_system_characteristics> element, the <oval-sc:collected_objects> and <oval-sc:system_data> elements SHALL be provided.

For this format, the values for the <oval-res:directives> element SHALL be: <oval-res:definition_true content="thin" reported="true"/> <oval-res:definition_false content="thin" reported="true"/> <oval-res:definition_unknown content="thin" reported="true"/> <oval-res:definition_error content="thin" reported="true"/> <oval-res:definition_not_evaluated content="thin" reported="true"/> <oval-res:definition_not_applicable content="thin" reported="true"/>

An SCAP OCIL result data stream component SHALL include the results of every OCIL questionnaire, test_action, and question used to generate the reported results.

This section discusses additional requirements for four common types of SCAP content: compliance checking, vulnerability scanning, inventory scanning, and OVAL-only scanning.

SCAP content can be used to compare system characteristics and settings against an SCAP-expressed checklist in an automated fashion. This can verify that operating systems and applications comply with security checklists and identify any deviations from those checklists.

The SCAP source data stream component that MUST be included for compliance checking is the XCCDF Benchmark, which expresses the checklist. Each rule in the XCCDF Benchmark SHALL reference one of the following:

Each XCCDF Benchmark SHALL have at least one rule that references either an OVAL compliance definition in the OVAL Compliance component or an OCIL questionnaire in the OCIL Questionnaire component.

All OVAL Compliance, OCIL Questionnaire, and OVAL Patch components referenced by the XCCDF Benchmark SHALL be included in the SCAP source data stream.

If the XCCDF Benchmark component references any CPE names, then the SCAP source data stream MUST include the following components, in addition to those already mentioned:

SCAP content can be used to scan operating systems and applications to look for known software flaws that introduce security exposures. The content enables consistent detection and reporting of these flaws.

The SCAP source data stream component that MUST be included for vulnerability scanning is the XCCDF Benchmark, which expresses the checklist of the flaws to be checked for. Each rule in the XCCDF Benchmark SHALL reference one of the following:

Each XCCDF Benchmark SHALL have at least one rule that references either an OVAL vulnerability definition in the OVAL Vulnerability component or an OCIL questionnaire in the OCIL Questionnaire component.

All OVAL Vulnerability, OCIL Questionnaire, and OVAL Patch components referenced by the XCCDF Benchmark SHALL be included in the SCAP source data stream.

If the XCCDF Benchmark component references any CPE names, then the SCAP source data stream MUST include the following components, in addition to those already mentioned:

SCAP content can be used to collect information on the software installed on systems. One example of how this could be used is to verify that a group of systems all have required security software programs installed. This could help verify compliance with technical security control requirements. Another example is to collect software inventory data on devices that are not directly connected to the enterprise network, such as smart phones.

The SCAP source data stream components that MUST be included for inventory scanning are:

OVAL content can be used on its own, without XCCDF Benchmarks or other components, to perform scanning. The only SCAP source data stream component that MUST be included is an OVAL component that maps to the desired definition classes (e.g., compliance class for configuration setting checks, inventory class for asset checks, patch class for patch presence checks, vulnerability class for software flaw vulnerability presence checks). The mapping SHALL correspond to the mappings defined in Section 3.2.6.2.

Selected acronyms and abbreviations used in the guide are defined below.

API — Application Programming Interface

CCE — Common Configuration Enumeration

CPE — Common Platform Enumeration

CVE — Common Vulnerabilities and Exposures

CVSS — Common Vulnerability Scoring System

DHS — Department of Homeland Security

DoD — Department of Defense

FDCC — Federal Desktop Core Configuration

FISMA — Federal Information Security Management Act

IR — Interagency Report

IT — Information Technology

ITL — Information Technology Laboratory

NIST — National Institute of Standards and Technology

NSA — National Security Agency

NVD — National Vulnerability Database

OCIL — Open Checklist Interactive Language

OMB — Office of Management and Budget

OS — Operating System

OVAL — Open Vulnerability and Assessment Language

PCI — Payment Card Industry

RFC — Request for Comments

SCAP — Security Content Automation Protocol

SP — Service Pack

SP — Special Publication

URI — Uniform Resource Identifier

URL — Uniform Resource Locator

XCCDF — eXtensible Configuration Checklist Description Format

XML — eXtensible Markup Language

The following normative references are pointers to the specifications, schema, dictionaries, and other information that are required to implement the SCAP 1.1 components:

[CCE] CCE specification and description http://scap.nist.gov/revision/1.1/index.html#cce

[CPE] CPE specification and description http://scap.nist.gov/revision/1.1/index.html#cpe

[CVE] CVE specification and description http://scap.nist.gov/revision/1.1/index.html#cve

[CVSS] CVSS specification and description http://scap.nist.gov/revision/1.1/index.html#cvss

[OCIL] OCIL specification and description http://scap.nist.gov/revision/1.1/index.html#ocil

[OVAL] OVAL specification and description http://scap.nist.gov/revision/1.1/index.html#oval

[XCCDF] XCCDF specification and description http://scap.nist.gov/revision/1.1/index.html#xccdf