= OpenSCAP User Manual
:imagesdir: ./images
:workbench_url: https://www.open-scap.org/tools/scap-workbench/
:sce_web:       https://www.open-scap.org/features/other-standards/sce/
:openscap_web: https://open-scap.org/
:oscap_git:     https://github.com/OpenSCAP/openscap
:devel_manual:  https://github.com/OpenSCAP/openscap/blob/maint-1.3/docs/developer/developer.adoc
:ssg_git:       https://github.com/OpenSCAP/scap-security-guide
:xmlsec:        https://www.aleksey.com/xmlsec/
:xslt:          http://www.w3.org/TR/xslt
:xsl:           http://www.w3.org/Style/XSL/
:ssg:   http://open-scap.org/security-policies/scap-security-guide/
:xccdf: http://scap.nist.gov/specifications/xccdf/
:xccdf_1-2: http://scap.nist.gov/specifications/xccdf/#resource-1.2
:scap:  http://scap.nist.gov/
:nist:  http://www.nist.gov/
:cpe:   https://cpe.mitre.org/
:cce:   https://cce.mitre.org/
:oval:  https://oval.mitre.org/
:pci_dss: https://www.pcisecuritystandards.org/security_standards/
:usgcb: http://usgcb.nist.gov/
:stig:    http://iase.disa.mil/stigs/Pages/index.aspx
:scap_1-3: https://csrc.nist.gov/Projects/Security-Content-Automation-Protocol/SCAP-Releases/scap-1-3
:scap_1-2: https://csrc.nist.gov/Projects/Security-Content-Automation-Protocol/SCAP-Releases/SCAP-1-2
:scap_1-1: https://csrc.nist.gov/Projects/Security-Content-Automation-Protocol/SCAP-Releases/SCAP-1-1
:scap_1-0: https://csrc.nist.gov/Projects/Security-Content-Automation-Protocol/SCAP-Releases/SCAP-1-0
:nvd:       https://web.nvd.nist.gov/view/ncp/repository
:toc:
:toclevels: 4
:toc-placement: preamble
:numbered:
:footer-style: none

image::vertical-logo.png[align="center"]

toc::[]

== Introduction

This documentation provides information about OpenSCAP and its most common
operations. With OpenSCAP, you can check security configuration settings of a
system, and examine the system for signs of a compromise by using rules based on
standards and specifications. 

OpenSCAP uses {scap}[SCAP] which is a line of specifications maintained by the
{nist}[NIST]. SCAP was created to provide a standardized approach for
maintaining system security. New specifications are governed by NIST's SCAP
http://scap.nist.gov/timeline.html[Release cycle] in order to provide a
consistent and repeatable revision workflow. OpenSCAP mainly processes the
{xccdf}[XCCDF] which is a standard way of expressing a checklist content and
defines security checklists. It also combines with other specifications such as
{cpe}[CPE], {cce}[CCE] and {oval}[OVAL] to create a SCAP-expressed checklist
that can be processed by SCAP-validated products. For more information about the
SCAP please refer to http://open-scap.org/features/standards/[SCAP Standards].

OpenSCAP supports SCAP {scap_1-3}[1.3] and is backward compatible with SCAP
{scap_1-2}[1.2], SCAP {scap_1-1}[1.1] and SCAP {scap_1-0}[1.0]. No special
treatment is required to import and process earlier versions of the SCAP
content.

If you want to perform configuration or vulnerability scans of a local system
then the following must be available:

. A tool (`oscap` or SCAP Workbench)
. SCAP content (SCAP source data stream, XCCDF, OVAL...)

The `oscap` tool is a part of the {openscap_web}[OpenSCAP] project. If you're
interested in a graphical alternative to this tool please visit
{workbench_url}[SCAP Workbench] page.

We will use the {ssg}[SCAP Security Guide] project to provide us the SCAP
content. It provides security policies written in a form of SCAP documents
covering many areas of security compliance, and it implements security guidances
recommended by respected authorities, namely {pci_dss}[PCI DSS], {stig}[STIG],
and {usgcb}[USGCB].

You can also generate your own SCAP content if you have an understanding of at
least XCCDF or OVAL. XCCDF content is also frequently published online under
open source licenses, and you can customize this content to suit your needs
instead. SCAP Workbench is a great tool to do the customization.

== Installing OpenSCAP

You can either build OpenSCAP from {oscap_git}[source code] or you can use an
existing build for your Linux distribution. 

For instructions about building from source code, please refer to
{devel_manual}[OpenSCAP Developer Manual].

To install OpenSCAP on Red Hat Enterprise Linux 8 and newer, on CentOS 8 and
newer or on Fedora use the following command:

----
# dnf install openscap-scanner
----

To install OpenSCAP on Red Hat Enterprise Linux 7 or CentOS 7 or older use the
following command:

----
# yum install openscap-scanner
----

To install OpenSCAP on Debian or Ubuntu use the following command:

----
# apt install libopenscap8
----

After the installation is completed you can start using the `oscap` command line
tool.

To display the version of OpenSCAP, supported specifications, built-in CPE
names, and supported OVAL objects, type the following command:

----
$ oscap --version
----

=== Getting SCAP content

To perform any task with OpenSCAP you also need to have security policies in
SCAP format. We call them *SCAP content*. There are many providers of SCAP
content.

In this document we will use SCAP content provided by *SCAP Security Guide*
(SSG). Many Linux distributions ship it in the `scap-security-guide` package.

To install `scap-security-guide` on Red Hat Enterprise Linux 8 and newer, on
CentOS 8 and newer or on Fedora use the following command:

----
# yum install scap-security-guide
----

To install `scap-security-guide`  on Red Hat Enterprise Linux 7 or CentOS 7 or
older use the following command:

----
# yum install scap-security-guide
----

The SCAP content will be installed in the `/usr/share/xml/scap/ssg/content/`
directory.

On other platforms, you can download the upstream release from
https://github.com/ComplianceAsCode/content/releases/[GitHub].

When the SCAP content is installed on your system, `oscap` can
process the content by specifying the file path to the content.

You can also use any other SCAP content with OpenSCAP.

== Displaying information about SCAP content

Information about an SCAP file can be displayed using the `oscap info` command.

=== Displaying information about SCAP source data streams

The most common SCAP file type is an SCAP source data stream. In the following
example, we will display information about SCAP source data stream
`/usr/share/xml/scap/ssg/content/ssg-rhel8-ds.xml` from the
`scap-security-guide` package.

----
$ oscap info /usr/share/xml/scap/ssg/content/ssg-rhel8-ds.xml
Document type: Source Data Stream
Imported: 2021-01-12T04:50:11

Stream: scap_org.open-scap_datastream_from_xccdf_ssg-rhel8-xccdf-1.2.xml
Generated: (null)
Version: 1.3
Checklists:
	Ref-Id: scap_org.open-scap_cref_ssg-rhel8-xccdf-1.2.xml
		Status: draft
		Generated: 2021-01-12
		Resolved: true
		Profiles:
			Title: CIS Red Hat Enterprise Linux 8 Benchmark
				Id: xccdf_org.ssgproject.content_profile_cis
			Title: Unclassified Information in Non-federal Information Systems and Organizations (NIST 800-171)
				Id: xccdf_org.ssgproject.content_profile_cui
			Title: Australian Cyber Security Centre (ACSC) Essential Eight
				Id: xccdf_org.ssgproject.content_profile_e8
			Title: Health Insurance Portability and Accountability Act (HIPAA)
				Id: xccdf_org.ssgproject.content_profile_hipaa
			Title: PCI-DSS v3.2.1 Control Baseline for Red Hat Enterprise Linux 8
				Id: xccdf_org.ssgproject.content_profile_pci-dss
			Title: [DRAFT] DISA STIG for Red Hat Enterprise Linux 8
				Id: xccdf_org.ssgproject.content_profile_stig
			Title: Protection Profile for General Purpose Operating Systems
				Id: xccdf_org.ssgproject.content_profile_ospp
		Referenced check files:
			ssg-rhel8-oval.xml
				system: http://oval.mitre.org/XMLSchema/oval-definitions-5
			ssg-rhel8-ocil.xml
				system: http://scap.nist.gov/schema/ocil/2
			security-data-oval-com.redhat.rhsa-RHEL8.xml
				system: http://oval.mitre.org/XMLSchema/oval-definitions-5
Checks:
	Ref-Id: scap_org.open-scap_cref_ssg-rhel8-oval.xml
	Ref-Id: scap_org.open-scap_cref_ssg-rhel8-ocil.xml
	Ref-Id: scap_org.open-scap_cref_ssg-rhel8-cpe-oval.xml
	Ref-Id: scap_org.open-scap_cref_security-data-oval-com.redhat.rhsa-RHEL8.xml
Dictionaries:
	Ref-Id: scap_org.open-scap_cref_ssg-rhel8-cpe-dictionary.xml
----

* **Document type** describes what format the file is in. Common types include
XCCDF, OVAL, source data stream and result data stream.
* **Imported** is the date the file was imported for use with OpenSCAP. Since
OpenSCAP uses the local filesystem and has no proprietary database format
the imported date is the same as file modification date.
* **Stream** is the data stream ID.
* **Version** is the version of the SCAP standard.
* **Checklists** lists available checklists incorporated in the data stream that
you can use for the `--benchmark-id` command line attribute with `oscap xccdf
eval`. Also each checklist has the detailed information printed.
* **Status** is the XCCDF Benchmark status. Common values include "accepted",
"draft", "deprecated" and "incomplete". Please refer to the XCCDF specification
for details.
* **Generated** date is the date the file was created or generated. This date is
shown for XCCDF files and Checklists and is sourced from the XCCDF **Status**
element.
* **Profiles** lists available profiles, their titles and IDs that you can use for
the `--profile` command line attribute.
* **Checks** and **Dictionaries** lists OVAL checks components and CPE
dictionaries components in the given data stream.

To display more detailed information about a profile including the profile
description, use the `--profile` option followed by the profile ID.

----
$ oscap info --profile xccdf_org.ssgproject.content_profile_ospp /usr/share/xml/scap/ssg/content/ssg-rhel8-ds.xml
----

=== Displaying information about SCAP result data streams

The `oscap info` command is also helpful with other SCAP file types such as
SCAP result data stream (ARF) files.

OpenSCAP can display the evaluation start and end dates when given ARF file.

In this example, we will display information about the ARF file `arf.xml`.

----
$ oscap info arf.xml 
Document type: Result Data Stream
Imported: 2021-02-11T11:04:51

Asset: asset0
	ARF report: xccdf1
		Report request: collection1
		Result ID: xccdf_org.open-scap_testresult_xccdf_org.ssgproject.content_profile_ospp
		Source benchmark: /usr/share/xml/scap/ssg/content/ssg-fedora-ds.xml
		Source profile: xccdf_org.ssgproject.content_profile_ospp
		Evaluation started: 2021-02-11T11:03:06+01:00
		Evaluation finished: 2021-02-11T11:04:51+01:00
		Platform CPEs:
			cpe:/o:fedoraproject:fedora:25
			cpe:/o:fedoraproject:fedora:26
			cpe:/o:fedoraproject:fedora:27
----

== Scanning

The main goal of OpenSCAP is to perform configuration and vulnerability scans of
a local system. OpenSCAP is able to evaluate SCAP source data streams, XCCDF
benchmarks and OVAL definitions and generate the appropriate results.

SCAP content can be provided either in a single file (as an SCAP source data
stream), or as multiple separate XML files.

=== Scanning using SCAP source data streams

Commonly, all required input files are bundled together in an SCAP source data
stream. Scanning using an SCAP source data stream can be performed by the
`oscap xccdf eval` command, with some additional parameters available.
The basic syntax of the `oscap xccdf eval` command is the following:

----
# oscap xccdf eval --profile PROFILE_ID --results-arf ARF_FILE --report REPORT_FILE SOURCE_DATA_STREAM_FILE
----

Where:

* `PROFILE_ID` is the ID of an XCCDF profile
* `ARF_FILE` is the file path where the results in SCAP results data stream
format (ARF) will be generated
* `REPORT_FILE` is the file path where a report in HTML format will be generated
* `SOURCE_DATA_STREAM_FILE` is the file path of the evaluated SCAP source data
stream

For example, to evaluate the `xccdf_org.ssgproject.content_profile_ospp` profile
from the `/usr/share/xml/scap/ssg/content/ssg-rhel8-ds.xml` SCAP source
data stream run this command:

----
# oscap xccdf eval --profile xccdf_org.ssgproject.content_profile_ospp --results-arf results.xml --report report.html /usr/share/xml/scap/ssg/content/ssg-rhel8-ds.xml
----

The progress and results will be shown in the terminal. Full results are
generated in `results.xml` as an SCAP result data stream. Detailed results can
be found in the HTML report `report.html`.

----
$ firefox report.html
----

TIP: Instead of the complete profile ID you can provide only a suffix of the
profile ID. For example, instead of `--profile
xccdf_org.ssgproject.content_profile_ospp` you can use just `--profile ospp`.

=== Selecting SCAP source data stream components

To evaluate a specific XCCDF benchmark that is part of a specific SCAP source
data stream, use the following command:

----
$ oscap xccdf eval --datastream-id DS_ID --xccdf-id CREF --results-arf ARF_FILE SOURCE_DATA_STREAM_FILE
----

Where:

* `DS_ID` is the ID of `<ds:data-stream>` element to be evaluated
* `XCCDF_ID` is ID of the `<ds:component-ref>` element pointing to the
desired XCCDF document
* `ARF_FILE` is a file containing the scan results in a form of an SCAP
result data stream
* `SOURCE_DATA_STREAM_FILE` is the SCAP source data stream file

NOTE: If you omit `--datastream-id` on the command line, the first data
stream from the collection will be used. If you omit `--xccdf-id`, the
first component from the checklists element will be used. If you omit
both, the first data stream that has a component in the checklists
element will be used - the first component in its checklists element
will be used.

To evaluate a specific XCCDF benchmark that is part of an SCAP source data
stream use the following options:

----
$ oscap xccdf eval --benchmark-id BENCHMARK_ID --results-arf ARF_XML SOURCE_DATA_STREAM_FILE
----

Where:

* `SOURCE_DATA_STREAM_FILE` is a file representing the SCAP source data stream
* `BENCHMARK_ID` is the value of the "id" attribute of `<xccdf:Benchmark>` 
containing component
* `ARF_FILE` is a file containing the scan results in a form of an SCAP
result data stream


=== Evaluating Standalone OVAL Definitions

The SCAP document can have a form of a single OVAL file (an OVAL Definition
file). The `oscap` tool processes the OVAL Definition file during evaluation of
OVAL definitions. It collects system information, evaluates it and generates an
OVAL Result file. The result of evaluation of each OVAL definition is printed to
standard output stream. The following examples describe the most common
scenarios involving an OVAL Definition file.

To evaluate OVAL definitions within the given OVAL Definition file the
`oscap oval eval` command can be used. Its basic form is the following:

----
$ oscap oval eval --results RESULTS_FILE OVAL_FILE
----

Where:

* `OVAL_FILE` is the OVAL Definition file
* `RESULTS_FILE` is the path where OVAL Results file will be stored

It's possible to select and evaluate one particular definition
within the given OVAL Definition file using `--id` option:

----
$ oscap oval eval --id oval:rhel:def:1000 --results oval-results.xml oval.xml
----

Where the OVAL definition being evaluated has ID `oval:rhel:def:1000`,
`oval.xml` is the OVAL Definition file and `oval-results.xml` is the
OVAL Result file.

To evaluate all definitions from the OVAL component that are part of a
particular data stream component within a SCAP source data stream, run the
following command:

----
$ oscap oval eval --datastream-id ds.xml --oval-id xccdf.xml --results oval-results.xml scap-ds.xml
----

Where `ds.xml` is the ID of a specific data stream, `xccdf.xml` is an XCCDF file
specifying the OVAL component, `oval-results.xml` is the OVAL Result file, and
`scap-ds.xml` is the SCAP source data stream collection.

When the SCAP content is represented by multiple XML files, the OVAL
Definition file can be distributed along with the XCCDF file. In such a
situation, OVAL Definitions may depend on variables that are exported
from the XCCDF file during the scan, and separate evaluation of the OVAL
definition(s) would produce misleading results. Therefore, any external
variables has to be exported to a special file that is used during the
OVAL definitions evaluation. The following commands are examples of this
scenario:

----
$ oscap xccdf export-oval-variables \
--profile united_states_government_configuration_baseline \
usgcb-rhel5desktop-xccdf.xml
----

----
$ oscap oval eval \
--variables usgcb-rhel5desktop-oval.xml-0.variables-0.xml \
--results usgcb-results-oval.xml
usgcb-rhel5desktop-oval.xml
----
Where *united_states_government_configuration_baseline* represents a
profile in the XCCDF document, *usgcb-rhel5desktop-xccdf.xml* is a file
specifying the XCCDF document, *usgcb-rhel5desktop-oval.xml* is the OVAL
Definition file, *usgcb-rhel5desktop-oval.xml-0.variables-0.xml* is the
file containing exported variables from the XCCDF file, and
*usgcb-results-oval.xml* is the the OVAL Result file.

An OVAL directives file can be used to control whether results should be "thin" or "full".
This file can be loaded by OpenSCAP using *--directives <file>* option.

Example of an OVAL directive file which enables thin results instead of
full results:

----
<?xml version="1.0" encoding="UTF-8"?>
<oval_directives
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns:oval="http://oval.mitre.org/XMLSchema/oval-common-5"
  xmlns:oval-res="http://oval.mitre.org/XMLSchema/oval-results-5"
  xmlns="http://oval.mitre.org/XMLSchema/oval-directives-5"
  xsi:schemaLocation="http://oval.mitre.org/XMLSchema/oval-results-5
    oval-results-schema.xsd http://oval.mitre.org/XMLSchema/oval-common-5
    oval-common-schema.xsd http://oval.mitre.org/XMLSchema/oval-directives-5
    oval-directives-schema.xsd">
  <generator>
    <oval:product_name>OpenSCAP</oval:product_name>
    <!-- make sure the OVAL version matches your input -->
    <oval:schema_version>5.8</oval:schema_version>
    <oval:timestamp>2017-02-04T00:00:00</oval:timestamp>
  </generator>
  <directives include_source_definitions="true">
    <oval-res:definition_true reported="true" content="thin"/>
    <oval-res:definition_false reported="true" content="thin"/>
    <oval-res:definition_unknown reported="true" content="thin"/>
    <oval-res:definition_error reported="true" content="thin"/>
    <oval-res:definition_not_evaluated reported="true" content="thin"/>
    <oval-res:definition_not_applicable reported="true" content="thin"/>
  </directives>
</oval_directives>
----

If your use-case requires thin OVAL results you most likely also want
to omit system characteristics. You can use the `--without-syschar`
option to that effect.

Usage of OVAL directives file when scanning a plain OVAL file:

----
$ oscap oval eval --directives directives.xml --without-syschar --results oval-results.xml oval.xml
----

Usage of OVAL directives file when scanning OVAL component from a source data stream:

----
$ oscap oval eval --directives directives.xml --without-syschar --datastream-id ds.xml --oval-id oval.xml --results oval-results.xml scap-ds.xml
----

It is not always clear which OVAL file will be used when multiple files
are distributed. In case you are evaluating an XCCDF file you can use:

----
$ oscap info ssg-rhel7-xccdf.xml
Document type: XCCDF Checklist
Checklist version: 1.1
Imported: 2017-01-20T14:20:43
Status: draft
Generated: 2017-01-19
Resolved: true
Profiles:
        standard
        pci-dss
        C2S
        rht-ccp
        common
        stig-rhel7-workstation-upstream
        stig-rhel7-server-gui-upstream
        stig-rhel7-server-upstream
        stig-rhevh-upstream
        ospp-rhel7-server
        nist-cl-il-al
        cjis-rhel7-server
        docker-host
        nist-800-171-cui
Referenced check files:
        ssg-rhel7-oval.xml
                system: http://oval.mitre.org/XMLSchema/oval-definitions-5
        ssg-rhel7-ocil.xml
                system: http://scap.nist.gov/schema/ocil/2
        https://www.redhat.com/security/data/oval/com.redhat.rhsa-RHEL7.xml.bz2
                system: http://oval.mitre.org/XMLSchema/oval-definitions-5
----

In the output you can see all referenced check files. In this case we see
that `ssg-rhel7-oval.xml` is referenced. To see contents of this file you
can open it in a text editor.

You can use `oscap info` with source data stream files as well. Source
data stream will often reference OVAL files that are bundled in it.
It is also possible to extract OVAL files from source data stream using
`oscap ds sds-split`.

----
$ oscap ds sds-split ssg-rhel7-ds.xml extracted/
$ ls -1 extracted/
scap_org.open-scap_cref_output--ssg-rhel7-cpe-dictionary.xml
scap_org.open-scap_cref_ssg-rhel7-xccdf-1.2.xml
ssg-rhel7-cpe-oval.xml
ssg-rhel7-ocil.xml
ssg-rhel7-oval.xml
----

After splitting the source data stream you can inspect OVAL and XCCDF files
individually using a text editor. Keep in mind that this is only an example and
file names depend on contents of the source data stream you are splitting and
that you can also inspect XCCDF and OVAL content directly in a source data
stream or a result data stream.


=== Evaluating XCCDF

When evaluating an XCCDF benchmark, `oscap` usually processes an XCCDF
file, an OVAL file and the CPE dictionary. It performs system
analysis and produces XCCDF results based on this analysis. The results
of the scan do not have to be saved in a separate file but can be
attached to the XCCDF file. The evaluation result of each XCCDF rule
within an XCCDF checklist is printed to standard output stream. The CVE
and CCE identifiers associated with the rules are printed as well. The
following is a sample output for a single XCCDF rule:

----
Title   Verify permissions on 'group' file
Rule    usgcb-rhel5desktop-rule-2.2.3.1.j
Ident   CCE-3967-7
Result  pass
----

The meaning of results is defined by https://csrc.nist.gov/CSRC/media/Publications/nistir/7275/rev-4/final/documents/nistir-7275r4_updated-march-2012_clean.pdf[XCCDF Specification].
This table lists the possible results of a single rule:

.XCCDF results
|===
|Result |Description |Example Situation

|pass
|The target system or system component satisfied all the conditions of the rule.
|

|fail
|The target system or system component did not satisfy all the conditions of the rule.
|

|error
|The checking engine could not complete the evaluation, therefore the status of the target’s compliance with the rule is not certain.
|OpenSCAP was run with insufficient privileges and could not gather all of the necessary information.

|unknown
|The testing tool encountered some problem and the result is unknown.
|OpenSCAP was unable to interpret the output of the checking engine (the output has no meaning to OpenSCAP).

|notapplicable
|The rule was not applicable to the target of the test.
|The rule might have been specific to a different version of the target OS, or it might have been a test against a platform feature that was not installed.

|notchecked
|The rule was not evaluated by the checking engine. This status is designed for rules that have no <xccdf:check> elements or that correspond to an unsupported checking system. It may also correspond to a status returned by a checking engine if the checking engine does not support the indicated check code.
|The rule does not reference any OVAL check.

|notselected
|The rule was not selected in the benchmark. OpenSCAP does not display rules that were not selected.
|The rule exists in the benchmark, but is not a part of selected profile.

|informational
|The rule was checked, but the output from the checking engine is simply information for auditors or administrators; it is not a compliance category. This status value is designed for rules whose main purpose is to extract information from the target rather than test the target.
|

|fixed
|The rule had initially evaluated to "fail", but was then fixed by automated remediation and therefore it now evaluates as "pass".
|
|===

The CPE dictionary is used to determine whether the content is
applicable on the target platform or not. Any content that is not
applicable will result in each relevant XCCDF rule being evaluated to
"notapplicable".

The following examples show the most common scenarios of XCCDF benchmark
evaluation:

* To evaluate a specific profile in an XCCDF file run this command:

----
$ oscap xccdf eval --profile Desktop --results xccdf-results.xml --cpe cpe-dictionary.xml scap-xccdf.xml
----

Where `scap-xccdf.xml` is the XCCDF document, `Desktop` is the selected
profile from the XCCDF document, `xccdf-results.xml` is a file storing
the scan results, and `cpe-dictionary.xml` is the CPE dictionary.

* You can additionally add `--rule` option to the above command to evaluate
a specific rule:

----
$ oscap xccdf eval --profile Desktop --rule ensure_gpgcheck_globally_activated  --results xccdf-results.xml --cpe cpe-dictionary.xml scap-xccdf.xml
----

Where `ensure_gpgcheck_globally_activated` is the only rule from the `Desktop`
profile which will be evaluated.

The `--rule` option can be used multiple times to evaluate multiple rules at once.

* You can skip some rules by using the `--skip-rule` option.

In the examples above we are generating XCCDF result files using the `--results`
command-line argument. You can use `--results-arf` to generate an SCAP result
data stream (also called ARF - Asset Reporting Format) XML instead.

----
$ oscap xccdf eval --benchmark-id benchmark_id --results-arf arf-results.xml scap-ds.xml
----

=== Generating results compatible with STIG Viewer

DISA STIG Viewer is a graphical user interface (GUI) application that enables
easy viewing of SCAP-formatted Security Technical Implementation Guides
(STIGs). For more information on DISA STIG Viewer see the
https://public.cyber.mil/stigs/srg-stig-tools/[SRG / STIG Tools] website.

OpenSCAP can generate results compatible with STIG Viewer even when evaluating
SCAP content that uses different rule IDs than the official DISA STIG format,
for example, content from the `scap-security-guide` package or third-party
content.

To produce results compatible with STIG Viewer, each rule in an SCAP source data
stream must contain a reference to a STIG Rule ID, and the value of the `href`
attribute must be either
`http://iase.disa.mil/stigs/Pages/stig-viewing-guidance.aspx` or
`https://public.cyber.mil/stigs/srg-stig-tools/`.

For example:
----
<Rule id="rpm_verify_permissions">
  ...
  <reference href="https://public.cyber.mil/stigs/srg-stig-tools/">SV-86473r2_rule</reference>
  ...
</Rule>
----

In the following example, we use the
`/usr/share/xml/scap/ssg/content/ssg-rhel7-ds.xml` file provided by the
`scap-security-guide` RPM package. This data stream file meets both
prerequisites for rules.

1) Scan your system using the `oscap` command with the `--stig-viewer` option.

----
$ oscap xccdf eval --profile xccdf_org.ssgproject.content_profile_stig --stig-viewer results-stig.xml /usr/share/xml/scap/ssg/content/ssg-rhel7-ds.xml
----

2) Download a STIG file of your choice, for example, from the
https://public.cyber.mil/stigs/downloads/[STIGs Document Library], and extract
it. The version of the STIG must conform to the version of the
`xccdf_org.ssgproject.content_profile_stig` profile.

3) In STIG Viewer, click on `File` and then on `Import STIG`. Then, select the
STIG in `STIGs` panel on the left side. Click on `Checklists` and then on
`Create Checklists - Check Marked STIG(s)`.

4) Import the OpenSCAP scan results by clicking on `Import` and then on `XCCDF
Results File`. Locate the `results-stig.xml` file obtained in step 1. STIG
Viewer shows the results subsequently.

NOTE: The `--stig-viewer` option serves for evaluating an SCAP source data stream
other than a STIG provided by DISA, for example, `scap-security-guide` content
and loading the generated file in STIG Viewer into a checklist created from a
STIG by DISA. When evaluating a STIG provided by DISA using `oscap`, use the
`--results` option instead. Similarly, when creating checklists based on
`scap-security-guide` content in STIG Viewer and evaluating
`scap-security-guide` by oscap, use `--results` instead of `--stig-viewer`.


== Remediating system

OpenSCAP allows one to automatically remediate systems that have been found in a
non-compliant state. For system remediation the rules in SCAP content need to
have a remediation script attached. For example, the SCAP source data streams in
the `scap-security-guide` package contain rules with remediation fix scripts.

System remediation consists of the following steps:

 . The `oscap` command performs a regular XCCDF evaluation.
 . An assessment of the results is performed by evaluating the OVAL definitions.
 Each rule that has failed is marked as a candidate for remediation.
 . The `oscap` program searches for an appropriate `<xccdf:fix>` element,
 resolves it, prepares the environment, and executes the fix script.
 . Any output of the fix script is captured by `oscap` and stored within the
 `<xccdf:rule-result>` element. The return value of the fix script is stored as
 well.
 . Whenever `oscap` executes a fix script, it immediately evaluates the OVAL
 definition again (to verify that the fix script has been applied correctly).
 During this second run, if the OVAL evaluation returns success, the result of
 the rule is *fixed*, otherwise it is an *error*.
 . Detailed results of the remediation are stored in an output XCCDF file. It
 contains two `<xccdf:TestResult>` elements. The first `<xccdf:TestResult>`
 element represents the scan prior to the remediation. The second
 `<xccdf:TestResult>` is derived from the first one and contains remediation
 results.

There are three modes of operation of `oscap` with regard to remediation:
online, offline, and review.

=== Remediation during scanning

The remediation scripts can be executed at the time of scanning. Evaluation and
remediation are performed as a part of a single command.

To enable remediation during scanning, use the `oscap xccdf eval` command with
the `--remediate` command-line option.

In this example we will execute remediation during evaluation of the OSPP profile:

----
# oscap xccdf eval --remediate --profile xccdf_org.ssgproject.content_profile_ospp --results-arf results.xml /usr/share/xml/scap/ssg/content/ssg-rhel8-ds.xml
----

The output of this command consists of two sections. The first section shows the
result of the scan prior to the remediation, and the second section shows the
result of the scan after applying the remediation. The second part can contain
only *fixed* and *error* results. The *fixed* result indicates that the scan performed
after the remediation passed. The *error* result indicates that even after
applying the remediation, the evaluation still does not pass.

=== Remediation after scanning

This feature allows you to postpone fix execution. 

In first step, the system is only evaluated, and the results are stored in the
`<xccdf:TestResult>` element in an XCCDF results file.

In the second step, `oscap` executes the fix scripts and verifies the result. It
is safe to store the results into the input file, no data will be lost. During
offline remediation, a new `<xccdf:TestResult>` element is created that is based
on the input one and inherits all the data. The newly created
`<xccdf:TestResult>` differs only in the `<xccdf:rule-result>` elements that
have failed. For those, remediation is executed.


For example:
----
# oscap xccdf eval --profile xccdf_org.ssgproject.content_profile_ospp --results results.xml /usr/share/xml/scap/ssg/content/ssg-rhel8-ds.xml
----

----
# oscap xccdf remediate --results remediation-results.xml results.xml
----

=== Reviewing remediations

The review mode allows users to store remediation instructions to a file for
further review. The remediation content is not executed during this operation.
To generate remediation instructions in the form of a shell script, run:

. Run a scan and generate XCCDF results file using the `--results` option.
+
----
# oscap xccdf eval --profile xccdf_org.ssgproject.content_profile_ospp --results results.xml /usr/share/xml/scap/ssg/content/ssg-rhel8-ds.xml
----
+
. Obtain the results ID.
+
----
$ oscap info results.xml
----
+
. Generate the fix based on the scan results.
+
----
# oscap xccdf generate fix --fix-type bash --output my-remediation-script.sh --result-id xccdf_org.open-scap_testresult_xccdf_org.ssgproject.content_profile_ospp results.xml 
----


== Tailoring

This section describes tailoring of content using a tailoring file.
Tailoring allows you to change behavior of SCAP content without its direct modification.

=== Creating Tailoring files

Tailoring files can be easily created using {workbench_url}[SCAP Workbench] which is a GUI application.

On the command line, tailoring files can be created using the `autotailor` tool.
This tool is a part of the `openscap-utils` package.

The basic syntax is:

----
$ autotailor \
--select RULE_ID --unselect RULE_ID --var-value VAR=VALUE \
--output TAILORING_FILE --new_profile_id NEW_PROFILE_ID
DS_FILENAME BASE_PROFILE_ID
----

Where:

* `--select RULE_ID` adds a rule with `RULE_ID`. This argument can be
added multiple times if needed.
* `--unselect RULE_ID` adds a rule with `RULE_ID`. This argument can be
added multiple times if needed.
* `--var-value VAR=VALUE` specifies modification of the XCCDF value in the 
form `<varname>=<value>`
* `TAILORING_FILE` is a path to the file that will be created 
* `NEW_PROFILE_ID` is the ID of the customized profile
* `DS_FILENAME` is the path to SCAP source data stream that is tailored
* `BASE_PROFILE_ID` is the original profile that we want to customize

The script creates a new file with a new profile with ID in a form `BASE_PROFILE_ID_customized`.

In the following example, we will create a customized profile with ID `custom` based on the OSPP profile from the SCAP Security Guide for Red Hat Enterprise Linux 8 (located in `/usr/share/xml/scap/ssg/content/ssg-rhel8-ds.xml` which is provided by the `scap-security-guide` RPM package) which will remove the rule `service_usbguard_enabled` and save it as a XCCDF Tailoring file into `/tmp/tailoring.xml`.

----
$ autotailor --unselect service_usbguard_enabled --output /tmp/tailoring.xml \
--new-profile-id custom /usr/share/xml/scap/ssg/content/ssg-rhel8-ds.xml ospp
----

For more details about other options of the `autotailor` program please read the `autotailor(8)` man page or run `autotailor --help`.


=== Using Tailoring files

. List profiles in the tailoring file
+
----
$ oscap info ssg-rhel8-ds-tailoring.xml
Document type: XCCDF Tailoring
Imported: 2016-08-31T11:08:16
Benchmark Hint: /usr/share/xml/scap/ssg/content/ssg-rhel8-ds.xml
Profiles:
	xccdf_org.ssgproject.content_profile_C2S_customized
----
+
. Run a scan. The command evaluates tailored data stream by
`ssg-rhel8-ds-tailoring.xml` tailoring file. XCCDF results can be found in
`results.xml` file.
+
----
$ oscap xccdf eval \
--profile xccdf_org.ssgproject.content_profile_C2S_customized \
--tailoring-file ssg-rhel8-ds-tailoring.xml \
--results results.xml
/usr/share/xml/scap/ssg/content/ssg-rhel8-ds.xml
----

WARNING: Use the ID of the customized profile (from the tailoring file), do not
use the ID of the original profile.


Instead of external tailoring file, you can also use tailoring component
integrated to data stream.

----
$ oscap info simple-ds.xml

Document type: Source Data Stream
Imported: 2016-02-02T14:06:14

Stream: scap_org.open-scap_datastream_from_xccdf_simple-xccdf.xml
Generated: (null)
Version: 1.2
Checklists:
	Ref-Id: scap_org.open-scap_cref_simple-xccdf.xml
		Status: incomplete
		Resolved: false
		Profiles:
			xccdf_org.open-scap_profile_override
		Referenced check files:
			simple-oval.xml
				system: http://oval.mitre.org/XMLSchema/oval-definitions-5
	Ref-Id: scap_org.open-scap_cref_simple-tailoring.xml
		Benchmark Hint: (null)
		Profiles:
			xccdf_org.open-scap_profile_default
			xccdf_org.open-scap_profile_unselecting
			xccdf_org.open-scap_profile_override
Checks:
	Ref-Id: scap_org.open-scap_cref_simple-oval.xml
No dictionaries.
----

To choose tailoring component `scap_org.open-scap_cref_simple-tailoring.xml`,
the command below can be used.

----
$ oscap xccdf eval \
--tailoring-id scap_org.open-scap_cref_simple-tailoring.xml \
--profile xccdf_org.open-scap_profile_default \
--results results.xml simple-ds.xml
----

The command above evaluates content using tailoring component
`scap_org.open-scap_cref_simple-tailoring.xml` from source data stream. Scan
results are stored in `results.xml` file.


== Scanning with Script Check Engine (SCE)

The Script Check Engine (SCE) is an alternative check engine for XCCDF checklist
evaluation.  SCE allows you to call shell scripts out of the XCCDF document.
This approach might be suitable for various use cases, mostly when OVAL checks
are not required. More information about SCE usage is available on this page:
{sce_web}[Using SCE].

WARNING: SCE is not part of any SCAP specification.


== Validating SCAP Content

The `oscap` tool can be used to validate the security content
against standard SCAP XML schemas. The validation results are printed to the
standard error stream (stderr). The general syntax of the validation command
is the following:

----
$ oscap module validate [module_options_and_arguments] FILE
----

where `FILE` is the full path to the file being validated. As a `module` you
can use:

  * xccdf,
  * oval,
  * cpe or
  * cve.

The only exception is the data stream module (ds), which uses the sds-validate
operation instead of validate. So for example, it would be like:

----
$ oscap ds sds-validate scap-ds.xml
----

NOTE: Note that all SCAP components within the given data stream are validated
automatically and none of the components is specified separately.

There is an extra Schematron-based validation enabled when you validate OVAL or
XCCDF specification. This validation method is slower but it provides deeper analysis.

Run one of the following commands to validate an OVAL or XCCDF document without
Schematron checks:

----
$ oscap xccdf validate --skip-schematron xccdf-file.xml
----

----
$ oscap oval validate --skip-schematron oval-file.xml
----

The results of validation are printed to standard error stream (stderr).

NOTE: Please note that for the rest of `oscap` functionality, unless you specify
--skip-validation (--skip-valid), validation will automatically occur before
files are used. Therefore, you do not need to explicitly validate a data stream
before use. Though it will not include the Schematron-based validation step.

=== Validating digital signature in SCAP source data stream

When evaluating a digitally signed SCAP source data stream OpenSCAP validates
the digital signature of the data stream. The signature validation is performed
automatically while loading the file. Data streams with invalid signatures would
be rejected and would not be evaluated. OpenSCAP uses
https://www.aleksey.com/xmlsec/[XML Security Library] with OpenSSL backend to
validate the digital signature.

The signature validation only checks that the datastream hasn't been altered
since its latest signature. OpenSCAP doesn't address trustworthiness of
certificates or public keys that are part of the `KeyInfo` signature element and
that are used to verify the signature. You should verify those keys yourself to
prevent evaluation of datastreams that have been modified and signed by bad
actors.

The signature validation can be skipped by adding the
`--skip-signature-validation` option to the `oscap xccdf eval` command.

Also, signature validation can be enforced (effectively rendering all unsigned
data streams invalid) with the `--enforce-signature` option to the `oscap xccdf eval` command.

== Generating reports, guides and scripts

Another useful features of `oscap` is the ability to generate documents in a
human-readable HTML format. This feature is used to generate security guides and
checklists, which serve as a source of information, as well as guidance for
secure system configuration. The results of system scans can also be transformed
to well-readable result reports. Moreover, remediation scripts and Ansible
playbooks can be generated if the SCAP content contains these data.

The general command syntax is the following:

----
oscap module generate sub-module [specific_module/sub-module_options_and_arguments] file
----

Where module is either `xccdf` or `oval`, `sub-module` is a type of
the generated document, and file represents an XCCDF or OVAL file. A sub-module
can be either `report`, `guide`, `custom` or `fix`. Please see
 `man oscap` for more details.


=== Generating HTML guides

To generate a HTML guide from an SCAP source data stream or an XCCDF file use the `oscap xccdf generate guide` command.

Generating a guide with profile checklist (see an
https://static.open-scap.org/examples/guide-checklist.html[example]):

----
$ oscap xccdf generate guide --profile xccdf_org.ssgproject.content_profile_ospp /usr/share/xml/scap/ssg/content/ssg-rhel8-ds.xml > guide.html
----

=== Generating HTML reports

To generate HTML scan reports after scan from the scan results in ARF or XCCDF
format the `oscap xccdf generate report` command can be used.

Generating the HTML report with information about checks (see an
https://static.open-scap.org/examples/report-xccdf-oval.html[example]):

----
$ oscap xccdf generate report arf.xml > report.html
----

TIP: The HTML report can be generated also during scan by adding the `--report`
option to the `oscap xccdf eval` command.

=== Generating bash scripts

To generate a bash remediation script from an XCCDF profile, use the `oscap
xccdf generate fix` command. OpenSCAP will extract remediation scripts for all
rules in the given profile to a file.

For example, to generate a bash remediation script for RHEL 8 OSPP profile, run:

----
$ oscap xccdf generate fix --profile ospp /usr/share/xml/scap/ssg/content/ssg-rhel8-ds.xml > fix.sh
----

The output contains fixes for all rules in the given profile including those
rules that would pass. It's because system isn't scanned during this command. If
you want to generate remediation only for the failed rules based on scan
results, refer to <<_reviewing_remediations,Reviewing remediations>>.

=== Generating Ansible Playbooks

Similar to generating bash scripts, OpenSCAP is able to extract Ansible tasks
associated with XCCDF rules and generate an Ansible Playbook that can be used to
configure the operating system according to the given profile. To generate
Anisble Playbook use the `oscap xccdf generate fix` command with `--fix-type
ansible` option.

For example, to generate Ansible Playbook from RHEL 8 OSPP profile, run:

----
$ oscap xccdf generate fix --profile ospp --fix-type ansible /usr/share/xml/scap/ssg/content/ssg-rhel8-ds.xml > playbook.yml
----

The generated Ansible Playbook is generated from an OpenSCAP profile without
preliminary evaluation. It attempts to fix every selected rule, even if the
system is already compliant. The output contains fixes for all rules in the
given profile including those rules that would pass. It's because system isn't
scanned during this command. If you want to generate remediation only for the
failed rules based on scan results, refer to <<_reviewing_remediations,Reviewing
remediations>>.

=== Generating Image Builder Blueprints

OpenSCAP can also create a remediation in form of Image Builder (OSBuild) Blueprint. This remeditaion
is intendeded to be used as a bootstrap for image creation and usually it will contain only essential
elements of the configuration, elements that would be hard or impossible to change after the image
is created, like partitioning or set of installed packages.

It is recommended to combine this type of remediation with other types, executed on the running system.

For example, to generate a blueprint remediation for RHEL 8 OSPP profile, run:

----
$ oscap xccdf generate fix --profile ospp --fix-type blueprint /usr/share/xml/scap/ssg/content/ssg-rhel8-ds.xml > blueprint.toml
----

== Details on SCAP conformance

=== Check Engines

Most XCCDF content uses the OVAL check engine. This is when OVAL
Definitions are being evaluated in order to assess a system. Complete
information of an evaluation is recorded in OVAL Results files, as
defined by the OVAL specification. By examining these files it's
possible check what definitions were used for the evaluation and why the
results are as they are. Please note these files are not generated
unless `--oval-results` is used.

Some content may use alternative check engines, for example the
{sce_web}[SCE] check engine.

Results of rules with a check that requires a check engine not supported
by OpenSCAP will be reported as *notchecked*. Check contents are not
read or interpreted in any way unless the check system is known and
supported. Following is an evaluation output of an XCCDF with unknown
check system:

----
$ oscap xccdf eval sds-datastream.xml

Title   Check group file contents
Rule    xccdf_org.example_rule_system_authcontent-group
Result  notchecked

Title   Check password file contents
Rule    xccdf_org.example_rule_system_authcontent-passwd
Result  notchecked

Title   Check shadow file contents
Rule    xccdf_org.example_rule_system_authcontent-shadow
Result  notchecked

...
----

NOTE: The *notchecked* result is also reported for rules that have no
check implemented. *notchecked* means that there was no check in that
particular rule that could be evaluated.


=== CVE, CCE, CPE and other identifiers

Each XCCDF Rule can have `<xccdf:ident>` elements inside. These elements
allow the content creator to reference various external identifiers like
CVE, CCE, CPE and others.

When scanning, `oscap` outputs identifiers of scanned rules regardless of
their results. For example:

----
Title   Ensure Repodata Signature Checking is Not Disabled For Any Repos
Rule    rule-2.1.2.3.6.a
Result  pass

Title   Verify user who owns 'shadow' file
Rule    rule-2.2.3.1.a
Ident   CCE-3918-0
Result  pass

Title   Verify group who owns 'shadow' file
Rule    rule-2.2.3.1.b
Ident   CCE-3988-3
Result  pass
----

All identifiers (if any) are printed to stdout for each rule. Since
standard output doesn't allow for compact identifier metadata to be
displayed, only the identifiers themselves are displayed there.

Identifiers are also part of the HTML report output. If the identifier
is a CVE you can click it to display its metadata from the official NVD
database (requires internet connection). OpenSCAP doesn't provide
metadata for other types of identifiers.

Another place where these identifiers can be found are machine-readable SCAP
result data stream (ARF) files. This file can be generated during the scan by
adding `--results-arf` option.

----
$ oscap xccdf eval \
--profile xccdf_org.ssgproject.content_profile_common \
--fetch-remote-resources --results-arf results.xml \
/usr/share/xml/scap/ssg/content/ssg-rhel6-ds.xml
----

Result data stream file `results.xml` contains these identifiers in `<xccdf:rule-result>`
elements.

----
<rule-result
  idref="xccdf_org.ssgproject.content_rule_partition_for_tmp"
  time="2017-01-20T14:30:18" severity="low" weight="1.000000">
  <result>pass</result>
  <ident system="https://nvd.nist.gov/cce/index.cfm">CCE-27173-4</ident>
  <check system="http://oval.mitre.org/XMLSchema/oval-definitions-5">
    <check-content-ref name="oval:ssg-partition_for_tmp:def:1" href="#oval0"/>
  </check>
</rule-result>
----

Since OpenSCAP 1.2.9 you can use the Group-By feature of HTML report
to get an overview of results based on their identifiers and references.

The HTML report can also be used to look-up Rules by their identifiers.
You can type the identifier (e.g.: CCE-27173-4) in the search box in
the HTML report and only rules with this identifier will be shown.
This can be used for any type of XCCDF identifier or reference.
You can also click on the rule title to show more details and see all
its identifiers, including the identifier you looked for.
This relies heavily on SCAP content quality, if the identifiers are
not present in the source content they will not be available in the
HTML report.

If you want to map two identifiers -- e.g.: map CCE identifier to
NIST 800-53 identifier -- you need to look-up the CCE ID in the
HTML report through the search box using the first identifier. And then,
by grouping by NIST SP 800-53 ID, you can see all NIST 800-53 IDs
related to the searched CCE ID.


=== Bundled CCE data

OpenSCAP does not provide any static or product bundled CCE data. Thus
it has no way of displaying the last generated, updated and officially
published dates of static or product bundled CCE data because the dates
are not defined.


=== CPE applicability

XCCDF rules in the content may target only specific platforms and hold
no meaning on other platforms. Such an XCCDF rule contains an
`<xccdf:platform>`` element in its body. This element references a CPE
name or CPE2 platform (defined using `<cpe2:platform-specification>`)
that could be defined in a CPE dictionary file or a CPE language file
or it can also be embedded directly in the XCCDF document.

An XCCDF rule can contain multiple `<xccdf:platform>` elements. It is
deemed applicable if at least one of the listed platforms is applicable.
If an XCCDF rule contains no `<xccdf:platform>` elements it is considered
always applicable.

If the CPE name or CPE2 platform is defined in an external file, use the
 `--cpe` option and `oscap` auto-detects format of the file. The following
command is an example of the XCCDF content evaluation using CPE name
from an external file:

----
$ oscap xccdf eval --results xccdf-results.xml --cpe external-cpe-file.xml xccdf-file.xml
----

Where `xccdf-file.xml` is the XCCDF document, `xccdf-results.xml` is a file
containing the scan results, and `external-cpe-file.xml` is the CPE
dictionary or a language file.

If you are evaluating a source data stream, `oscap` automatically
registers all CPEs contained within the data stream. No extra steps have
to be taken. You can also register an additional external CPE file, as
shown by the command below:

----
$ oscap xccdf eval --datastream-id ds.xml --xccdf-id xccdf.xml --results xccdf-results.xml --cpe additional-external-cpe.xml scap-ds.xml
----

Where `scap-ds.xml` is a file representing the SCAP data stream
collection, `ds.xml` is the particular data stream, `xccdf.xml` is the
XCCDF document, `xccdf-results.xml` is a file containing the scan
results, and `additional-external-cpe.xml` is the additional CPE
dictionary or language file.

The `oscap` tool will use an OVAL file attached to the CPE dictionary to
determine applicability of any CPE name in the dictionary.

Apart from the instructions above, no extra steps have to be taken for
content using `<cpe:fact-ref>` or `<cpe2:fact-ref>`. See the following
sections for details on resolving.

==== xccdf:platform applicability resolution

When a CPE name or language model platform is referenced via
`<xccdf:platform>` elements, resolution happens in the following order:

 . Look into embedded CPE2 language model if name is found and applicable deem
 it applicable
 . If not found or not applicable, look into external CPE2 language models
 (order of registration)
 . If not found or not applicable, look into embedded CPE dictionary
 . If not found or not applicable, look into external CPE dictionaries (order of
 registration)

If the CPE name is not found in any of the sources, it is deemed not
applicable. If it is found in any of the sources but not applicable, we
look for it elsewhere.

==== cpe:fact-ref and cpe2:fact-ref resolution

CPE name referenced from within `fact-ref` is resolved in the following
order:

.  Look into embedded CPE dictionary, if name is found and applicable
deem it applicable
.  If not found or not applicable, look into external CPE dictionaries
(order of registration)

==== Built-in CPE Naming Dictionary

Apart from the external CPE Dictionaries, `oscap` comes with an inbuilt
CPE Dictionary. The built-in CPE Dictionary contains only a few products
(sub-set of http://nvd.nist.gov/cpe.cfm[Official CPE Dictionary]) and it
is used as a fall-back option when there is no other CPE source found.

The list of inbuilt CPE names can be found in the output of

----
$ oscap --version
----

The built-in CPE dictionary will be deprecated in OpenSCAP 1.4.0.

=== Notes on the Concept of Multiple OVAL Values

This section describes advanced concepts of OVAL Variables and their
implementation in `oscap`. The SCAP specification allows for an OVAL
variable to have multiple values during a single assessment run. There
are two variable modes which can be combined:

* Multival -- A variable is assigned with multiple values at the same
time. As an example, consider a variable which refers to preferred
permission of a given file, that may take multiple values like: '600',
'400'. The evaluation tries to match each (or all) and then outputs a
single OVAL Definition result.
* Multiset -- A variable is assigned with a different value (or
multival) for different evaluations. This is known as a
*variable_instance*. As an example consider an OVAL definition which
checks that a package given by a variable is not installed. For the first
evaluation of the definition, the variable can be assigned with
'telnet-server' value, for second time the variable can be assigned with
'tftp-server' value. Therefore both evaluations may output different
results. Thus, the OVAL Results file may contain multiple results for
the same definition, these are distinguished by *variable_instance*
attribute.

These two concepts are a source of confusion for both the content
authors and the result consumers. On one hand, the first concept is well
supported by the standard and the OVAL Variable file format. It allows
multiple *<value>* elements for each *<variable>* element. On the other
hand, the second concept is not supported by an OVAL Variable schema
which prevents fully automated evaluation of the multisets (unless you
use XCCDF to bridge that gap).

TIP: `oscap` supports both variable modes as described below.

==== Sources of Variable Values

First we need to understand how a single value can be bound to a
variable in the OVAL checking engine. There are three ways to do this:

1)  OVAL Variables File -- The values of external variables can be
defined in an external file. Such a file is called an OVAL Variable File
and can be recognized by using the following command: `oscap info
file.xml`. The OVAL Variables file can be passed to the evaluation by
 `--variables` argument such as:
 
----
$ oscap oval eval \
--variables usgcb-rhel5desktop-oval.xml-0.variables-0.xml \
--results usgcb-results-oval.xml \
usgcb-rhel5desktop-oval.xml
----

2)  XCCDF Bindings -- The values of external variables can be given from
an XCCDF file. In the XCCDF file within each `<xccdf:check>` element,
there might be `<xccdf:check-export>` elements. These elements allow
transition of `<xccdf:value>` elements to `<oval:variables>` elements. The
following command allows users to export variable bindings from XCCDF to
an OVAL Variables file:

----
$ oscap xccdf export-oval-variables --profile united_states_government_configuration_baseline usgcb-rhel5desktop-xccdf.xml
----

3)  Values within an OVAL Definition File -- Variables' values defined
directly in the OVAL definitions file `<constant_variable>` and
`<local_variable>` elements.

==== Evaluation of Multiple OVAL Values

With `oscap`, there are two possible ways how two or more values can be
specified for a variable used by one OVAL definition. The approach you choose
depends on what mode you want to use, multival or multiset.

The `oscap` handles multiple OVAL values seamlessly. Users don't need to do
anything differently than for a normal scan.
The command below demonstrates evaluation of an SCAP source data stream, which
may include multiset, multival, or both concepts combined, or none of them.

----
$ oscap xccdf eval --profile my_baseline --results-arf scap-arf.xml --cpe additional-external-cpe.xml scap-ds.xml
----

==== Multival

Multival can pass multiple values to a single OVAL definition
evaluation. This can be accomplished by all three ways as described in
previous section.

1)  OVAL Variables file -- This option is straight forward. The file
format (XSD schema) allows for multiple `<value>` elements within each
`<variable>` element.

----
<variable id="oval:com.example.www:var:1" datatype="string" comment="Unknown">
  <value>600</value>
  <value>400</value>
</variable>
----

2)  XCCDF Bindings -- Use multiple `<xccdf:check-export>` referring to the
very same OVAL variable binding with multiple different XCCDF values.

----
<check system="http://oval.mitre.org/XMLSchema/oval-definitions-5">
  <check-export value-id="xccdf_com.example.www_value_1"
    export-name="oval:com.example.www:var:1"/>
  <check-export value-id="xccdf_com.example.www_value_2"
    export-name="oval:com.example.www:var:1"/>
  <check-content-ref href="my-test-oval.xml" name="oval:com.example.www:def:1"/>
</check>
----

3)  Values within OVAL Definitions file -- This is similar to using a
Variables file, there are multiple `<value>` elements allowed within
`<constant_variable>` or `<local_variable>` elements.

==== Multiset

Multiset allows for the very same OVAL definition to be evaluated
multiple times using different values assigned to the variables for each
evaluation. In OpenSCAP, this is only possible by option (2) XCCDF
Bindings. The following XCCDF snippet evaluates twice the very same OVAL
Definition, each time it binds a different value to the OVAL variable.

----
<Rule id="xccdf_moc.elpmaxe.www_rule_1" selected="true">
  <check system="http://oval.mitre.org/XMLSchema/oval-definitions-5">
    <check-export value-id="xccdf_moc.elpmaxe.www_value_1" export-name="oval:com.example.www:var:1"/>
    <check-content-ref href="my-test-oval.xml" name="oval:com.example.www:def:1"/>
  </check>
</Rule>
<Rule id="xccdf_moc.elpmaxe.www_rule_2" selected="true">
  <check system="http://oval.mitre.org/XMLSchema/oval-definitions-5">
    <check-export value-id="xccdf_moc.elpmaxe.www_value_2" export-name="oval:com.example.www:var:1"/>
    <check-content-ref href="my-test-oval.xml" name="oval:com.example.www:def:1"/>
  </check>
</Rule>
----

After the evaluation, the OVAL results file will contain multiple
result-definitions and multiple result-tests and multiple
collected-objects. The elements of the same id will be differentiated by
the value of the *variable_instance* attribute. Each of the
definitions/tests/object might have a different result of evaluation.
The following snippet of OVAL results file illustrates output of a
multiset evaluation.

----
<tests>
  <test test_id="oval:com.example.www:tst:1" version="1"
    check="at least one" result="true" variable_instance="1">
    <tested_item item_id="1117551" result="true"/>
    <tested_variable variable_id="oval:com.example.www:var:1">600</tested_variable>
  </test>
  <test test_id="oval:com.example.www:tst:1" version="1"
    check="at least one" result="false" variable_instance="2">
    <tested_item item_id="1117551" result="false"/>
    <tested_variable variable_id="oval:com.example.www:var:1">400</tested_variable>
  </test>
</tests>
----


=== Evaluating XCCDF rules with multiple checks

Normally, each XCCDF rule references to a single check with a specified name.
However, if `@name` attribute of `xccdf:check-content-ref` of a given rule is omitted,
multiple checks can be executed to evaluate the rule.
This is common for `security_patches_up_to_date` check.
By default, only a single result is produced for an XCCDF rule in such case, and the
result is computed from all results of checks in the referenced location.
In case user wants to see separate results for each check (one `xccdf:check-result` element
in results document for each check evaluated), then `multi-check` attribute
of `xccdf:check` element must be set to *true*.

----
<Rule
  id="xccdf_org.nist-testsuite.content_rule_security_patches_up_to_date"
  selected="false" weight="10.0">
  <title xml:lang="en-US">Security Patches Up-To-Date</title>
  <description xml:lang="en-US">All known security patches have been installed.</description>
  <requires idref="xccdf_org.nist-testsuite.content_group_CM-6"/>
  <requires idref="xccdf_org.nist-testsuite.content_group_SI-2"/>
  <check system="http://oval.mitre.org/XMLSchema/oval-definitions-5" multi-check="true">
    <check-content-ref href="r1100-scap11-win_rhel-patches.xml"/>
  </check>
</Rule>
----

In XCCDF specification older than 1.2, the `multi-check` element is not defined,
which means that only a single result is always produced.
To produce separate results for each check from the content older than XCCDF version 1.2,
you need to convert it first into XCCDF 1.2 using the following command:

----
$ xsltproc --stringparam reverse_DNS com.example.www /usr/share/openscap/xsl/xccdf_1.1_to_1.2.xsl xccdf.xml > xccdf-1.2.xml
----

And then patch the content using a text editor, adding `multi-check` as
shown in the example Rule snippet above.

To create a source data stream from the patched content, the following command can be used:

----
$ oscap ds sds-compose xccdf-1.2.xml source_ds.xml
----

If the original XCCDF file referenced a custom CPE dictionary, you also have to inject
the CPE dictionary into the source data stream in order to create a valid source data stream.
To add a CPE dictionary component into your data stream in place, use this command:

----
$ oscap ds sds-add cpe_dictionary.xml source_ds.xml
----

Now the `source_ds.xml` data stream can be evaluated as usual.

=== Identifying SWID tags

OpenSCAP identifies SWID tags using OVAL inventory class definitions that are
part of an SCAP source data stream or a standalone OVAL Definition file.

It supports the following 3 methods of SWID tags detection:

1. One or more `cpe2-dict:check` elements that reference an OVAL inventory
class definition that searches for the presence of a matching SWID tag.
2. A `cpe:check-fact-ref` element that references an OVAL inventory class
definition that searches for the presence of a matching SWID tag.
3. An OVAL definition that references another OVAL inventory class definition
using the `oval-def:extend_definition` element where the extended definition
searches for the presence of a matching SWID tag.

The `oscap` command handles the SWID tag detection transparently. The detection
algorithm is using OVAL's `xmlfilecontent` test. The OVAL inventory class definitions can be
evaluated in a standard way, i.e. by using the `oscap oval eval` for a
standalone OVAL Definition file or `oscap xccdf eval` for definitions that are
part of an SCAP source data stream.

For example, the following command can be used to evaluate an SCAP source data
stream that contains OVAL inventory class definitions that search for the
presence of a matching SWID tag (referenced XML files can be obtained from the
https://csrc.nist.gov/CSRC/media/Projects/scap-validation-program/documents/SCAP1.3ValidationTestContent_1-3.0.0.0.zip[SCAP 1.3 validation test suite]).

----
$ oscap xccdf eval --results-arf arf.xml --profile xccdf_gov.nist.validation_profile_r2850-rhel r2850-rhel-datastream.xml
----

As another example, the following command can be used to evaluate a standalone OVAL
Definition file that contains OVAL inventory class definitions that search for
the presence of a matching SWID tag:

----
$ oscap oval eval --results results.xml r2860-rhel-oval.xml
----


=== Notes on specifics of OVAL implementation

==== Excluding non-local filesystems using the recurse_file_system="local" attribute of a FileBehaviors entity

The scanner loosely follows the OVAL's idea behind this attribute to behave like
the coreutils utility *df* (`df -l`). This is the list of filesystems, that are
not considered local by the scanner:

* proc, sysfs
* afs
* ceph
* cifs
* smb3, smbfs
* sshfs
* ncpfs, ncp
* nfs, nfs4
* gfs, gfs2
* glusterfs
* gpfs
* pvfs2
* ocfs2
* lustre
* davfs


== List of accepted environment variables

* `OSCAP_CHECK_ENGINE_PLUGIN_DIR` - Defines path to a directory that contains plug-in libraries implementing additional check engines, eg. SCE.
* `OSCAP_CONTAINER_VARS` - Additional environment variables read by environmentvariable58_probe. The variables are separated by `\n`. It is used by `oscap-podman` and `oscap-docker` scripts during container scanning.
* `OSCAP_EVALUATION_TARGET` - Change value of target facts `urn:xccdf:fact:identifier` and `urn:xccdf:fact:asset:identifier:ein` in XCCDF results. Used during offline scanning to pass the name of the target system.
* `OSCAP_FULL_VALIDATION` - If set, XML schema validation will be performed in every step of SCAP content processing.
* `OSCAP_OVAL_COMMAND_OPTIONS` - Additional command line options for `oscap oval` module. The value of this environment variable is appended to the actual command line options of `oscap` command.
* `OSCAP_PCRE_EXEC_RECURSION_LIMIT` - Set recursion limit of regular expression matching using `pcre_exec` function.
* `OSCAP_PROBE_ROOT` - Path to a directory which contains mounted filesystem to be evaluated. Used for offline scanning.
* `SEXP_VALIDATE_DISABLE` - If set, `oscap` will not validate SEXP expressions during its execution.
* `SOURCE_DATE_EPOCH` - Timestamp in seconds since epoch. This timestamp will be used instead of the current time to populate `timestamp` attributes in SCAP source data streams created by `oscap ds sds-compose` sub-module. This is used for reproducible builds of data streams.
* `OSCAP_PROBE_MEMORY_USAGE_RATIO` - maximum memory usage ratio (used/total) for OpenSCAP probes, default: 0.1

Also, OpenSCAP uses `libcurl` library which also can be configured using environment variables. See https://curl.se/libcurl/c/libcurl-env.html[the list of libcurl environment variables].

== Using external or remote resources

Some SCAP content references external resources. For example SCAP Security Guide
uses external OVAL file to check that the system is up to date and has no known
security vulnerabilities. However, other content can use external resources for
other purposes.

When you are evaluating SCAP content with external resources the `oscap` tool
will warn you:

----
$ oscap xccdf eval \
--profile xccdf_org.ssgproject.content_profile_common \
/usr/share/xml/scap/ssg/content/ssg-rhel7-ds.xml

WARNING: This content points out to the remote resources. Use `--fetch-remote-resources' option to download them.
WARNING: Skipping https://www.redhat.com/security/data/oval/com.redhat.rhsa-RHEL7.xml.bz2 file which is referenced from XCCDF content
----

By default the `oscap` tool will not blindly download and execute remote content.
If you trust your local content and the remote content it references, you can use
the `--fetch-remote-resources` option to automatically download it using the
`oscap` tool.

----
$ oscap xccdf eval \
--fetch-remote-resources \
--profile xccdf_org.ssgproject.content_profile_common \
/usr/share/xml/scap/ssg/content/ssg-rhel7-ds.xml
Downloading: https://www.redhat.com/security/data/oval/com.redhat.rhsa-RHEL7.xml.bz2 ... ok
Title   Ensure /var/log Located On Separate Partition
Rule    xccdf_org.ssgproject.content_rule_partition_for_var_log
...
----

On systems that don't have a direct internet access or if the user doesn't want OpenSCAP to connect to the network it's possible to download the remote content using other tools, save it to a directory and then pass it to OpenSCAP as a file.
To do that, use `--local-files` instead of `--fetch-remote-resources` as argument of the `oscap` command.

In place of the remote data stream component OpenSCAP  will attempt to use a file whose file name is equal to `name` attribute of the `uri` element within the `catalog` element within the `component-ref` element representing a checklist in the data stream if such file exists.

In the following example, the `ssg-rhel8-ds.xml` is an SCAP source datastream.
It needs some checks from a remote component. The remote component's `component-ref` ID is `scap_org.open-scap_cref_security-data-oval-com.redhat.rhsa-RHEL8.xml`  and the `component-ref` is pointing to `https://www.redhat.com/security/data/oval/com.redhat.rhsa-RHEL8.xml`.
The checks from the remote component are used in the only checklist in the data stream.
The `component-ref` of the checklist component contains a `catalog` where one of the `uri` elements maps the remote component's `component-ref` ID in the `uri` attribute to the actual name `security-data-oval-com.redhat.rhsa-RHEL8.xml` which is the value of the `name` attribute.
Therefore, we can download the remote data from `https://www.redhat.com/security/data/oval/com.redhat.rhsa-RHEL8.xml` and save it as `security-data-oval-com.redhat.rhsa-RHEL8.xml` to some directory.
Then, we execute `oscap` with `--local-files` and provide a path to the directory where it's located.
It will pick the file and use it instead of the remote data and it won't connect to the network.

----
$ mkdir ~/scap-files
$ wget -O ~/scap-files/security-data-oval-com.redhat.rhsa-RHEL8.xml https://www.redhat.com/security/data/oval/com.redhat.rhsa-RHEL8.xml
...
$ oscap xccdf eval --local-files ~/scap-files --profile ospp ssg-rhel8-ds.xml
----

== Practical Examples
This section demonstrates practical usage of certain security content provided
for Red Hat products.

These practical examples show usage of industry standard checklists that
were validated by NIST.

=== Auditing System Settings with SCAP Security Guide
The SSG project contains guidance for settings of Red Hat Enterprise Linux 7.

1) Install the SSG

----
$ sudo yum install -y scap-security-guide
----

2) To inspect the security content use the `oscap info` module:

----
$ oscap info /usr/share/xml/scap/ssg/rhel7/ssg-rhel7-ds.xml
----

The output of this command contains available configuration profiles. To audit
your system settings choose the
 `xccdf_org.ssgproject.content_profile_rht-ccp` profile and run the
evaluation command . For example, the The following command is used to assess
the given system against a draft SCAP profile for Red Hat Certified Cloud
Providers:

----
$ oscap xccdf eval \
--profile xccdf_org.ssgproject.content_profile_rht-ccp \
--results ssg-rhel7-xccdf-result.xml \
--report ssg-rhel7-report.html \
/usr/share/xml/scap/ssg/rhel7/ssg-rhel7-ds.xml
----


=== Auditing Security Vulnerabilities of Red Hat Products
The Red Hat Security Response Team provides OVAL definitions for all
vulnerabilities (identified by CVE name) that affect Red Hat Enterprise
Linux 3, 4, 5, 6, 7 and 8. This enable users to perform a vulnerability scan
and diagnose whether system is vulnerable or not. The data is provided in
three ways -- OVAL file, OVAL + XCCDF and an SCAP source data stream.

==== OVAL + XCCDF

1)  Download the content
---------------------------------------------------------------------------------
$ wget https://www.redhat.com/security/data/metrics/com.redhat.rhsa-all.xccdf.xml
$ wget https://www.redhat.com/security/data/oval/com.redhat.rhsa-all.xml
---------------------------------------------------------------------------------

2)  Run the scan
--------------------------------------------------------------------------------------------
$ oscap xccdf eval --results results.xml --report report.html com.redhat.rhsa-all.xccdf.xml
--------------------------------------------------------------------------------------------

This is the sample output. It reports that Red Hat Security
Advisory (RHSA-2013:0911) was issued but update was not applied so a
system is affected by multiple CVEs (CVE-2013-1935, CVE-2013-1943,
CVE-2013-2017)

------------------------------------------------------------------------------------
Title   RHSA-2013:0911: kernel security, bug fix, and enhancement update (Important)
Rule    oval-com.redhat.rhsa-def-20130911
Ident   CVE-2013-1935
Ident   CVE-2013-1943
Ident   CVE-2013-2017
Result  fail
------------------------------------------------------------------------------------

Human readable report *report.html* is generated, as well as "machine"
readable report **results.xml**. Both files hold information about
vulnerability status of scanned system. They map RHSA to CVEs and report
what security advisories are not applied to the scanned system. CVE identifiers
are linked with National Vulnerability Databases where additional information
like CVE description, CVSS score, CVSS vector, etc. are stored.

==== OVAL only

1)  Download the content
---------------------------------------------------------------------------------
$ wget https://www.redhat.com/security/data/oval/com.redhat.rhsa-all.xml
---------------------------------------------------------------------------------

2)  Run the scan
--------------------------------------------------------------------------------------------
$ oscap oval eval --results results.xml --report report.html com.redhat.rhsa-all.xml
--------------------------------------------------------------------------------------------

This is the sample output. It reports that Red Hat Security
Advisory (RHSA-2013:0911) was issued but update was not applied.
Notice that the standard output is different from the XCCDF + OVAL output.

------------------------------------------------------------------------------------
Definition oval:com.redhat.rhsa:def:20130911: true
------------------------------------------------------------------------------------

As in case of XCCDF+OVAL, human readable report *report.html*, and "machine"
readable report **results.xml** are generated. Look of *report.html* is different
to the one generated when XCCDF checklist is used as a basis for the scan, the
information in it again holds information about vulnerability status of scanned
system, and mapping of RHSA to CVEs. CVE identifiers are linked with Red Hat
database where additional information like CVE description, CVSS score, CVSS
vector etc. are stored.


==== Source data stream
The Source data stream use-case is very similar to OVAL+XCCDF. The only
difference is that you don't have to download two separate files.

1)  Download the content

---------------------------------------------------------------------------------
$ wget https://www.redhat.com/security/data/metrics/ds/com.redhat.rhsa-all.ds.xml
---------------------------------------------------------------------------------

2)  Run the scan

--------------------------------------------------------------------------------------------
$ oscap xccdf eval --results results.xml --report report.html com.redhat.rhsa-all.ds.xml
--------------------------------------------------------------------------------------------


==== More Specialized Files

The files we used above cover multiple Red Hat products. If you only want to
scan one product - for example a specific version of Red Hat Enterprise Linux -
we advise to download a smaller specialized file covering just this one version.
Using a smaller file will utilize less bandwidth and make the evaluation
quicker.

For example for Red Hat Enterprise Linux 7 the plain OVAL file is located at:

----
$ wget https://www.redhat.com/security/data/oval/Red_Hat_Enterprise_Linux_7.xml
----

You can get a list of all the plain OVAL files by visiting
https://www.redhat.com/security/data/oval/v2/

The list of available data stream files is available at
https://www.redhat.com/security/data/metrics/ds/v2/


==== Disclaimer
NOTE: Note that these OVAL definitions are designed to only cover software and
updates released by Red Hat. You need to provide additional definitions in order
to detect the patch status of third-party software.

To find out more information about this project, see
https://www.redhat.com/security/data/metrics/.


=== How to Evaluate PCI-DSS on RHEL7
This section describes how to evaluate the Payment Card Industry Data Security
Standard (PCI-DSS) on Red Hat Enterprise Linux 7.

1) Install SSG which provides the PCI-DSS SCAP content

----
$ sudo yum install -y scap-security-guide
----

2) Verify that the PCI-DSS profile is present

----
$ oscap info /usr/share/xml/scap/ssg/content/ssg-rhel7-ds.xml
----

3) Evaluate the PCI-DSS content

----
$ oscap xccdf eval \
--results results.xml \
--profile xccdf_org.ssgproject.content_profile_pci-dss \
/usr/share/xml/scap/ssg/content/ssg-rhel7-ds.xml
----

4) Generate report readable in a web browser.

----
$ oscap xccdf generate report --output report.html results.xml
----

=== How to Evaluate DISA STIG

This section describes how to evaluate the Defense Information Systems Agency
(DISA) Security Technical Implementation Guide (STIG) on Red Hat Eneterprise
Linux 7.

. Download the DISA STIG content.
+
----
$ wget https://dl.dod.cyber.mil/wp-content/uploads/stigs/zip/U_RHEL_7_V3R2_STIG_SCAP_1-2_Benchmark.zip
----
+
. Unpack the content.
+
----
$ unzip U_RHEL_7_V3R2_STIG_SCAP_1-2_Benchmark.zip
----
+
. Display a list of available profiles.
+
----
$ oscap info U_RHEL_7_V3R2_STIG_SCAP_1-2_Benchmark.xml
----
+
. Evaluate your favorite profile, for example *MAC-1_Public*, and write
ARF results into the results.xml file.
+
----
# oscap xccdf eval \
--profile xccdf_mil.disa.stig_profile_MAC-1_Public \
--results-arf results.xml \
--report report.html \
U_RHEL_7_V3R2_STIG_SCAP_1-2_Benchmark.xml
----

If you are interested in DISA STIG content for other systems please refer to
https://public.cyber.mil/stigs/downloads/[DoD Cyber Exchange].

=== How to Evaluate United States Government Configuration Baseline (USGCB)
NOTE: NIST offers no official USGCB for RHEL6 as of September 2014 but you can
acquire the content from the {ssg_git}[SSG] project.

The USGCB content for represents Tier IV Checklist for Red Hat
Enterprise Linux 5 (as defined by NIST Special Publication 800-70).

WARNING: Proper evaluation of the USGCB document requires OpenSCAP version 0.9.1
or later.

After ensuring that version of OpenSCAP on your system is
sufficient, perform the following tasks:

1)  Download the USGCB content.
------------------------------------------------------------------------------
$ wget http://usgcb.nist.gov/usgcb/content/scap/USGCB-rhel5desktop-1.2.5.0.zip
------------------------------------------------------------------------------

2)  Unpack the USGCB content.
--------------------------------------
$ unzip USGCB-rhel5desktop-1.2.5.0.zip
--------------------------------------

3)  Run evaluation of the USGCB content.
----
$ oscap xccdf eval \
--profile united_states_government_configuration_baseline \
--cpe usgcb-rhel5desktop-cpe-dictionary.xml \
--oval-results \
--fetch-remote-resources \
--results results.xml \
usgcb-rhel5desktop-xccdf.xml
----

4) Generate a scan report that is readable in a web browser.
-----
$ oscap xccdf generate report --output report.html results.xml
-----

Additional reports can be generated from detailed OVAL result files.
Scanner outputs OVAL results files in the current directory, for each
OVAL file on input there is one output. In case of USGCB, there is
one OVAL file distributed along the XCCDF, another one which is
downloaded from Red Hat Repository. The latter contains CVE information
for each evaluated definition.

----
$ oscap oval generate report --output oval-report-1.html usgcb-rhel5desktop-oval.xml.result.xml
$ oscap oval generate report --output oval-report-2.html http%3A%2F%2Fwww.redhat.com%2Fsecurity%2Fdata%2Foval%2Fcom.redhat.rhsa-all.xml.result.xml
----

If you're interested in running evaluation of the USGCB on a remote machine using
a GUI please see:
https://open-scap.org/resources/documentation/evaluate-remote-machine-for-usgcb-compliance-with-scap-workbench/[Evaluate
Remote Machine for USGCB Compliance with SCAP Workbench] tutorial.


=== How to Evaluate Third-Party Guidances
The SCAP content repository hosted at {nvd}[National Vulnerability Database]
(NVD) can be searched for publicly available guidances for a given
product. For example, as per 2013/05/11 there are
http://web.nvd.nist.gov/view/ncp/repository?tier=3&product=Red+Hat+Enterprise+Linux+5[two]
Tier III checklists for Red Hat Enterprise Linux 5. Analogously, the
MITRE Corp. hosts http://oval.mitre.org/rep-data/[repository] of OVAL
content for various platforms, sorted by versions and classes.

Likewise the USGCB, any downloaded guidance can be evaluated by
OpenSCAP.

* Examplary evaluation of DoD Consensus Security Configuration Checklist
for Red Hat Enterprise Linux 5 (2.0)
----
$ wget http://nvd.nist.gov/ncp/DoD-RHEL5-desktop.zip
$ unzip DoD-RHEL5-desktop.zip
$ oscap xccdf eval \
--profile DOD_baseline_1.0.0.1 \
--cpe dcb-rhel5_cpe-dictionary.xml \
--results result.xml \
--oval-results \
dcb-rhel5_xccdf.xml
----

* Examplary evaluation of Red Hat 5 STIG Benchmark (Version 1, Release 12)
----
$ wget http://iasecontent.disa.mil/stigs/zip/July2015/U_RedHat_5_V1R12_STIG_SCAP_1-1_Benchmark.zip
$ unzip U_RedHat_5_V1R12_STIG_SCAP_1-1_Benchmark.zip
$ oscap xccdf eval \
--profile MAC-2_Public \
--cpe U_RedHat_5_V1R12_STIG_SCAP_1-1_Benchmark-cpe-dictionary.xml \
--results result.xml \
--oval-results \
U_RedHat_5_V1R12_STIG_SCAP_1-1_Benchmark-xccdf.xml
----

Furthermore, any individual file from the archive can be inspected using
the `oscap info` command line option. The oscap program does not have
the concept of importing SCAP files, therefore it can process any SCAP
files available on the filesystem. That is possible because the SCAP
standard files are native file formats of the OpenSCAP.


=== How to check that patches are up-to-date on Red Hat Enterprise Linux 6 or 7
This section describes how to check that software patches are up-to-date using
external OVAL content.

1) Install the SSG

----
$ sudo yum install -y scap-security-guide
----

2a) Evaluate common profile for RHEL 6

----
$ oscap xccdf eval \
--profile xccdf_org.ssgproject.content_profile_common \
--fetch-remote-resources \
--results-arf results.xml \
/usr/share/xml/scap/ssg/content/ssg-rhel6-ds.xml
----

2b) Evaluate common profile for RHEL 7

----
$ oscap xccdf eval \
--profile xccdf_org.ssgproject.content_profile_common \
--fetch-remote-resources \
--results-arf results.xml \
/usr/share/xml/scap/ssg/content/ssg-rhel7-ds.xml
----

This command evaluates common profile for Red Hat Enterprise Linux 6 or 7. Part of
the profile is a rule to check that patches are up-to-date. To evaluate the rule
correctly, oscap tool needs to download an up-to-date OVAL file from Red Hat servers. This can be
allowed using `--fetch-remote-resources` option. Result of this scan will be saved
in `results.xml` using ARF format.


== Scanning remote and virtual machines or containers

Apart from the `oscap` command, OpenSCAP provides also other utilities for
special purposes. Those utilities use `oscap` under the hood, but they
enable users to perform advanced tasks in a single command.
This manual gives a quick overview of and shows basic usage of these tools.
Each of the tools have its own manual page that gives more detailed information.

To install these tools install the `openscap-utils` package.

----
# dnf install openscap-utils
----

=== Scanning remote machines

The `oscap-ssh` command is a simple tool for scanning remote machines with
OpenSCAP over network and collecting results.

The tool uses SSH connection to copy the SCAP content to a remote machine, then
it runs an evaluation of the target system and downloads the results back.
The remote machine needs to have OpenSCAP installed.

The tool can evaluate source data streams and OVAL files.
Usage of the tool mimics usage and options of `oscap` tool.

In the following example, we will scan a remote Fedora server located on IP address
*192.168.1.13* that listens for SSH connections on port *22*.
The server will be scanned for compliance with the *Common Profile for General-Purpose
Fedora Systems* provided by SCAP Security Guide.
HTML report is written out as *report.html* on the local machine.

----
$ oscap-ssh root@192.168.1.13 22 xccdf eval \
--profile xccdf_org.ssgproject.content_profile_common \
--report report.html \
/usr/share/xml/scap/ssg/content/ssg-fedora-ds.xml
----

=== Scanning containers and container images using oscap-podman

The `oscap-podman` tool can be used to scan Linux containers and container images.
Usage of the tool mimics usage and options of `oscap` tool.

NOTE: `oscap-podman` is available only on Fedora and Red Hat Enterprise Linux 8
or newer. On other systems use `oscap-docker` instead.


. Get the ID of a container or a container image, for example:
+
----
# podman images
REPOSITORY                       TAG     IMAGE ID      CREATED       SIZE
registry.access.redhat.com/ubi8  latest  3269c37eae33  2 months ago  208 MB
----
+
. Evaluate the SCAP content, for example:
+
----
# oscap-podman 3269c37eae33 xccdf eval --report report.html --profile ospp /usr/share/xml/scap/ssg/content/ssg-rhel8-ds.xml 
----

Note that the `oscap-podman` command requires root privileges.

=== Scanning of Docker containers and images using oscap-docker

The `oscap-docker` is used to scan Docker containers and images. It can
assess vulnerabilities in the container or image and check their compliance
with security policies. Usage of the tool mimics usage and options
of `oscap` tool.

NOTE: `oscap-docker` isn't available on Fedora and on Red Hat Enterprise Linux 8
or newer. On other systems use `oscap-podman` instead.

The `oscap-docker` tool uses a technique called offline scanning.
That means that the filesystem of the container is mounted to a directory
on the host. The mounted filesystem is read-only. OpenSCAP then assess
the container from the host. Therefore no agent is installed
in the container and container is not touched or changed in any way.

In the first example, we will perform a vulnerability assessment
of an Docker image of Red Hat Enterprise Linux 7 (named *rhel7*). The command
will attach docker image, determine OS variant/version, download CVE stream
applicable to the given image and finally it will evaluate the image
for vulnerabilities. CVE stream is a list of vulnerabilities in SCAP format
and is downloaded directly from Red Hat.
HTML report is written out as *report.html* on the local machine.

----
$ oscap-docker image-cve rhel7 --report report.html
----

In the second example, we will check the same *rhel7* image for
compliance with a security policy specified in an XCCDF checklist.

----
$ oscap-docker image rhel7 xccdf eval --report report.html xccdf.xml
----

To scan running containers, commands are very similar, just replace
"image-cve" with "container-cve" and "image" with "container".

=== Scanning of virtual machines using oscap-vm

OpenSCAP provides a simple tool to evaluate virtual machines called `oscap-vm`.

The tool can scan given virtual machine directly from the virtualisation host.
Usage of the tool mimics usage and options of `oscap` tool.

Similarly to `oscap-docker`, this utility also uses offline scanning,
so it doesn't install anything in the guest, doesn't require OpenSCAP
installed in the guest and it doesn't create or change anything in the
guest's filesystem.

=== Scanning arbitrary filesystems using oscap-chroot

A very simple script `oscap-chroot` can be used to perform
an offline scan of a filesystem that is mounted at arbitrary path.
It can be used for scanning of custom objects that are not supported
by `oscap-docker` or `oscap-vm`, like containers in other
formats than Docker.
Again, usage of the tool mimics usage and options of `oscap` tool.

== Scanning and remediating the system at boot time

OpenSCAP can scan and remediate the system at boot time using systemd's `system-update.target`.
The `oscap-remediate.service` is expecting the `/system-update` symlink (universal trigger for all services in system-update's requires list) which points to a file with base name `oscap-remediate-offline.conf.sh`.
The file itself could be located anywhere, but it should be accessible at boot time. This configuration file is essentially a Bash script with a set of environment variables, loaded with `source` by the service.
Upon the start the service will immediately remove the symlink to prevent invocation loop but it won't touch the configuration file itself. A helper tool, `oscap-remediate-offline`, can be used to bootstrap the configuration and prime the `/system-update` symlink, but its flexibility is limited and in general it should only be used for debugging.

WARNING: The `oscap-remediate-offline` tool should not be considered as a stable API for priming the service. The *only* API of the service is the configuration file and the `/system-update` symlink pointing to it.

Configuration variables:
----
# Mandatory -----------------------------

# The path to the data stream file
OSCAP_REMEDIATE_DS=/some/data_stream.xml

# The ID of the profile to use
OSCAP_REMEDIATE_PROFILE_ID=some_profile

# Optional ------------------------------

# Data stream, XCCDF or Benchmark IDs
# Benchmark ID and DS + XCCDF IDs pair are mutually
# exclusive. DS + XCCDF IDs will take precedence
OSCAP_REMEDIATE_DATASTREAM_ID=some_ds_id
OSCAP_REMEDIATE_XCCDF_ID=some_xccdf_id
OSCAP_REMEDIATE_BENCHMARK_ID=some_bench_id

# Tailoring file and tailoring component ID
OSCAP_REMEDIATE_TAILORING=/some/tailoring.xml
OSCAP_REMEDIATE_TAILORING_ID=tailoring_id

# Where to write ARF result and HTML report
# No defaults, they won't be generated if
# they are not requested explicitly
OSCAP_REMEDIATE_ARF_RESULT=/some/arf_res.xml
OSCAP_REMEDIATE_HTML_REPORT=/some/report.html

# Log file name and verbosity
OSCAP_REMEDIATE_VERBOSE_LOG=/var/some_verbose.log
# Optional even if OSCAP_REMEDIATE_VERBOSE_LOG is provided (default: INFO)
OSCAP_REMEDIATE_VERBOSE_LEVEL=INFO
----

== Frequently Asked Questions (FAQs)
*Why do I get "notchecked" results when I use e.g. https://dl.dod.cyber.mil/wp-content/uploads/stigs/zip/U_Red_Hat_Enterprise_Linux_7_V2R3_STIG.zip[STIG checklist]?*

The downloaded guidance contains rule descriptions, but it doesn't contain OVAL checks which could be used for evaluation by OpenSCAP. You can find guidances with implemented OVAL checks and also with remediations at https://github.com/ComplianceAsCode/content[ComplianceAsCode] project, which contains wide range of profiles.

*I try to apply a tailoring file, but OpenSCAP still evaluates rules that I have unselected. How can I enforce my changes of the profile?*

Make sure that you provide the ID of the customized profile in `--profile` option instead of the ID of the original profile.
If you created the tailoring file using SCAP Workbench, you were prompted to choose the ID of the customized profile. You can display the ID of the customized profile by running `oscap info <your_tailoring_file>`. By default, the ID of the customized profile ends with `_customized` suffix.

*My SCAP source data stream contains rule `security_patches_up_to_date` which needs to download some data from the internet to work.*
*But I'm in an air gapped environment so it can't download it.*
*Can I download it separately and pass it to oscap?*

Yes, it's possible, you can download the file on other computer that is connected to the internet and then copy the file to the system where you run `oscap`.
Instead of the `--fetch-remote-resources` option you will use the `--local-files` option.
For more information, please refer to section <<_using_external_or_remote_resources,Using external or remote resources>>.
