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ComplianceAsCode Developer Guide

1. Introduction

This document tries to provide information useful for ComplianceAsCode/content project contributors. We will guide you through the structure of the project. We will explain the directory layout, used formats and the build system.

2. Mailing List

3. Building ComplianceAsCode

3.1. Installing build dependencies

On Red Hat Enterprise Linux 6/7 make sure the packages cmake, openscap-utils, PyYAML, python-jinja2 and their dependencies are installed:

yum install cmake make openscap-utils PyYAML python-jinja2

On Red Hat Enterprise Linux 8 and Fedora the package list is the same but python2 packages need to be replaced with python3 ones:

yum install cmake make openscap-utils python3-pyyaml python3-jinja2

On Ubuntu and Debian, make sure the packages libopenscap8, libxml2-utils, python3-jinja2, python3-yaml, xsltproc and their dependencies are installed:

apt-get install cmake make expat libopenscap8 libxml2-utils ninja-build python3-jinja2 python3-yaml xsltproc
Important
Version 1.0.8 or later of openscap-utils is required to build the content.

(optional) Install git if you want to clone the GitHub repository to get the source code:

# Fedora/RHEL
yum install git

# Ubuntu/Debian
apt-get install git

(optional) Install the ShellCheck package to perform fix script static analysis:

# Fedora/RHEL
yum install ShellCheck

# Ubuntu/Debian
apt-get install shellcheck

(optional) Install yamllint and ansible-lint packages to perform Ansible playbooks checks. These checks are not enabled by default in CTest, to enable them add -DANSIBLE_CHECKS=ON option to cmake.

# Fedora/RHEL
yum install yamllint ansible-lint

# Ubuntu/Debian (to install ansible-lint on Debian you will probably need to
# enable Debian Backports repository)
apt-get install yamllint ansible-lint

(optional) Install the ninja build system if you want to use it instead of make for faster builds:

# Fedora/RHEL
yum install ninja-build

# Ubuntu/Debian
apt-get install ninja-build

(optional) Install the json2html package if you want to generate HTML report statistics:

pip install json2html

if you are using python3:

pip3 install json2html

3.2. Downloading the source code

Download and extract a tarball from the list of releases:

# change X.Y.Z for desired version
ssg_version="X.Y.Z"
wget "https://github.com/ComplianceAsCode/content/releases/download/v$ssg_version/scap-security-guide-$ssg_version.tar.bz2"
tar -xvjf ./scap-security-guide-$ssg_version.tar.bz2
cd ./scap-security-guide-$ssg_version/

Or clone the GitHub repository:

git clone https://github.com/ComplianceAsCode/content.git
cd content/
# (optional) select release version - change X.Y.Z for desired version
git checkout vX.Y.Z
# (optional) select latest development version
git checkout master

3.3. Building

To build all the security content:

cd build/
cmake ../
# To build all security content
make -j4
# To build security content for one specific product, for example for *Red Hat Enterprise Linux 7*
make -j4 rhel7

Or use the build_product script from base directory that removes whatever is in the build directory and builds specific product:

./build_product rhel7

(optional) To build only specific content for one specific product:

cd build/
cmake ../
make -j4 rhel7-content  # SCAP XML files for RHEL7
make -j4 rhel7-guides  # HTML guides for RHEL7
make -j4 rhel7-tables  # HTML tables for RHEL7
make -j4 rhel7-profile-bash-scripts  # remediation Bash scripts for all RHEL7 profiles
make -j4 rhel7-profile-playbooks # Ansible Playbooks for all RHEL7 profiles
make -j4 rhel7  # everything above for RHEL7

(optional) Configure options before building using a GUI tool:

cd build/
cmake-gui ../
make -j4

(optional) Use the ninja build system (requires the ninja-build package):

cd build/
cmake -G Ninja ../
ninja-build  # depending on the distribution just "ninja" may also work

(optional) Generate statistics for products and profiles. Some of the statistics generated are: implemented OVAL, bash, ansible for rules, missing CCE, etc:

cd build/
cmake ../
make -j4 stats # create statistics for all products
make -j4 profile-stats # create statistics for all profiles in all products

You can also create statistics per product, to do that just prepend the product name (e.g.: rhel7-stats) to the make target.

It is possible to generate HTML output by triggering similar command:

cd build/
cmake ../
make -j4 html-stats # create statistics for all products, as a result <product>/stats.html file is created.
make -j4 html-profile-stats # create statistics for all profiles in all products, as a result <product>/profile-stats.html file is created

If you want to go deeper into statistics, refer to Profile Statistics and Utilities section.

3.3.1. Building compliant SCAP 1.2 content

By default, the build system builds SCAP content with OVAL 5.11. This means that the SCAP 1.3 datastream conforms to SCAP standard version 1.3. But the SCAP 1.2 datastream is not fully conformant with SCAP standard version 1.2, as up to OVAL 5.10 version is allowed. As SCAP 1.3 allows up to OVAL 5.11 and SCAP 1.2 allows up to OVAL 5.10.

To build fully compliant SCAP 1.2 content:

If you use build_product script, pass --oval510 option:

./build_product --oval510 <product-name>

If you use cmake command, pass -DSSG_TARGET_OVAL_MINOR_VERSION:STRING=10:

cd build/
cmake -DSSG_TARGET_OVAL_MINOR_VERSION:STRING=10 ../
make

And use the datastream with suffix -1.2.xml.

3.4. Build outputs

When the build has completed, the output will be in the build folder. That can be any folder you choose but if you followed the examples above it will be the content/build folder.

3.4.1. SCAP XML files

The SCAP XML files will be called ssg-${PRODUCT}-${TYPE}.xml. For example ssg-rhel7-ds.xml is the SCAP 1.3 Red Hat Enterprise Linux 7 source datastream, and ssg-rhel7-ds-1.2.xml is the SCAP 1.2 source datastream.

We recommend using source datastream if you have a choice. The build system also generates separate XCCDF, OVAL, OCIL and CPE files:

$ ls -1 ssg-rhel7-*.xml
ssg-rhel7-cpe-dictionary.xml
ssg-rhel7-cpe-oval.xml
ssg-rhel7-ds.xml
ssg-rhel7-ds-1.2.xml
ssg-rhel7-ocil.xml
ssg-rhel7-oval.xml
ssg-rhel7-pcidss-xccdf-1.2.xml
ssg-rhel7-xccdf-1.2.xml
ssg-rhel7-xccdf.xml

These can be ingested by any SCAP-compatible scanning tool, to enable automated checking.

3.4.2. HTML Guides

The human readable HTML guide index files will be called ssg-${PRODUCT}-guide-index.html. For example ssg-rhel7-guide-index.html. This file will let the user browse all profiles available for that product. The prose guide HTML contains practical, actionable information for auditors and administrators. They are placed in the guides folder.

$ ls -1 guides/ssg-rhel7-*.html
guides/ssg-rhel7-guide-ospp42.html
guides/ssg-rhel7-guide-ospp.html
guides/ssg-rhel7-guide-pci-dss.html
...

3.4.3. HTML Reference Tables

Spreadsheet HTML tables - potentially useful as the basis for a Security Requirements Traceability Matrix (SRTM) document:

$ ls -1 tables/table-rhel7-*.html
...
tables/table-rhel7-nistrefs-ospp.html
tables/table-rhel7-nistrefs-stig.html
tables/table-rhel7-pcidssrefs.html
tables/table-rhel7-srgmap-flat.html
tables/table-rhel7-srgmap.html
tables/table-rhel7-stig.html
...

3.4.4. Ansible Playbooks

Profile Ansible Playbooks

These Playboks contains the remediations for a profile.

$ ls -1 ansible/rhel7-playbook-*.yml
ansible/rhel7-playbook-C2S.yml
ansible/rhel7-playbook-ospp.yml
ansible/rhel7-playbook-pci-dss.yml
...
Rule Ansible Playbooks

These Playboks contains just the remediation for a rule, in the context of a profile.

$ ls -1 ansible/rhel7-playbook-*.yml
$ ls -1 rhel7/playbooks/pci-dss/*.yml
rhel7/playbooks/pci-dss/account_disable_post_pw_expiration.yml
rhel7/playbooks/pci-dss/accounts_maximum_age_login_defs.yml
rhel7/playbooks/pci-dss/accounts_password_pam_dcredit.yml
rhel7/playbooks/pci-dss/accounts_password_pam_lcredit.yml
...

3.4.5. Profile Bash Scripts

These Bash Scripts contains the remediations for a profile.

$ ls -1 bash/rhel7-script-*.sh
bash/rhel7-script-C2S.sh
...
bash/rhel7-script-ospp.sh
bash/rhel7-script-pci-dss.sh
...

3.5. Testing

To ensure validity of built artifacts prior to installation, we recommend running our test suite against the build output. This is done with CTest:

cd content/
cd build/
cmake ../
make -j4
ctest -j4

Note: CTest does not run SSG Test Suite which provides simple system of test scenarios for testing profiles and rule remediations.

3.6. Installation

System-wide installation:

cd content/
cd build/
cmake ../
make -j4
sudo make install

(optional) Custom install location:

cd content/
cd build/
cmake ../
make -j4
sudo make DESTDIR=/opt/absolute/path/to/ssg/ install

(optional) System-wide installation using ninja:

cd content/
cd build/
cmake -G Ninja ../
ninja-build
ninja-build install

3.7. (optional) Building a tarball

To build a tarball with all the source code:

cd build/
make package_source

3.8. (optional) Building a package

To build a package for testing purposes:

cd build/
# disable any product you would not like to bundle in the package. For example:
cmake -DSSG_PRODUCT_FEDORA:BOOL=OFF../
# build the package.
make package

Currently, RPM and DEB packages are supported by this mechanism. We recommend only using it for testing. Please follow downstream workflows for production packages.

3.9. (optional) Building a ZIP file

To build a zip file with all generated source data streams and kickstarts:

cd build/
make zipfile

There is also target to build zip file containing contents specific for a vendor’s product.

cd build/
# To build content zipfiles of all vendors:
make vendor-zipfile
# To build Red Hat zipfiles:
make redhat-zipfile

3.10. Build the docker container image

Use a suitable Dockerfile present in the Dockerfiles directory and build the image. This will take care of the build environment and all necessary setup.

docker build --no-cache --file Dockerfile --tag oscap:$(date -u +%Y%m%d%H%M) --tag oscap:latest .

3.11. Build the content using the container image

To build all the content, run a container without any flags.

docker run --cap-drop=all --name scap-security-guide oscap:latest

Using docker cp to copy all the generated content to the your host:

docker cp scap-security-guide:/home/oscap/content/build $(pwd)/container_build

4. Creating Content

4.1. Directory Structure/Layout

4.1.1. Top Level Structure/Layout

Under the top level directory, there are directories and/or files for different products, shared content, documentation, READMEs, Licenses, build files/configuration, etc.

Important Top Level Directory Descriptions
Directory Description

linux_os

Contains security content for Linux operating systems. Contains rules, OVAL checks, Ansible tasks, Bash remediations, etc.

applications

Contains security content for applications such as OpenShift or OpenStack. Contains rules, OVAL checks, Ansible tasks, Bash remediations, etc.

shared

Contains templates which can generate, Jinja macros, Bash remediation functions.

tests

Contains the test suite for content validation and testing, contains also unit tests.

build

Can be used to build the content using CMake.

build-scripts

Scripts used by the build system.

cmake

Contains the CMake build configuration files.

Dockerfiles

Contains Dockerfiles to build content test suite container backends.

docs

Contains the User Guide and Developer Guide, manual page template, etc.

ssg

Contains Python ssg module which is used by most of the scripts in this repository.

utils

Miscellaneous scripts used for development but not used by the build system.

The remaining directories such as fedora, rhel7, etc. are product directories.

Important Top Level File Descriptions
File Description

CMakeLists.txt

Top-level CMake build configuration file

Contributors.md

DO NOT MANUALLY EDIT script-generated file

Contributors.xml

DO NOT MANUALLY EDIT script-generated file

DISCLAIMER

Disclaimer for usage of content

Dockerfile

CentOS7 Docker build file

LICENSE

Content license

README.md

Project README file

4.1.2. Benchmark Structure/Layout

Benchmarks are directories that contain benchmark.yml file. We have multiple benchmarks in our project:

Name

Location

Linux OS

/linux_os/guide

Applications

/applications (Notice no guide subdirectory there!)

Java Runtime Environment

/jre/guide

Fuse 6

/fuse6/guide

EAP6

/eap6/guide

Firefox

/firefox/guide

Chromium

/chromium/guide

The Linux OS benchmark describes Linux Operating System in general. This benchmark is used by multiple ComplianceAsCode products, eg. rhel7, fedora, ubuntu1404, sle11 etc. The benchmark is located in /linux_os/guide.

The products specify which benchmark they use as a source of content in their product.yml file using benchmark_root key. For example, rhel7 product specifies that it uses the Linux OS benchmark.

$ cat rhel7/product.yml
product: rhel7
full_name: Red Hat Enterprise Linux 7
type: platform

benchmark_root: "../linux_os/guide"

.....

Rules from multiple locations can be used for a single Benchmark. There is an optional key additional_content_directories for a list of paths to some arbitrary Groups of Rules to be included in the benchmark. Of all the rules collected only following would become a part of the benchmark:

  • rules that have the prodtype specified in correspondence with the benchmark;

  • rules that have no prodtype metadata.

.....

benchmark_root: "../applications"
additional_content_directories:
    - "../linux_os/guide"

.....

The Benchmarks are organized into directory structure. The directories represent either groups or rules. The group directories contain group.yml and rule directories rule.yml. The name of the group directory is the group ID, without the prefix. Similarly, the name of the rule directory if the rule ID, without the prefix.

For example, the Linux OS Benchmark is structured in this way:

.
├── benchmark.yml
├── intro
│   ├── general-principles
│   ├── group.yml
│   └── how-to-use
├── services
│   ├── apt
│   ├── avahi
│   ├── cron_and_at
│   ├── deprecated
│   ├── dhcp
│   ├── dns
│   ├── ftp
│   ├── group.yml
│   ├── http
│   ├── imap
│   ├── ldap
│   ├── mail
│   ├── nfs_and_rpc
│   .......
│   .......
└── system
    ├── accounts
    ├── auditing
    ├── bootloader-grub2
    ├── bootloader-grub-legacy
    ├── entropy
    ├── group.yml
    ├── logging
......

4.1.3. Product Structure/Layout

When creating a new product, use the guidelines below for the directory layout:

  • Do not use capital letters

  • If product versions are required, use major versions only. For example, rhel7, ubuntu16, etc.

  • If the content to be produced does not matter on versions, do not add version numbers. For example: fedora, firefox, etc.

  • In addition, use only a maxdepth of 3 directories.

  • See the README for more information about the changes needed.

Following these guidelines help with the usability and browsability of using and navigating the content.

For example:

$ tree -d rhel7
rhel7
├── cpe
├── kickstart
├── overlays
├── profiles
└── transforms

7 directories
Product Level Directory Descriptions

Directory

Description

cpe

Required Contains the Common Platform Enumeration (CPE) product identifier that is provided from NIST.

kickstart

Optional Contains product kickstart or build files to be used in testing, development, or production (not recommended) of compliance content.

overlays

Required Contains overlay files for specific standards organizations such as NIST, DISA STIG, PCI-DSS, etc.

profiles

Required Contains profiles that are created and tailored to meet government or commercial compliance standards.

transforms

Required Contains XSLT files and scripts that are used to transform the content into the expected compliance document such as XCCDF, OVAL, Datastream, etc.

Important

For any of the Required directories that may not yet add content, add a .gitkeep file for any empty directories.

5. Updating Reference and Overlay Content

5.1. Reference Content

5.1.1. STIG Reference Content

5.2. STIG Overlay Content

stig_overlay.xml maps an official product/version STIG release with a SSG product/version STIG release.

stig_overlay.xml should never be manually created or updated. It should always be generated using create-stig-overlay.py.

5.2.1. Creating stig_overlay.xml

To create stig_overlay.xml, there are two things that are required: an official non-draft STIG release from DISA containing a XCCDF file (e.g. U_Red_Hat_Enterprise_Linux_7_STIG_V1R1_Manual-xccdf.xml and an XCCDF file built by the project (e.g. ssg-rhel7-xccdf.xml)

Example using create-stig-overlay.py:

$ PYTHONPATH=`./.pyenv.sh` utils/create-stig-overlay.py --disa-xccdf=disa-stig-rhel7-v1r12-xccdf-manual.xml --ssg-xccdf=ssg-rhel7-xccdf.xml -o rhel7/overlays/stig_overlay.xml

5.2.2. Updating stig_overlay.xml

To update stig_overlay.xml, use the create-stig-overlay.py script as mentioned above. Then, submit a pull request to replace the stig_overlay.xml file that is needing to be updated. Please note that as a part of this update rules that have been removed from the official STIG will be removed here as well.

6. Tools and Utilities

To run the Python utilities (those ending in .py), you will need to have the PYTHONPATH environment variable set. This can be accomplished one of two ways: by prefixing all commands with a local variable (PYTHONPATH=/path/to/scap-security-guide), or by exporting PYTHONPATH in your shell environment. We provide a script for making this easier: .pyenv.sh. To set PYTHONPATH correctly for the current shell, simply call source .pyenv.sh. For more information on how to use this script, please see the comments at the top of the file.

6.1. Testing OVAL Content

Located in utils directory, the testoval.py script allows easy testing of oval definitions. It wraps the definition and makes up an oval file ready for scanning, very useful for testing new OVAL content or modifying existing ones.

Example usage:

$ PYTHONPATH=`./.pyenv.sh` ./utils/testoval.py install_hid.xml

Create or add an alias to the script so that you don’t have to type out the full path everytime that you would like to use the testoval.py script.

$ alias testoval='/home/_username_/scap-security-guide/utils/testoval.py'

An alternative is adding the directory where testoval.py resides to your PATH.

$ export PATH=$PATH:/home/_username_/scap-security-guide/utils/

6.2. Profile Statistics and Utilities

The profile_tool.py tool displays XCCDF profile statistics. It can show number of rules in the profile, how many of these rules have an OVAL check implemented, how many have a remediation available, shows rule IDs which are missing them and other useful information.

To use the script, first build the content, then pass the built XCCDF (not DataStream) to the script.

For example, to check which rules in RHEL8 OSPP profile are missing remediations, run this command:

$ ./build_product rhel8
$ ./build-scripts/profile_tool.py stats --missing-fixes --profile ospp --benchmark build/ssg-rhel8-xccdf.xml

Note: There is an automated job which provides latest statistics from all products and all profiles, you can view it here: Statistics

The tool also can subtract rules between YAML profiles.

For example, to subtract selected rules from a given profile based on rules selected by another profile, run this command:

$ ./build-scripts/profile_tool.py sub --profile1 rhel7/profiles/ospp.profile --profile2 rhel7/profiles/pci-dss.profile

This will result in a new YAML profile containing exclusive rules to the profile pointed by the --profile1 option.

7. Contributing with XCCDFs, OVALs and remediations

There are three main types of content in the project, they are rules, defined using the XCCDF standard, checks, usually written in OVAL format, and remediations, that can be executed on ansible, bash, anaconda installer and puppet. ComplianceAsCode also has its own templating mechanism, allowing content writers to create models and use it to generate a number of checks and remediations.

7.1. Contributing

Contributions can be made for rules, checks, remediations or even utilities. There are different sets of guidelines for each type, for this reason there is a different topic for each of them.

7.1.1. Rules

Rules are input described in YAML which mirrors the XCCDF format (an XML container). Rules are translated to become members of a Group in an XML file. All existing rules for Linux products can be found in the linux_os/guide directory. For non-Linux products (e.g., jre), this content can be found in the <product>/guide. The exact location depends on the group (or category) that a rule belongs to.

For an example of rule group, see linux_os/guide/system/software/disk_partitioning/partition_for_tmp.rule. The id of this rule is partition_for_tmp.rule; this rule belongs to the disk_partitioning group, which in turn belongs to the software group (which in turn belongs to the system group). Because this rule is in linux_os/guide, it can be shared by all Linux products.

Rules describe the desired state of the system and may contain references if they are parts of higher-level standards. All rules should reflect only a single configuration change for compliance purposes.

Structurally, a rule is a YAML file (which can contain Jinja macros) that represents a dictionary.

A rule YAML file has one implied attribute:

  • id: The primary identifier for the rule to be referenced from profiles. This is inferred from the file name and links it to checks and fixes with the same file name.

A rule itself contains these attributes:

  • title: Human-readable title of the rule.

  • rationale: Human-readable HTML description of the reason why the rule exists and why it is important from the technical point of view. For example, rationale of the partition_for_tmp rule states that:

    The <tt>/tmp</tt> partition is used as temporary storage by many programs. Placing <tt>/tmp</tt> in its own partition enables the setting of more restrictive mount options, which can help protect programs which use it.

  • description: Human-readable HTML description, which provides broader context for non-experts than the rationale. For example, description of the partition_for_tmp rule states that:

    The <tt>/var/tmp</tt> directory is a world-writable directory used for temporary file storage. Ensure it has its own partition or logical volume at installation time, or migrate it using LVM.

  • severity: Is used for metrics and tracking. It can have one of the following values: unknown, info, low, medium, or high.

    Level Description

    unknown

    Severity not defined (default)

    info

    Rule is informational only. Failing the rule doesn’t imply failure to conform to the security guidance of the benchmark.

    low

    Not a serious problem

    medium

    Fairly serious problem

    high

    Grave or critical problem

    When deciding on severity levels, it is best to follow the following guidelines: .Table Vulnerability Severity Category Code Definitions

Severity

DISA Category

Category Code Guidelines

high

CAT I

Any vulnerability, the exploitation of which will directly and immediately result in loss of Confidentiality, Availability, or Integrity.

medium

CAT II

Any vulnerability, the exploitation of which has a potential to result in loss of Confidentiality, Availability, or Integrity.

low

CAT III

Any vulnerability, the existence of which degrades measures to protect againstloss of Confidentiality, Availability, or Integrity.

+ The severity of the rule can be overridden by a profile with refine-rule selector. * platform: Defines applicability of a rule. For example, if a rule is not applicable to containers, this should be set to machine, which means it will be evaluated only if the targeted scan environment is either bare-metal or virtual machine. Also, it can restrict applicability on higher software layers. By setting to shadow-utils, the rule will have its applicability restricted to only environments which have shadow-utils package installed. The available options can be found in the file <product>/cpe/<product>-cpe-dictionary.xml (e.g.: rhel8/cpe/rhel8-cpe-dictionary.xml). In order to support a new value, an OVAL check (of inventory class) must be created under shared/checks/oval/ and referenced in the dictionary file. * ocil: Defines asserting statements to check whether or not the rule is valid. * ocil_clause: This attribute contains the statement which describes how to determine whether the statement is true or false. Check out encrypt_partitions.rule in linux_os/guide/system/software/disk_partitioning/: this contains a partitions do not have a type of crypto_LUKS value for ocil_clause. This clause is prefixed with the phrase "It is the case that".

A rule may contain those reference-type attributes:

  • identifiers: This is related to products that the rule applies to; this is a dictionary. Currently, only the Common Configuration Enumeration or CCE identifier is supported. Other identifiers can be added as well. Contributions to add these other identifiers are welcomed. The table below shows a list of common identifiers and their current support in a rule:

    URI Supported Identifier Value Description

    http://cce.mitre.org

    Yes

    Common Configuration Enumeration (CCE) – the identifier value MUST be a CCE version 5 number

    http://cpe.mitre.org

    No

    CPE –the identifier value MUST be a CPE version 2.0 or 2.3 name

    http://cve.mitre.org

    No

    CVE –the identifier value MUST be a CVE number

    http://www.cert.org

    No

    CERT Coordination Center – the identifier value SHOULD be a CERT advisory identifier (e.g., “CA-2004-02”)

    http://www.kb.cert.org

    No

    US-CERT vulnerability notes database – the identifier value SHOULD be a vulnerability note number (e.g., “709220”)

    http://www.us-cert.gov/cas/techalerts

    No

    US-CERT technical cyber security alerts –the identifier value SHOULD be a technical cyber security alert ID (e.g., “TA05-189A”)

    When the rule is related to RHEL, it should have a CCE. A CEE (e.g. cce@rhel7: 80328-8) is used as a global identifier that maps the rule to the product over the lifetime of a rule. There should only be one CCE mapped to a rule as a global identifier. Any other usage of CCE is no longer considered a best practice. CCEs are also product dependent which means that a different CCE must be used for each different product and product version. For example if cce@rhel7: 80328-8 exists in a rule, that CCE cannot be used for another product or version (e.g. rhel6), and the CCE MUST be retired with the rule. Available CCEs that can be assigned to new rules are listed in the shared/references/cce-rhel-avail.txt file.

  • references: This is related to the compliance document line items that the rule applies to. These can be attributes such as stigid, srg, nist, etc., whose keys may be modified with a product (e.g., stigid@rhel6) to restrict what products a reference identifier applies to. Depending on the type of reference (e.g. catalog, rulei, etc.) will depend on how many can be added to a single rule. In addition, certain references in a rule such as stigid only apply to a certain product and product version; they cannot be used for multiple products and versions

    Key Reference Type Mapping to Rule Example Format

    cis

    Center for Internet Security (catalog identifier)

    0-to-many, 0-to-1 is preferred

    5.2.5

    cjis

    Criminal Justice Information System (catalog identifier)

    0-to-1

    5.4.1.1

    cui

    Controlled Unclassified Information (catalog identifier)

    0-to-many, 0-to-1 is preferred

    3.1.7

    disa

    DISA Control Correlation Identifiers (catalog identifier)

    0-to-many

    18,172,1403

    srg, vmmsrg, etc.

    DISA Security Requirements Guide (catalog identifier)

    0-to-many

    SRG-OS-000003-GPOS-00004

    stigid@<product><product_version>

    DISA STIG identifier (rule identifier)

    0-to-1

    030874

    hipaa

    Health Insurance Portability and Accountability Act of 1996 (HIPAA) (catalog identifier)

    0-to-many

    164.308(a)(1)(ii)(D),164.308(a)(3)(ii)(A)

    nist

    National Institute for Standards and Technology 800-53 (catalog identifier)

    0-to-many

    AC-2(4),AC-17(7),AU-1(b)

    nist-csf

    National Institute for Standards and Technology Cybersecurity Framework (catalog identifier)

    0-to-many

    DE.AE-3,DE.AE-5,DE.CM-1

    ospp

    National Information Assurance Partnership (selected control identifier)

    0-to-1

    FMT_MOF_EXT.1

    pcidss

    Payment Card Industry Data Security Standard

    0-to-many, 0-to-1 is preferred

    Req-8.7.c

    See linux_os/guide/system/software/disk_partitioning/encrypt_partitions/rule.yml for an example of reference-type attributes as there are others that are not referenced above.

Some of existing rule definitions contain attributes that use macros. There are two implementations of macros:

  • Jinja macros, that are defined in shared/macros.jinja, and shared/macros-highlevel.jinja.

  • Legacy XSLT macros, which are defined in shared/transforms/*.xslt.

For example, the ocil attribute of service_ntpd_enabled uses the ocil_service_enabled jinja macro. Due to the need of supporting Ansible output, which also uses jinja, we had to modify control sequences, so macro operations require one more curly brace. For example, invocation of the partition macro looks like {{{ complete_ocil_entry_separate_partition(part="/tmp") }}} - there are three opening and closing curly braces instead of the two that are documented in the Jinja guide.

shared/macros.jinja contains specific low-level macros s.a. systemd_ocil_service_enabled, whereas shared/macros-highlevel.jinja contains general macros s.a. ocil_service_enabled, that decide which one of the specialized macros to call based on the actual product being used.

The macros that are likely to be used in descriptions begin by describe_, whereas macros likely to be used in OCIL entries begin with ocil_. Sometimes, a rule requires ocil and ocil_clause to be specified, and they depend on each other. Macros that begin with complete_ocil_entry_ were designed for exactly this purpose, as they make sure that OCIL and OCIL clauses are defined and consistent. Macros that begin with underscores are not meant to be used in descriptions.

To parametrize rules and remediations as well as Jinja macros, you can use product-specific variables defined in product.yml in product root directory. Moreover, you can define implied properties which are variables inferred from them. For example, you can define a condition that checks if the system uses yum or dnf as a package manager and based on that populate a variable containing correct path to the configuration file. The inferring logic is implemented in _get_implied_properties in ssg/yaml.py. Constants and mappings used in implied properties should be defined in ssg/constants.py.

Rules are unselected by default - even if the scanner reads rule definitions, they are effectively ignored during the scan or remediation. A rule may be selected by any number of profiles, so when the scanner is scanning using a profile the rule is included in, the rule is taken into account. For example, the rule identified by partition_for_tmp defined in shared/xccdf/system/software/disk_partitioning.xml is included in the RHEL7 C2S profile in rhel7/profiles/C2S.xml.

Checks are connected to rules by the oval element and the filename in which it is found. Remediations (i.e. fixes) are assigned to rules based on their basename. Therefore, the rule sshd_print_last_log has a bash fix associated as there is a bash script shared/fixes/bash/sshd_print_last_log.sh. As there is an Ansible playbook shared/fixes/ansible/sshd_print_last_log.yml, the rule has also an Ansible fix associated.

7.1.2. Rule Directories

The rule directory simplifies the structure of a rule and all of its associated content by placing it all under a common directory. The structure of a rule directory looks like the following example:

linux_os/guide/system/group/rule_id/rule.yml
linux_os/guide/system/group/rule_id/bash/ol7.sh
linux_os/guide/system/group/rule_id/bash/shared.sh
linux_os/guide/system/group/rule_id/oval/rhel7.xml
linux_os/guide/system/group/rule_id/oval/shared.xml

To be considered a rule directory, it must be a directory contained in a benchmark pointed to by some product. The directory must have a name that is the id of the rule, and must contain a file called rule.yml which is a YAML Rule description as described above. This directory can then contain the following subdirectories:

  • anaconda — for Anaconda remediation content, ending in .anaconda

  • ansible — for Ansible remediation content, ending in .yml

  • bash — for Bash remediation content, ending in .sh

  • oval — for OVAL check content, ending in .xml

  • puppet — for Puppet remediation content, ending in .pp

In each of these subdirectories, a file named shared.ext will apply to all products and be included in all builds, but {{{ product }}}.ext will only get included in the build for {{{ product }}} (e.g., rhel7.xml above will only be included in the build of the rhel7 guide content and not in the ol7 content). Note that .ext must be substituted for the correct extension for content of that type (e.g., .sh for bash content). Further, all of these directories are optional and will only be searched for content if present. Lastly, the product naming of content will not override the contents of platform or prodtype fields in the content itself (e.g., if rhel7 is not present in the rhel7.xml OVAL check platform specifier, it will be included in the build artifacts but later removed because it doesn’t match the platform).

Currently the build system supports both rule files (discussed above) and rule directories. For example content in this format, please see rules in linux_os/guide.

To interact with build directories, the ssg.rules and ssg.rule_dir_stats modules have been created, as well as three utilities:

  • utils/rule_dir_json.py — to generate a JSON tree describing the current content of all guides

  • utils/rule_dir_stats.py — for analyzing the JSON tree and finding information about specific rules, products, or summary statistics

  • utils/rule_dir_diff.py — for diffing two JSON trees (e.g., before and after a major change), using the same interface as rule_dir_stats.py.

For more information about these utilities, please see their help text.

To interact with rule.yml files and the OVALs inside a rule directory, the following utilities are provided:

utils/mod_prodtype.py

This utility modifies the prodtype field of rules. It supports several commands:

  • mod_prodtype.py <rule_id> list - list the computed and actual prodtype of the rule specified by rule_id.

  • mod_prodtype.py <rule_id> add <product> [<product> …​] - add additional products to the prodtype of the rule specified by rule_id.

  • mod_prodtype.py <rule_id> remove <product> [<product> …​] - remove products to the prodtype of the rule specified by rule_id.

  • mod_prodtype.py <rule_id> replace <replacement> [<replacement> …​] - do the specified replacement transformations. A replacement transformation is of the form match~replace where match and replace are a comma separated list of products. If all of the products in match exist in the original prodtype of the rule, they are removed and the products in replace are added.

This utility requires an up to date JSON tree created by rule_dir_json.py.

utils/mod_checks.py

This utility modifies the <affected> element of an OVAL check. It supports several commands on a given rule:

  • mod_checks.py <rule_id> list - list all OVALs, their computed products, and their actual platforms.

  • mod_checks.py <rule_id> delete <product> - delete the OVAL for the the specified product.

  • mod_checks.py <rule_id> make_shared <product> - moves the product OVAL to the shared OVAL (e.g., rhel7.xml to shared.xml).

  • mod_checks.py <rule_id> diff <product> <product> - Performs a diff between two OVALs (product can be shared to diff against the shared OVAL).

In addition, the mod_checks.py utility supports modifying the shared OVAL with the following commands:

  • mod_checks.py <rule_id> add <platform> [<platform> …​] - adds the specified platforms to the shared OVAL for the rule specified by rule_id.

  • mod_checks.py <rule_id> remove <platform> [<platform> …​] - removes the specified platforms from the shared OVAL.

  • mod_checks.py <rule_id> replace <replacement> [<replacement …​] - do the specified replacement against the platforms in the shared OVAL. See the description of replace under mod_prodtype.py for more information about the format of a replacement.

This utility requires an up to date JSON tree created by rule_dir_json.py.

utils/mod_fixes.py

This utility modifies the <affected> element of a remediation. It supports several commands on a given rule and for the specified remediation language:

  • mod_fixes.py <rule_id> <lang> list - list all fixes, their computed products, and their actual platforms.

  • mod_fixes.py <rule_id> <lang> delete <product> - delete the fix for the specified product.

  • mod_fixes.py <rule_id> <lang> make_shared <product> - moves the product fix to the shared fix (e.g., rhel7.sh to shared.sh).

  • mod_fixes.py <rule_id> <lang> diff <product> <product> - Performs a diff between two fixes (product can be shared to diff against the shared fix).

In addition, the mod_fixes.py utility supports modifying the shared fixes with the following commands:

  • mod_fixes.py <rule_id> <lang> add <platform> [<platform> …​] - adds the specified platforms to the shared fix for the rule specified by rule_id.

  • mod_fixes.py <rule_id> <lang> remove <platform> [<platform> …​] - removes the specified platforms from the shared fix.

  • mod_fixes.py <rule_id> <lang> replace <replacement> [<replacement …​] - do the specified replacement against the platforms in the shared fix. See the description of replace under mod_prodtype.py for more information about the format of a replacement.

This utility requires an up to date JSON tree created by rule_dir_json.py.

7.1.3. Checks

Checks are used to evaluate a Rule. They are written using a custom OVAL syntax and are stored as xml files inside the checks/oval directory for the desired platform. During the building process, the system will transform the checks in OVAL compliant checks.

In order to create a new check, you must create a file in the appropriate directory, and name it the same as the Rule id. This id will also be used as the OVAL id attribute. The content of the file should follow the OVAL specification with these exceptions:

  • The root tag must be <def-group>

  • If the OVAL check has to be a certain OVAL version, you can add oval_version="oval_version_number" as an attribute to the root tag. Otherwise if oval_version does not exist in <def-group>, it is assumed that the OVAL file applies to any OVAL version.

  • Don’t use the tags <definitions> <tests> <objects> <states>, instead, put the tags <definition> <*_test> <*_object> <*_state> directly inside the <def-group> tag.

  • TODO Namespaces

This is an example of a check, written using the custom OVAL syntax, that checks if the group that owns the file /etc/cron.allow is the root:

<def-group oval_version="5.11">
  <definition class="compliance" id="file_groupowner_cron_allow" version="1">
    <metadata>
      <title>Verify group who owns 'cron.allow' file</title>
      <affected family="unix">
        <platform>Red Hat Enterprise Linux 7</platform>
      </affected>
      <description>The /etc/cron.allow file should be owned by the appropriate
      group.</description>
    </metadata>
    <criteria>
      <criterion test_ref="test_groupowner_etc_cron_allow" />
    </criteria>
  </definition>
  <unix:file_test check="all" check_existence="any_exist"
  comment="Testing group ownership /etc/cron.allow" id="test_groupowner_etc_cron_allow"
  version="1">
    <unix:object object_ref="object_groupowner_cron_allow_file" />
    <unix:state state_ref="state_groupowner_cron_allow_file" />
  </unix:file_test>
  <unix:file_state id="state_groupowner_cron_allow_file" version="1">
    <unix:group_id datatype="int">0</unix:group_id>
  </unix:file_state>
  <unix:file_object comment="/etc/cron.allow"
  id="object_groupowner_cron_allow_file" version="1">
    <unix:filepath>/etc/cron.allow</unix:filepath>
  </unix:file_object>
Macros

Jinja macros for OVAL checks are located in macros-oval.jinja. These currently include the following high-level macros:

  • oval_sshd_config — check a parameter and value in the sshd configuration file

  • oval_grub_config — check a parameter and value in the grub configuration file

  • oval_check_config_file — check a parameter and value in a given configuration file

  • oval_check_ini_file — check a parameter and value in a given section of a given configuration file in "INI" format

Always consider reusing oval_check_config_file when creating new macros, it has some logic that will save you some time (e.g.: platform applicability).

They also include several low-level macros which are used to build the high level macros:

  • set of low-level macros to build the OVAL checks for line in file:

oval_line_in_file_criterion
oval_line_in_file_test
oval_line_in_file_object
oval_line_in_file_state
  • set of low-level macros to build the OVAL checks to test if a file exists:

oval_config_file_exists_criterion
oval_config_file_exists_test
oval_config_file_exists_object
Platform applicability

Platform applicability is given by the prodtype property in the rule.yml file. If you are using oval_check_config_file macro directly or indirectly, it should be enough to define prodtype. Default is all platforms. If you intend to define your own OVAL check please consider using oval_affected macro from macros.jinja.

Whenever possible, please reuse the macros and form high-level simplifications. This ensures consistent, high quality OVAL checks that we can edit in one place and reuse in many places. For more details on which parameters are accepted by the macros, please refer to the inline documentation in the macros-oval.jinja file.

7.2. Remediations

Remediations, also called fixes, are used to change the state of the machine, so that previously non-passing rules can pass. There can be multiple versions of the same remediation meant to be executed by different applications, more specifically Ansible, Bash, Anaconda and Puppet. They also have to be idempotent, meaning that they must be able to be executed multiple times without causing the fixes to accumulate. The Ansible’s language works in such a way that this behavior is built-in, however, for the other versions, the remediations must have it implemented explicitly. Remediations also carry metadata that should be present at the beginning of the files. This meta data will be converted in XCCDF tags during the building process. That is how it looks like and what it means:

# platform = multi_platform_all
# reboot = false
# strategy = restrict
# complexity = low
# disruption = low
Field Description Accepted values

platform

CPE name, CPE applicability language expression or even wildcards declaring which platforms the fix can be applied

Default CPE dictionary is packaged along with openscap. Custom CPE dictionaries can be used. Wildcards are multi_platform_[all, oval, fedora, debian, ubuntu, linux, rhel, openstack, opensuse, rhev, sle].

reboot

Whether or not a reboot is necessary after the fix

true, false

strategy

The method or approach for making the described fix. Only informative for now

unknown, configure, disable, enable, patch, policy, restrict, update

complexity

The estimated complexity or difficulty of applying the fix to the target. Only informative for now

unknown, low, medium, high

disruption

An estimate of the potential for disruption or operational degradation that the application of this fix will impose on the target. Only informative for now

unknown, low, medium, high

7.2.1. Ansible

Important
The minimum version of Ansible must be at the latest supported version. See https://access.redhat.com/support/policy/updates/ansible-engine for information on the supported Ansible versions.

Ansible remediations are either:

  • Stored as .yml files in directory ansible in the rule directory.

  • Generated from templates.

  • Generated using jinja2 macros.

They are meant to be executed by Ansible itself when requested by openscap, so they are written using Ansible’s own language with the following exceptions:

  • The remediation content must be only the tasks section of what would be a playbook.

    • Tasks can include blocks for grouping related tasks.

    • The when clause will get augmented in certain scenarios.

  • Notifications and handlers are not supported.

  • Tags are not necessary, because they are automatically generated during build of content.

Here is an example of an Ansible remediation that ensures the SELinux is enabled in grub:

# platform = multi_platform_rhel,multi_platform_fedora
# reboot = false
# strategy = restrict
# complexity = low
# disruption = low
- name: Ensure SELinux Not Disabled in /etc/default/grub
  replace:
    dest: /etc/default/grub
    regexp: selinux=0

The Ansible remediation will get included by our build system to the SCAP datastream in the fix element of respective rule.

The build system generates an Ansible Playbook from the remediation for all profiles. The generated Playbook is located in /build/<product>/playbooks/<profile_id>/<rule_id>.yml.

For each rule in the given product we also generate an Ansible Playbook regardless presence of the rule in any profile. The generated Playbook is located in /build/<product>/playbooks/all/<rule_id>.yml. The /build/<product>/playbooks/all/ directory represents the virtual (all) profile which consists of all rules in the product. Due to undefined XCCDF Value selectors in this pseudo-profile, these Playbooks use defaults of XCCDF Values when applicable.

We also build profile Playbook that contains tasks for all rules in the profile. The Playbook is generated in /build/ansible/<product>-playbook-<profile_id>.yml.

Jinja macros for Ansible content are located in /shared/macros-ansible.jinja. These currently include the following high-level macros:

  • ansible_sshd_set — set a parameter in the sshd configuration

  • ansible_etc_profile_set — ensure a command gets executed or a variable gets set in /etc/profile or /etc/profile.d

  • ansible_tmux_set — set a command in tmux configuration

They also include several low-level macros:

  • ansible_lineinfile — ensure a line is in a given file

  • ansible_stat — check the status of a path on the file system

  • ansible_find — find all files with matched content

  • ansible_only_lineinfile — ensure that no lines matching the regex are present and add the given line

  • ansible_set_config_file — for configuration files; set the given configuration value and ensure no conflicting values

  • ansible_set_config_file_dir — for configuration files and files in configuration directories; set the given configuration value and ensure no conflicting values

When msg is absent from any of the above macros, rule title will be substituted instead.

Whenever possible, please reuse the macros and form high-level simplifications. This ensures consistent, high quality remediations that we can edit in one place and reuse in many places.

7.2.2. Bash

Bash remediations are stored as shell script files in bash directory in rule directory. You can make use of any available command, but beware of too specific or complex solutions, as it may lead to a narrow range of supported platforms. There are a number of already written bash remediations functions available in shared/bash_remediation_functions/ directory, it is possible one of them is exactly what you are looking for.

Following, you can see an example of a bash remediation that sets the maximum number of days a password may be used:

# platform = Red Hat Enterprise Linux 7
. /usr/share/scap-security-guide/remediation_functions
populate var_accounts_maximum_age_login_defs

grep -q ^PASS_MAX_DAYS /etc/login.defs && \
    sed -i "s/PASS_MAX_DAYS.*/PASS_MAX_DAYS     $var_accounts_maximum_age_login_defs/g" /etc/login.defs
if [ $? -ne 0 ]; then
    echo "PASS_MAX_DAYS      $var_accounts_maximum_age_login_defs" >> /etc/login.defs
fi

When writing new bash remediations content, please follow the following guidelins:

  • Use four spaces for indentation rather than tabs.

  • You can use macros from shared/macros-bash.jinja in the remediation content. If the macro is used from a nested block, use the indent jinja2 filter assuming the 4-space indentation. Typically, you want to call the macro with the intended indentation, and as indent doesn’t indent the first line by default, you just pass the number of spaces as the only argument. See the remediation for rule ensure_fedora_gpgkey_installed for reference.

  • Prefer to use sed rather than awk.

  • Try to keep expressions simple, avoid double negations. Use compound lists with moderation and only if you understand them.

  • Test your script in the "strict mode" with set -e -o pipefail specified at the top of it. Make sure that the script doesn’t end prematurely in the strict mode.

  • Beware of constructs such as [ $x = 1 ] && echo "$x is one" as they violate the previous point. [ $x != 1 ] || echo "$x is one" is OK.

  • Use the die function defined in remediation_functions to handle exceptions, such as [ -f "$config_file" ] || die "Couldn’t find the configuration file '$config_file'".

  • Run shellcheck over your remediation script. Make sure that you fix all warnings that are applicable. If you are not sure, mention those warnings in the pull request description.

  • Use POSIX syntax in regular expressions, so prefer grep '^*something' over grep '^\s*something'.

Jinja macros that generate Bash remediations can be found in shared/macros-bash.jinja.

Available high-level Jinja macros to generate Bash remediations:

  • bash_sshd_config_set - Set SSH Daemon configuration option in /etc/ssh/sshd_config.

  • bash_auditd_config_set - Set Audit Daemon option in /etc/audit/auditd.conf.

  • bash_coredump_config_set - Set Coredump configuration in /etc/systemd/coredump.conf

  • bash_package_install - Install a package

  • bash_package_remove - Remove a package

  • bash_disable_prelink - disables prelinking

  • bash_dconf_settings - configure DConf settings for RHEL and Fedora systems

  • bash_dconf_lock - configure DConf locks for RHEL and Fedora systems

  • bash_service_command - enable or disable a service (either with systemctl or xinet.d)

  • bash_firefox_js_setting - configure a setting in a Mozilla Firefox JavaScript configuration file.

  • bash_firefox_cfg_setting - configure a setting in a Mozilla Firefox configuration file.

Available low-level Jinja macros that can be used in Bash remediations:

  • die - Function to terminate the remediation

  • set_config_file - Add an entry to a text configuration file

7.3. Templating

Writing OVAL checks, Bash, or any other content can be tedious work. For certain types of rules we provide templates. If there is a template that can be used for the new rule you only need to specify the template name and its parameters in rule.yml and the content will be generated during the build.

The templating system currently supports generating OVAL checks and Ansible, Bash, Anaconda and Puppet remediations. All templates can be found in shared/templates directory. The files are named template_<TYPE>_<NAME>, where <TYPE> should be OVAL, ANSIBLE, BASH, ANACONDA or PUPPET and <NAME> is the template name.

7.3.1. Using Templates

To use a template in rule.yml add template: key there and fill it accordingly. The general form is the following:

template:
    name: template_name
    vars:
        param_name: value # these parameters are individual for each template
        param_name@rhel7: value1
        param_name@rhel8: value2
    backends: # optional
        ansible: "off"
        bash: "on" # on is implicit value

The vars: key contains template parameters and their values which will be substituted into the template. Each template has specific parameters. To use different values of parameters based on product, append @ followed by product ID to the parameter name.

The backends: key is optional. By default, all languages supported by a given template will be generated. with given name exist will be generated. This key can be used to explicitly opt out from generating a certain type of content for the rule.

For example, to generate templated content except Bash remediation for rule "Package GCC is Installed" using package_installed template, add the following to rule.yml:

template:
    name: package_installed
    vars:
        pkgname: gcc
    backends:
        bash: "off"

7.3.2. List of available templates

accounts_password
  • Checks if PAM enforces password quality requirements. Checks the configuration in /etc/pam.d/system-auth (for RHEL 6 systems) or /etc/security/pwquality.conf (on other systems).

  • Parameters:

    • variable - PAM pam_cracklib (on RHEL 6) or pam_pwquality (on other systems) module name, eg. ucredit, ocredit

    • operation - OVAL operation, eg. less than or equal

  • Languages: OVAL

auditd_lineinfile
  • Checks configuration options of the Audit Daemon in /etc/audit/auditd.conf.

  • Parameters:

    • parameter - auditd configuration item

    • value - the value of configuration item specified by parameter

    • missing_parameter_pass - effective only in OVAL checks, if set to "true" and the parameter is not present in the configuration file the OVAL check will return true.

  • Languages: Ansible, Bash, OVAL

audit_rules_dac_modification
  • Checks Audit Discretionary Access Control rules

  • Parameters:

    • attr - value of -S argument in Audit rule, eg. chmod

  • Languages: Ansible, Bash, OVAL

audit_rules_file_deletion_events
  • Ensure auditd Collects file deletion events

  • Parameters:

    • name - value of -S argument in Audit rule, eg. unlink

  • Languages: Ansible, Bash, OVAL

audit_rules_login_events
  • Checks if there are Audit rules that record attempts to alter logon and logout events.

  • Parameters:

    • path - value of -w in the Audit rule, eg. /var/run/faillock

  • Languages: Ansible, Bash, OVAL

audit_rules_path_syscall
  • Check if there are Audit rules to record events that modify user/group information via a syscall on a specific file.

  • Parameters:

    • path - path of the protected file, eg /etc/shadow

    • pos - position of argument, eg. a2

    • syscall - name of the system call, eg. openat

  • Languages: Ansible, Bash, OVAL

audit_rules_privileged_commands
  • Ensure Auditd collects information on the use of specified privileged command.

  • Parameters:

    • path - the path of the privileged command - eg. /usr/bin/mount

  • Languages: Ansible, Bash, OVAL

audit_rules_unsuccessful_file_modification
  • Ensure there is an Audit rule to record unsuccessful attempts to access files

  • Parameters:

    • name - name of the unsuccessful system call, eg. creat

  • Languages: Ansible, Bash, OVAL

audit_rules_unsuccessful_file_modification_o_creat
  • Ensure there is an Audit rule to record unsuccessful attempts to access files when O_CREAT flag is specified.

  • Parameters:

    • syscall - name of the unsuccessful system call, eg. openat

    • pos - position of the O_CREAT argument in the syscall, as specified by -F audit rule argument, eg. a2

  • Languages: OVAL

audit_rules_unsuccessful_file_modification_o_trunc_write
  • Ensure there is an Audit rule to record unsuccessful attempts to access files when O_TRUNC_WRITE flag is specified.

  • Parameters:

    • syscall - name of the unsuccessful system call, eg. openat

    • pos - position of the O_TRUNC_WRITE argument in the syscall, as specified by -F audit rule argument, eg. a2

  • Languages: OVAL

audit_rules_unsuccessful_file_modification_rule_order
  • Ensure that Audit rules for unauthorized attempts to use a specific system call are ordered correctly.

  • Parameters:

    • syscall - name of the unsuccessful system call, eg. openat

    • pos - position of the flag parameter in the syscall, as specified by -F audit rule argument, eg. a2

  • Languages: OVAL

audit_rules_usergroup_modification
  • Check if Audit is configured to record events that modify account changes.

  • Parameters:

    • path - path that should be part of the audit rule as a value of -w argument, eg. /etc/group.

  • Languages: Ansible, Bash, OVAL

file_groupowner
  • Check group that owns the given file.

  • Parameters:

    • filepath - File path to be checked. If the file path ends with / it describes a directory.

    • missing_file_pass - If set to "true" the OVAL check will pass when file is absent. Default value is "false".

    • file_regex - Regular expression that matches file names in a directory specified by filepath. Can be set only if filepath parameter specifies a directory.

    • filegid - group ID (GID)

  • Languages: Ansible, Bash, OVAL

file_owner
  • Check user that owns the given file.

  • Parameters:

    • filepath - File path to be checked. If the file path ends with / it describes a directory.

    • missing_file_pass - If set to "true" the OVAL check will pass when file is absent. Default value is "false".

    • file_regex - Regular expression that matches file names in a directory specified by filepath. Can be set only if filepath parameter specifies a directory.

    • fileuid - user ID (UID)

  • Languages: Ansible, Bash, OVAL

file_permissions
  • Checks permissions (mode) on a given file.

  • Parameters:

    • filepath - File path to be checked. If the file path ends with / it describes a directory.

    • missing_file_pass - If set to "true" the OVAL check will pass when file is absent. Default value is "false".

    • file_regex - Regular expression that matches file names in a directory specified by filepath. Can be set only if filepath parameter specifies a directory.

    • filemode - File permissions in a hexadecimal format, eg. '0640'.

  • Languages: Ansible, Bash, OVAL

grub2_bootloader_argument
  • Checks kernel command line arguments in GRUB 2 configuration.

  • Parameters:

    • arg_name - argument name, eg. audit

    • arg_value - argument value, eg. '1'

  • Languages: Ansible, Bash, OVAL

kernel_module_disabled
  • Checks if the given Linux kernel module is disabled.

  • Parameters:

    • kernmodule - name of the Linux kernel module, eg. cramfs

  • Languages: Ansible, Bash, OVAL

mount
  • Checks that a given mount point is located on a separate partition.

  • Parameters:

    • mountpoint - path to the mount point, eg. /var/tmp

  • Languages: Anaconda, OVAL

mount_option
  • Checks if a given partition is mounted with a specific option such as "nosuid".

  • Parameters:

    • mountpoint - mount point on the filesystem eg. /dev/shm

    • mountoption - mount option, eg. nosuid

    • filesystem - filesystem in /etc/fstab, eg. tmpfs. Used only in Bash remediation.

    • type - filesystem type. Used only in Bash remediation.

    • mount_has_to_exist - Used only in Bash remediation. Specifies if the mountpoint entry has to exist in /etc/fstab before the remediation is executed. If set to yes and the mountpoint entry is not present in /etc/fstab the Bash remediation terminates. If set to no the mountpoint entry will be created in /etc/fstab.

  • Languages: Anaconda, Ansible, Bash, OVAL

mount_option_remote_filesystems
  • Checks if all remote filesystems (NFS mounts in /etc/fstab) are mounted with a specific option.

  • Parameters:

    • mountpoint - always set to remote_filesystems

    • mountoption - mount option, eg. nodev

    • filesystem - filesystem of new mount point (used when adding new entry in /etc/fstab), eg. tmpfs. Used only in Bash remediation.

    • mount_has_to_exist - Used only in Bash remediation. Specifies if the mountpoint entry has to exist in /etc/fstab before the remediation is executed. If set to yes and the mountpoint entry is not present in /etc/fstab the Bash remediation terminates. If set to no the mountpoint entry will be created in /etc/fstab.

  • Languages: Ansible, Bash, OVAL

mount_option_removable_partitions
  • Checks if all removable media mounts are mounted with a specific option.

  • Parameters:

    • mountpoint - always set to var_removable_partition. This is an XCCDF Value, defined in var_removable_partition.var

    • mountoption - mount option, eg. nodev

    • filesystem - filesystem of new mount point (used when adding new entry in /etc/fstab), eg. tmpfs. Used only in Bash remediation.

    • mount_has_to_exist - Used only in Bash remediation. Specifies if the mountpoint entry has to exist in /etc/fstab before the remediation is executed. If set to yes and the mountpoint entry is not present in /etc/fstab the Bash remediation terminates. If set to no the mountpoint entry will be created in /etc/fstab.

  • Languages: Anaconda, Ansible, Bash, OVAL

package_installed
  • Checks if a given package is installed. Optionally, it can also check whether a specific version or newer is installed.

  • Parameters:

    • pkgname - name of the RPM or DEB package, eg. tmux

    • evr - Optional parameter. It can be used to check if the package is of a specific version or newer. Provide epoch, version, release in epoch:version-release format, eg. 0:2.17-55.0.4.el7_0.3. Used only in OVAL checks. The OVAL state uses operation "greater than or equal" to compare the collected package version with the version in the OVAL state.

  • Languages: Anaconda, Ansible, Bash, OVAL, Puppet

package_removed
  • Checks if the given package is not installed.

  • Parameters:

    • pkgname - name of the RPM or DEB package, eg. tmux

  • Languages: Anaconda, Ansible, Bash, OVAL, Puppet

sebool
  • Checks values of SELinux booleans.

  • Parameters:

    • seboolid - name of SELinux boolean, eg. cron_userdomain_transition

    • sebool_bool - the value of the SELinux Boolean. Can be either "true" or "false". If this parameter is not specified, the rule will use XCCDF Value var_<seboolid>. These XCCDF Values are usually defined in the same directory where the rule.yml that describes the rule is located. The seboolid will be replaced by a SELinux boolean, for example: selinuxuser_execheap and in the profile you can use var_selinuxuser_execheap to turn on or off the SELinux boolean.

  • Languages: Ansible, Bash, OVAL

service_disabled
  • Checks if a service is disabled. Uses either systemd or SysV init based on the product configuration in product.yml.

  • Parameters:

    • servicename - name of the service.

    • packagename - name of the package that provides this service. This argument is optional. If packagename is not specified it means the name of the package is the same as the name of service.

    • daemonname - name of the daemon. This argument is optional. If daemonname is not specified it means the name of the daemon is the same as the name of service.

    • mask_service - Check if the service should be masked to prevent it from running. This argument is optional. Implicit value is "true".

  • Languages: Ansible, Bash, OVAL, Puppet

service_enabled
  • Checks if a system service is enabled. Uses either systemd or SysV init based on the product configuration in product.yml.

  • Parameters:

    • servicename - name of the service.

    • packagename - name of the package that provides this service. This argument is optional. If packagename is not specified it means the name of the package is the same as the name of service.

    • daemonname - name of the daemon. This argument is optional. If daemonname is not specified it means the name of the daemon is the same as the name of service.

  • Languages: Ansible, Bash, OVAL, Puppet

sshd_lineinfile
  • Checks SSH server configuration items in /etc/ssh/sshd_config.

  • Parameters:

    • parameter - name of the SSH configuration option, eg. KerberosAuthentication

    • value - value of the SSH configuration option specified by parameter, eg. "no".

    • missing_parameter_pass - If set to "true" the OVAL check will pass if the parameter is not present in /etc/ssh/sshd_config.

  • Languages: Ansible, Bash, OVAL

sysctl
  • Checks sysctl parameters. The OVAL definition checks both configuration and runtime settings and require both of them to be set to the desired value to return true.

  • Parameters:

    • sysctlvar - name of the sysctl value, eg. net.ipv4.conf.all.secure_redirects.

    • datatype - data type of the sysctl value, eg. int.

    • sysctlval - value of the sysctl value, eg. '1'. If this parameter is not specified, XCCDF Value is used instead.

  • Languages: Ansible, Bash, OVAL

timer_enabled
  • Checks if a SystemD timer unit is enabled.

  • Parameters:

    • timername - name of the SystemD timer unit, without the timer suffix, eg. dnf-automatic.

    • packagename - name of the RPM package which provides the SystemD timer unit. This parameter is optional, if it is not provided it is assumed that the name of the RPM package is the same as the name of the SystemD timer unit.

  • Languages: Ansible, Bash, OVAL

7.3.3. Creating Templates

The offer of currently available templates can be extended by developing a new template.

1) Create the template files, one for each type of file. Each one should be named template_<TYPE>_<NAME>. Where <TYPE> should be OVAL, ANSIBLE, BASH, ANACONDA or PUPPET and <NAME> is the what we will call the template name. Create these files in shared/templates directory.

Use the Jinja syntax we use elsewhere in the project; refer to the earlier section on Jinja macros for more information. The parameters should be named using uppercase letters, because the keys from rule.yml are converted to uppercase by the code that substitutes the parameters to the template.

Notice that OVAL should be written in shorthand format. This is an example of an OVAL template file called template_OVAL_package_installed:

<def-group>
  <definition class="compliance" id="package_{{{ PKGNAME }}}_installed"
  version="1">
    <metadata>
      <title>Package {{{ PKGNAME }}} Installed</title>
      <affected family="unix">
        <platform>multi_platform_all</platform>
      </affected>
      <description>The {{{ pkg_system|upper }}} package {{{ PKGNAME }}} should be installed.</description>
    </metadata>
    <criteria>
      <criterion comment="package {{{ PKGNAME }}} is installed"
      test_ref="test_package_{{{ PKGNAME }}}_installed" />
    </criteria>
  </definition>
{{{ oval_test_package_installed(package=PKGNAME, evr=EVR, test_id="test_package_"+PKGNAME+"_installed") }}}
</def-group>

Notice that you can use Jinja macros and Jinja filters in the template code.

And here is the Ansible template file called template_ANSIBLE_package_installed:

# platform = multi_platform_all
# reboot = false
# strategy = enable
# complexity = low
# disruption = low
- name: Ensure {{{ PKGNAME }}} is installed
  package:
    name: "{{{ PKGNAME }}}"
    state: present

2) Implement a callback function which will process the parameters before passing them to the Jinja engine. For example, this callback can provide default values, escape characters, check if parameters are correct, or any other processing of the parameters specific for the template.

The callback functions are located in ssg/templates.py.

The callback function must have the same name as the template name. This is the name that is used in rule.yml in name: key, for example package_installed.

The callback must have 2 parameters:

  • data - dictionary which contains the contents of vars: dictionary from rule.yml

  • lang - string, describes language, can be one of: "anaconda", "ansible", "bash", "oval", "puppet"

The callback function is executed for every supported language, so it can process the data differently for each language.

The function must always return the (modified) data dictionary.

The function must be always defined even if no processing of data is needed. In that situation the function just returns data parameter.

3) Decorate the callback function by the @template decorator. The decorator will register the template in the templating engine. The decorator has a single parameter which is a list of languages that the template provides. The list can contain the following values: "anaconda", "ansible", "bash", "oval", "puppet". The decorator parameter is mandatory. Insert the @template decorator on the line before the callback function definition.

For example, if the template name is package_installed and it provides Ansible template in shared/templates/template_ANSIBLE_package_installed and OVAL template in shared/templates/template_OVAL_package_installed, then there must be callback function package_installed in ssg/templates.py and the callback must be decorated by @template(["ansible", "oval")]. In this example, decorating the callback function lets the templating engine know that Ansible and OVAL should be generated if any rule uses package_installed in rule.yml.

The following example shows the callback function for the template mount_option, including the @template decorator. The example function declares that there is a template which name is mount_option and it provides Ansible, Bash and OVAL content. The code takes the data argument which is a dictionary with template parameters from rule.yml and based on lang it modifies the template parameters and returns the modified dictionary.

@template(["ansible", "bash", "oval"])
def mount_option(data, lang):
    if lang == "oval":
        data["pointid"] = re.sub(r"[-\./]", "_", data["mountpoint"]).lstrip("_")
    else:
        data["mountoption"] = re.sub(" ", ",", data["mountoption"])
    return data

7.4. Tests (ctest)

ComplianceAsCode uses ctest to orchestrate testing upstream. To run the test suite go to the build folder and execute ctest:

cd build/
ctest -j 4

Check out the various ctest options to perform specific testing, you can rerun just one test or skip all tests that match a regex. (See -R, -E and other options in the ctest man page)

Tests are added using the add_test cmake call. Each test should finish with a 0 exit-code in case everything went well and a non-zero if something failed. Output (both stdout and stderr) are collected by ctest and stored in logs or displayed. Make sure you never hard-code a path to any tool when doing testing (or anything really) in the cmake code. Always use configuration to find all the paths and then use the respective variable.

See some of the existing testing code in cmake/SSGCommon.cmake.

7.5. Contribution to infrastructure code

The ComplianceAsCode build and templating system is mostly written in Python.

7.5.1. Python

  • The common pattern is to dynamically add the shared/modules to the import path. The ssgcommon module has many useful utility functions and predefined constants. See scripts at ./build-scripts as an example of this practice.

  • Follow the PEP8 standard.

  • Try to keep most of your lines length under 80 characters. Although the 99 character limit is within PEP8 requirements, there is no reason for most lines to be that long.

8. Legacy Notice

This project has been created by renaming SCAP Security Guide Project (SSG). It was a project that provides security policies in SCAP format. Project outgrown former name SCAP Security Guide, and changed its name to imply broader scope than just SCAP. Therefore, the SCAP Security Guide has been transformed into ComplianceAsCode/content, which better describes the goal of the project.

This git repository was created by simply renaming and moving the SCAP Security Guide (SSG) repository to a different GitHub organization.

Due to this history, the repository contains mentions of SCAP Security Guide or ssg. Some of them are kept due to backwards compatibility.

For example, the output files produced by our build system still start by ssg- prefix. Various Linux distributions still ship our files in scap-security-guide package.

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