Introduction to Security Auditing

In today’s interconnected digital landscape, organizations must ensure their systems adhere to industry standards and resist ever-evolving threats. Security auditing is the systematic evaluation of a system’s security posture through examination of configurations, policies, and software components. By integrating automated tools such as Lynis and OpenSCAP, professionals can perform comprehensive audits, generate actionable reports, and maintain continuous compliance.

Lynis: The Open Source Security Auditor

Overview and Philosophy

Lynis is a versatile security auditing tool for Unix-based systems. Created by CISOfy, it performs in-depth scans of system components, identifies vulnerabilities, and provides remediation tips. Its modular architecture and plugin support make it ideal for diverse environments—from servers and containers to embedded devices.

Key Features

• Comprehensive checks: Kernel, file systems, authentication, software packages, services.
• Customizable profiles: Define scan scope and severity levels.
• Reporting: Detailed logs, HTML output, and compliance summaries.
• Plugin system: Extend functionality for specialized audits.

Installation and Setup

On Debian/Ubuntu:
apt-get install lynis
On Red Hat/CentOS:
yum install lynis

After installation, review the configuration file at /etc/lynis/lynis.prf to adjust parameters such as skip tests or report output format.

Performing an Audit

1. Run a quick scan:
   lynis audit system
2. Examine the log at /var/log/lynis.log.
3. Generate an HTML report:
   lynis show report

Interpreting Results

Hardening Index: A numerical score (0–100) indicating how well the system is configured. A higher index reflects stronger security postures.
Warnings Suggestions: Actionable advice to remediate identified issues, such as patching software or tightening file permissions.

OpenSCAP: The SCAP Framework Implementation

Understanding SCAP

SCAP (Security Content Automation Protocol) is a suite of specifications managed by NIST that standardizes how security software communicates configuration and vulnerability information. OpenSCAP is the open source reference implementation that supports scanning, compliance auditing, and vulnerability assessment.

Core Components

• oscap: Primary command line tool for scans and transformations.
• Datastreams: Collections of XCCDF (checklists), OVAL definitions, and remediation content.
• SARIF/HTML Reporting: Multiple output formats for integration with other tools.

Installation and Configuration

On RHEL/CentOS:
yum install openscap openscap-scanner
On Fedora:
dnf install openscap openscap-scanner

Obtain a SCAP content stream, e.g., the SSG CentOS 7 DataStream, and prepare it for scanning:

oscap ds sds-create --output data_stream-merged.xml ssg-centos7-ds.xml

Executing a Compliance Scan

To run an XCCDF-based audit:

oscap xccdf eval --profile pci-dss --results results.xml --report report.html data_stream-merged.xml

This command executes the PCI-DSS profile, exports raw results to results.xml, and creates an HTML summary report.html.

Customizing Policies

Modify or create new XCCDF profiles to suit organizational requirements. Use oscap xccdf subcommands to list, select, and edit rules:

• List available rules: oscap info data_stream-merged.xml
• Filter by severity or category.
• Generate tailored checklists for targeted audits.

Comparative Analysis

Integrating into DevSecOps Workflows

Embedding security audits into continuous integration/continuous deployment (CI/CD) pipelines ensures that new builds and configurations remain compliant. Consider the following best practices:

• Automate scans on code commits using Jenkins, GitLab CI, or GitHub Actions.
• Store and version-control custom profiles and remediation scripts.
• Generate machine-readable reports (SARIF/JSON) for vulnerability triaging.
• Enforce pass/fail gates based on audit severity thresholds.

Best Practices and Recommendations

1. Maintain Up-to-Date Baselines

Regularly synchronize SCAP content with the latest standards and update Lynis to receive new checks and security advisories.

2. Secure Remote Auditing

When performing audits on distributed systems, channel traffic through a secure VPN to protect credentials and sensitive data in transit. Recommended providers include
ExpressVPN,
NordVPN,
Surfshark, and
ProtonVPN.

3. Prioritize Remediations

Categorize findings by severity and impact. Address critical misconfigurations first, then allocate resources to medium and low-risk items.

4. Document and Track Progress

Use ticketing systems (e.g., Jira, Redmine) to assign remediation tasks and monitor their completion. Archive audit reports for compliance audits and forensic analysis.

5. Train Teams and Establish Ownership

Ensure system administrators, DevOps engineers, and security teams understand audit tools and results. Define clear responsibilities for maintaining compliance automations.

Conclusion

Security auditing with Lynis and OpenSCAP provides a powerful combination of flexibility and compliance rigor. By leveraging Lynis’s broad checks and OpenSCAP’s standardized frameworks, organizations can continuously monitor and fortify their systems against emerging threats. Integrating these tools into DevSecOps pipelines, safeguarding audit traffic with reputable VPN solutions, and following best practices for remediation and documentation will establish a robust, proactive security posture.