Ubuntu 24.04/26.04 LTS Hardening & Audit Guide

The Ubuntu Long Term Support (LTS) series, including Ubuntu 24.04 LTS (Noble Numbat) and Ubuntu 26.04 LTS, represents the foundation of modern cloud and enterprise infrastructure deployments. Securing Ubuntu LTS nodes requires a combined approach of package checksum verification, cryptographic policy enforcement, SSH daemon hardening, kernel parameter sysctl tuning, and automated audit scanning via OpenSCAP and Lynis.

This guide details the Ansible System Integrity Management Platform (ASIMP) workflow for evaluating, auditing, and hardening Ubuntu 24.04 LTS and 26.04 LTS host environments.

🧭 Scope & Distribution Matrix

ASIMP provides target-aware validation for Ubuntu LTS releases, integrating package integrity checking (debsums), Security Compliance Assessment Protocol (SCAP), and Lynis hardening:

📊 Architectural Paradigm: Mode Separation

ASIMP strictly separates operations into two distinct execution modes, controlled via the execution_mode variable:

1. Mode A: Reporting Only (execution_mode: "report"):
   • Performs non-destructive compliance scanning and evaluation.
   • Outputs visual HTML reports and XML results.
   • Does not apply hardening, but may create report directories and files.
2. Mode B: Doing (execution_mode: "remediate"):
   • Performs a pre-remediation baseline assessment (“Phase 1: Measure”).
   • Applies automated package upgrades, file permission controls, SSH hardening, and kernel sysctl tuning (“Phase 2: Harden”).
   • Performs package checksum verification using debsums.
   • Executes a post-remediation evaluation scan (“Phase 3: Re-Measure”).
   • Outputs a comparative scorecard.

🚀 Ansible Playbook Execution Guide

The dedicated playbook playbooks/ubuntu_lts_hardening.yml automates both modes across Ubuntu 24.04 LTS and 26.04 LTS targets.

1. Execute Reporting Only Mode

To run a non-destructive security assessment and view compliance reports:

ansible-playbook -i inventory/hosts playbooks/ubuntu_lts_hardening.yml -e "execution_mode=report"

2. Execute Doing (Remediation & Hardening) Mode

To run baseline audits, apply Ubuntu LTS security hardening and package updates, and generate verification reports:

ansible-playbook -i inventory/hosts playbooks/ubuntu_lts_hardening.yml -e "execution_mode=remediate"

🐳 Unprivileged Sandbox & Fallback Strategy

Inside unprivileged container environments or Google Jules sandboxes (detected via /home/jules):

1. Privilege Safety Guards: Tasks modifying restricted kernel settings or system services run with ignore_errors: true or evaluate is_sandbox_jules.
2. Mock Auditing: Diagnostic scorecards gracefully report simulated baseline and hardened metrics without halting workflow execution.