A comprehensive security audit is the cornerstone of any effective cybersecurity program. Phase 1: Asset Discovery using Nmap and network access control systems. Phase 2: Vulnerability scanning with Qualys, Nessus, or OpenVAS against CVE and CIS benchmarks. Phase 3: Penetration testing using MITRE ATT&CK to test exploitability. Phase 4: Configuration review against CIS benchmarks. Phase 5: Social engineering testing and physical security evaluation. Phase 6: Third-party risk assessment. Our guide includes specific tool recommendations, a 200+ item security audit checklist, risk prioritization using CVSS scoring, and a remediation roadmap template.