Network Security Audit: Methodology and Action Plan for CIOs

Network security audit methodology: scope, frameworks (NIST, ISO 27001, MITRE ATT&CK), testing (vulnerability assessment, penetration testing, red teaming), reporting and action plan. 2026 CIO guide.

Audit types

• Configuration audit: review of settings against best practices
• Compliance audit: NIS2, ISO 27001, PCI-DSS
• Vulnerability scanning: Qualys, Tenable, Rapid7
• Penetration testing: simulation of an external or internal attacker
• Red teaming: long-term simulated adversary engagement
• TLPT (Threat-Led Penetration Testing): mandatory under DORA

Frameworks

• NIST CSF: Identify, Protect, Detect, Respond, Recover
• ISO 27001/27002: 114 controls
• CIS Critical Controls: 18 priority controls
• MITRE ATT&CK: adversary tactics and techniques
• OWASP Top 10: web applications

Audit phases

1. Scoping

• Scope (sites, IPs, applications)
• Objectives
• Constraints (working hours, availability)
• NDA and authorization

2. Reconnaissance

• External network mapping (OSINT)
• Port scanning (Nmap)
• OS and service fingerprinting
• Vulnerability discovery

3. Exploitation

• Active testing (for penetration tests and red team engagements)
• Lateral movement
• Privilege escalation
• Data exfiltration simulation

4. Reporting

• Executive summary (1-2 pages)
• Findings with CVSS scores
• Remediation priorities
• Recommendations
• Timeline

Service providers in France

• Thales Cyber
• Capgemini Cybersecurity
• Orange Cyberdefense
• Wavestone
• Synetis
• Fireeye Mandiant
• Ernst & Young Cybersecurity

Audit budget

• Vulnerability scan: €5-15k
• Internal and external penetration testing: €20-60k
• Red team engagement: €80-200k
• TLPT (DORA): €150-500k

Recommended frequency

• Vulnerability scanning: continuous (automated tools)
• Penetration testing: at least annually (required by NIS2)
• Red team engagement: every 2-3 years
• After every major change: mandatory

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