Analyzing Computer Security: A Threat / Vulnerability / Countermeasure Approach

9. Scanning the Horizon

Chapter Spotlight

• Port scanning, vulnerability enumeration, topology mapping

• Subnets and architectural protections; security perimeter

• Firewalls: their purpose, design, and configurations

• Network address translation

Attack: Investigation, Intrusion, and Compromise 369

Threat: Port Scan 370

Attack Details 371

Harm: Knowledge and Exposure 374

Recurring Thread: Legal—Are Port Scans Legal? 375

Vulnerability: Revealing Too Much 376

Vulnerability: Allowing Internal Access 376

Countermeasure: System Architecture 377

Countermeasure: Firewall 378

Countermeasure: Network Address Translation (NAT) 397

Countermeasure: Security Perimeter 399

Conclusion 400

Exercises 402

“Keep your hands in your pockets and don’t touch ...