Internal vs. External Vulnerability Scanning: Do You Need Both?

Understanding Your Attack Surface

Your organization has multiple attack surfaces, not just what's visible from the internet. Understanding the difference between internal and external vulnerability scanning helps you protect all of them.

External Vulnerability Scanning

External scanning evaluates your internet-facing assets from an outside perspective, essentially seeing what attackers see.

What It Covers

• Public websites and web applications

• Internet-facing APIs

• Email servers (SMTP, IMAP)

• VPN gateways

• Cloud services and infrastructure

• DNS configurations

Why It Matters

• First line of defense against external attackers

• Required by most compliance frameworks

• Catches misconfigurations that expose internal systems

• Validates firewall and perimeter security

Typical Findings

• SSL/TLS misconfigurations

• Exposed admin interfaces

• Outdated software versions

• Missing security headers

• Open ports that should be closed

Internal Vulnerability Scanning

Internal scanning evaluates your network from inside the perimeter: what an attacker or malicious insider would see after gaining initial access.

What It Covers

• Workstations and laptops

• Internal servers

• Network devices (switches, routers)

• Printers and IoT devices

• Internal applications

• Active Directory infrastructure

Why It Matters

• Catches vulnerabilities missed by perimeter security

• Identifies lateral movement opportunities

• Validates internal segmentation

• Discovers shadow IT and unauthorized devices

• Required for comprehensive compliance

Typical Findings

• Missing patches on internal systems

• Weak or default credentials

• Unnecessary services running

• Insecure file shares

• Vulnerable internal applications

Do You Need Both?

Short answer: Yes.

The Assume-Breach Mindset

Modern security assumes attackers will eventually get past your perimeter through phishing, compromised credentials, or supply chain attacks. Internal scanning shows what they'd find.

Compliance Requirements

Most frameworks require both:

• PCI-DSS: Explicitly requires both internal and external scanning

• SOC 2: Risk assessment should cover internal systems

• ISO 27001: Comprehensive vulnerability management expected

Different Risk Profiles

External and internal vulnerabilities present different risks:

• External: Direct attack path, often first target

• Internal: Enables privilege escalation and lateral movement

Recommended Scanning Cadence

Getting Started

If you're only doing one type today, start with external scanning since it's your most exposed attack surface. Then add internal scanning as you mature your program.

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Need help implementing both internal and external vulnerability scanning? See our managed scanning plans.