Internal vs External PCI Scans: A Complete Comparison Guide

Introduction

When it comes to PCI DSS compliance, vulnerability scanning is a critical security control that helps protect cardholder data. However, many organizations struggle to understand the differences between internal and external PCI scans, leading to confusion about which types of scans they need and when to perform them.

This comparison matters because choosing the wrong scanning approach—or worse, neglecting required scans—can result in non-compliance, security vulnerabilities, and potential data breaches. Both internal and external scans serve distinct purposes in your PCI compliance program, and understanding their differences is essential for maintaining a robust security posture.

Quick answer: Most organizations handling credit card data need both internal and external PCI scans. External scans are performed quarterly by an Approved Scanning Vendor (ASV) and focus on internet-facing systems. Internal scans are also performed quarterly (but can be done in-house) and examine systems within your network perimeter.

Overview of Each Option

External PCI Scans

External PCI scans are vulnerability assessments conducted from outside your network perimeter, simulating how an attacker on the internet would view and potentially exploit your systems. These scans must be performed by a PCI Security Standards Council (PCI SSC) Approved Scanning Vendor (ASV) and focus on all externally accessible IP addresses and domains.

Internal PCI Scans

Internal PCI scans are vulnerability assessments performed from within your network environment. These scans examine systems, devices, and applications that process, store, or transmit cardholder data, as well as systems that could impact the security of the cardholder data environment (CDE).

Key Differences at a Glance

Perspective: External scans test from outside; internal scans test from inside
Vendor requirement: External requires ASV; internal can be done in-house
Scope: External covers internet-facing assets; internal covers CDE systems
Frequency: Both required quarterly, but internal may need additional scans after changes

Detailed Comparison

Requirements Comparison

External Scan Requirements:

Must use a PCI-approved ASV
Quarterly scans mandatory for all SAQ types except A
Passing scans required for initial compliance
Four consecutive passing quarterly scans needed for ongoing compliance
Clean scan reports must show no vulnerabilities rated 4.0 or higher (CVSS)

Internal Scan Requirements:

Can be performed by qualified internal staff or third-party vendor
Required quarterly for most merchants (SAQ C, C-VT, D)
Personnel conducting scans must be independent from those managing scanned systems
Must follow documented methodology
Vulnerabilities rated “high” must be resolved

Scope Comparison

External Scan Scope:

All public-facing IP addresses
Web applications accessible from the internet
Email servers, DNS servers, and other internet services
Remote access points (VPN endpoints)
Cloud-hosted systems with public IPs

Internal Scan Scope:

All systems within the CDE
Devices that store, process, or transmit cardholder data
Security systems protecting the CDE (firewalls, IDS/IPS)
Connected systems that could impact CDE security
Internal web applications handling card data

Effort/Cost Comparison

External Scan Costs:

ASV fees typically range from $200-$2,000 annually
Minimal internal effort once IPs are identified
Remediation time varies based on findings
May require firewall rule reviews and adjustments

Internal Scan Costs:

Software/tools: $1,000-$10,000+ annually (if not outsourced)
Staff time for scanning and analysis
Training costs for personnel
Higher remediation effort due to larger scope
Can be outsourced for $2,000-$15,000+ annually

Use Case Fit

External Scans Best For:

E-commerce websites
Organizations with internet-facing payment applications
Businesses with remote access capabilities
Any merchant with public IP addresses

Internal Scans Best For:

Retail environments with POS systems
Call centers handling phone orders
Organizations with complex internal networks
Businesses storing cardholder data internally

When to Choose Each

Scenarios Requiring Only External Scans

1. SAQ A Merchants: If you fully outsource payment processing and have no access to cardholder data
2. Minimal Infrastructure: Organizations with no internal systems touching card data
3. Cloud-Only Operations: Businesses using only third-party hosted payment pages

Scenarios Requiring Both Scan Types

1. E-commerce with Backend Systems: Online stores that process orders internally
2. Retail Chains: Physical locations with centralized payment processing
3. B2B Operations: Companies storing customer card data for recurring billing
4. Healthcare/Hospitality: Organizations with multiple payment channels

Hybrid Approaches

Some organizations benefit from a blended strategy:

Continuous Monitoring: Implementing real-time vulnerability detection alongside quarterly scans
Risk-Based Frequency: Increasing scan frequency for critical systems
Automated Remediation: Using tools that can auto-patch certain vulnerabilities
Integrated Platforms: Solutions that combine internal and external scanning capabilities

Decision Framework

Questions to Ask Yourself

1. What is my SAQ type?
– SAQ A: External only (in most cases)
– SAQ A-EP: External required
– SAQ B, B-IP: External required
– SAQ C, C-VT, D: Both required

2. Do I have internet-facing systems?
– Yes: External scans definitely required
– No: Check if internal scans still apply

3. Do I store, process, or transmit cardholder data internally?
– Yes: Internal scans required
– No: May only need external scans

4. What are my technical capabilities?
– Strong security team: Consider in-house internal scanning
– Limited resources: Outsource both types

Evaluation Criteria

Consider these factors when planning your scanning program:

UK PCI

Specific PCI DSS requirements for your validation type
Contractual obligations from payment processors
Industry-specific regulations

Resource Availability

Internal security expertise
Budget constraints
Time available for remediation

Risk Profile

Transaction volume
Data retention practices
Network complexity
Previous security incidents

Decision Tree

“`
Start → Determine SAQ Type
↓
SAQ A? → External Scans Only (usually)
↓
SAQ B/C/D? → Both Scans Required
↓
Have ASV? → No → Select ASV for External
↓
Internal Resources? → No → Outsource Internal Scans
↓
Implement Quarterly Scanning Program
“`

Common Misconceptions

Myths Debunked

Myth 1: “One scan type can replace the other”
Reality: Internal and external scans test different attack vectors and both may be required for compliance.

Myth 2: “I can use any vulnerability scanner for PCI compliance”
Reality: External scans must be performed by a PCI-approved ASV. Internal scans need qualified personnel but don’t require ASV tools.

Myth 3: “Passing scans mean I’m secure”
Reality: Scans are point-in-time assessments. Security requires continuous monitoring and improvement.

Myth 4: “Cloud providers handle all scanning requirements”
Reality: While providers scan their infrastructure, you’re responsible for scanning your configured services and applications.

Clarifications

ASV Requirement: Only external scans require an ASV. Internal scans can be performed by qualified staff or any competent third party
Frequency: Both scan types are required quarterly at minimum, but significant changes trigger additional scans
Failing Scans: You must remediate high-risk vulnerabilities and rescan to achieve compliance
False Positives: Can be documented and disputed with proper evidence

FAQ

Q1: Can the same vendor perform both internal and external PCI scans?
A: Yes, many vendors offer both services. For external scans, ensure they’re a PCI-approved ASV. For internal scans, verify their qualifications and independence from your system management.

Q2: How long do PCI scans typically take to complete?
A: External scans usually complete within 2-24 hours depending on the number of IPs. Internal scans vary widely based on network size but typically take 4-48 hours for the scanning phase, plus additional time for analysis and reporting.

Q3: What happens if my scans fail?
A: Failed scans require remediation of identified vulnerabilities. For external scans, you must fix issues rated 4.0+ CVSS and rescan. For internal scans, address all “high” vulnerabilities. You have up to 30 days to remediate and achieve a passing scan.

Q4: Do I need to scan systems that don’t directly handle card data?
A: Yes, if those systems are connected to the CDE or could impact its security. This includes authentication servers, network devices, and security systems. Proper network segmentation can reduce the scope of required scanning.

Q5: Can I perform internal scans myself without hiring a vendor?
A: Yes, but the personnel conducting scans must be properly qualified and organizationally independent from those managing the scanned systems. Many organizations find it more cost-effective to outsource this function.

Conclusion

Understanding the differences between internal and external PCI scans is crucial for maintaining compliance and securing cardholder data. While external scans provide an attacker’s-eye view of your internet-facing infrastructure and must be performed by an ASV, internal scans offer deep visibility into your cardholder data environment and can be conducted by qualified internal staff or third parties.

Most organizations require both types of scans, performed quarterly at minimum. The key is to understand your specific requirements based on your SAQ type, implement a consistent scanning program, and maintain a robust remediation process for addressing discovered vulnerabilities.

Remember that scanning is just one component of PCI compliance—it works hand-in-hand with other security controls to protect cardholder data and maintain customer trust.

Ready to simplify your PCI compliance journey? Determining your exact scanning requirements starts with identifying your correct SAQ type. Try our free PCI SAQ Wizard tool at PCICompliance.com to instantly determine which SAQ applies to your business and get a customized compliance roadmap. With PCICompliance.com’s affordable tools, expert guidance, and ongoing support, thousands of businesses achieve and maintain PCI DSS compliance with confidence. Start your compliance journey today!