Approved Scanning Vendors (ASVs): Requirements, Whitelisting, and Finding the Right Provider

Complying with the Payment Card Industry Data Security Standard (PCI DSS) is essential for any organization that handles payment card data. One of the key requirements for maintaining PCI DSS compliance is conducting regular external vulnerability scans using an Approved Scanning Vendor (ASV). These scans help identify potential vulnerabilities in your external-facing systems before malicious actors can exploit them.

This comprehensive guide explores the PCI DSS requirements for ASV scans, the scope of these assessments, the importance of whitelisting, and how to select the right ASV for your organization.

PCI DSS Requirements for ASV Scans

Understanding Requirement 11.3.2

PCI DSS Requirement 11.3.2 (v4.0) mandates that organizations must perform quarterly external vulnerability scans via an Approved Scanning Vendor. This requirement is designed to ensure that external-facing systems are regularly checked for security weaknesses that could be exploited to gain unauthorized access to cardholder data.

According to the requirement, external vulnerability scans must be performed:

• At least once every three months (quarterly)
• By a PCI SSC Approved Scanning Vendor (ASV)
• Until vulnerabilities are resolved and ASV Program Guide requirements for a passing scan are met
• With rescans as needed to confirm that vulnerabilities are resolved per the ASV Program Guide requirements

Frequency of Scans

While the minimum requirement is quarterly scanning, more frequent scans are recommended in certain circumstances:

• After significant changes to your network infrastructure
• Following major application updates or migrations
• When deploying new systems in your cardholder data environment
• For networks with high complexity or frequent changes
• When using diverse types of devices, software, and operating systems

"While quarterly scanning is the minimum requirement, organizations with dynamic environments should consider more frequent scans to maintain a strong security posture."

What Makes a Passing Scan?

For a scan to be considered "passing," it must meet the requirements specified in the ASV Program Guide:

• No vulnerabilities rated as CVSS 4.0 or higher detected
• If vulnerabilities with CVSS scores of 4.0 or higher are detected, they must be addressed
• For certain vulnerabilities that cannot be immediately remediated, a documented risk assessment and mitigation plan may be accepted by your QSA

Your Qualified Security Assessor (QSA) may require additional documentation to verify that non-remediated vulnerabilities are in the process of being resolved according to an appropriate timeline.

Scope of ASV Scans

Determining the correct scope for ASV scans is crucial for effective security assessment and PCI DSS compliance.

What Must Be Included in ASV Scans

The scope of an ASV scan includes all external-facing components that are part of or connected to your cardholder data environment (CDE):

• Public-facing IP addresses: All IP addresses accessible from the internet
• Domain names: Any registered domains that resolve to public-facing systems
• External interfaces: Including web servers, email servers, and API endpoints
• Network perimeter devices: Such as firewalls and routers with external interfaces
• Cloud-hosted environments: External interfaces of cloud-hosted systems that process, store, or transmit cardholder data

Scope Determination Process

To accurately determine the scope of your ASV scans:

1. Identify all internet-facing systems: Create an inventory of all systems with external interfaces
2. Map data flows: Document how cardholder data moves through your network
3. Verify network segmentation: If using network segmentation to reduce PCI scope, this must be verified
4. Document all public IPs and domains: Include all possible entry points to your network
5. Consider third-party connections: Identify connections to third-party providers that may affect your CDE

Common Scope Mistakes to Avoid

Organizations often make these mistakes when determining ASV scan scope:

• Overlooking development environments that have external interfaces and may contain production data
• Missing cloud-hosted components that are part of the cardholder data environment
• Forgetting newly acquired domains or IP ranges from business changes
• Excluding temporary systems that may be exposed to the internet
• Omitting third-party connections that could provide access to the CDE

The Importance of Whitelisting for ASV Scanning

Whitelisting is a critical process that ensures your ASV can effectively scan your external-facing systems without being blocked by your security measures.

What is Whitelisting?

In the context of ASV scanning, whitelisting involves configuring your security controls to allow specific scanning traffic from your ASV's IP addresses. This process ensures that legitimate security scanning activities are not mistaken for attacks and blocked by:

• Firewalls
• Intrusion Prevention Systems (IPS)
• Web Application Firewalls (WAF)
• DDoS protection services
• Rate limiting mechanisms

Why Whitelisting is Essential

Failing to properly whitelist your ASV's scanning infrastructure can lead to:

1. Incomplete scans: Critical vulnerabilities may be missed if security controls block scanning traffic
2. False negatives: Vulnerabilities might exist but remain undetected due to blocked scans
3. Inefficient rescans: Multiple rescans may be needed if initial scans are blocked
4. Compliance issues: Incomplete scans may not satisfy PCI DSS requirements
5. Wasted resources: Time and money spent on ineffective scans

Best Practices for Whitelisting

To ensure effective ASV scans through proper whitelisting:

• Obtain a complete list of all scanning IP addresses from your ASV
• Implement temporary whitelisting only for the duration of the scanning period
• Use precise rules that allow only the specific protocols and ports needed for scanning
• Document all whitelisting changes for audit purposes
• Test whitelist configurations before the actual scan to verify access
• Remove whitelist entries after scanning is complete if they aren't needed for regular scanning

Whitelisting Without Compromising Security

It's important to implement whitelisting in a way that doesn't weaken your overall security posture:

• Limit whitelisting to only the specific ASV IP addresses provided
• Restrict access to only the protocols required for scanning (typically HTTP/HTTPS)
• Consider using time-based access rules that automatically expire
• Monitor all traffic from whitelisted IPs, even though they're trusted sources
• Review and update your whitelist regularly to remove outdated entries

How to Find and Select the Right ASV

Choosing the right Approved Scanning Vendor is crucial for effective vulnerability management and PCI DSS compliance.

Official PCI SSC List of Approved Vendors

The PCI Security Standards Council maintains an official list of Approved Scanning Vendors that have been validated to perform external vulnerability scanning services. You can access this list on the PCI Security Standards Council website.

Key Factors to Consider When Selecting an ASV

When evaluating potential ASV partners, consider these important factors:

1. Technical Capabilities

• Scanning technology: Assess the robustness of their scanning engine and detection capabilities
• False positive rate: Ask about their processes for reducing false positives
• Scan customization: Ability to tailor scans to your specific environment
• Reporting tools: Quality and usability of vulnerability reports

2. Service Offerings

• Scan scheduling flexibility: Options for scheduling scans during low-traffic periods
• Remediation support: Guidance on addressing identified vulnerabilities
• Rescanning policies: Process and limitations for verification rescans
• Additional security services: Availability of complementary services like penetration testing

3. Customer Experience

• Support quality: Availability and responsiveness of technical support
• Portal usability: Ease of use of their customer interface
• Documentation: Clarity and completeness of scanning documentation
• Onboarding process: Simplicity of getting started with their service

4. Industry Experience

• Experience with similar organizations: Familiarity with your industry and environment type
• Client references: Testimonials from organizations similar to yours
• Tenure as an ASV: How long they've been an approved vendor
• Reputation: Industry standing and reviews

5. Commercial Considerations

• Pricing structure: Clarity and fairness of pricing model
• Contract flexibility: Available contract terms and conditions
• Additional costs: Transparency about any extra fees for rescans or support
• Value-added services: What's included beyond the basic scanning requirement

Questions to Ask Potential ASV Providers

When contacting ASV vendors, consider asking these key questions:

1. "What is your process for helping clients determine the correct scan scope?"
2. "How do you handle false positives in your scanning results?"
3. "What support do you provide for remediation of identified vulnerabilities?"
4. "What is your rescanning policy and is there an additional cost for rescans?"
5. "How do you stay current with emerging vulnerabilities and threats?"
6. "What is your typical response time for technical support issues?"
7. "Can you provide references from clients in our industry?"
8. "What makes your ASV service different from other providers on the PCI SSC list?"

Implementing an Effective ASV Scanning Program

Beyond simply hiring an ASV, implementing an effective vulnerability management program requires organizational commitment and processes.

Preparing for Your First ASV Scan

Before your initial scan:

1. Document your external network: Create a comprehensive inventory of all external-facing systems
2. Perform internal scanning: Identify and fix obvious vulnerabilities before external scanning
3. Prepare your team: Ensure security staff are available during scanning windows
4. Establish remediation processes: Define workflows for addressing identified vulnerabilities
5. Set up whitelisting: Configure security controls to allow scanning traffic

Developing a Remediation Workflow

When vulnerabilities are identified:

1. Validate findings: Verify that reported vulnerabilities are real and applicable
2. Prioritize issues: Address high-risk vulnerabilities first based on CVSS scores and business impact
3. Assign ownership: Clearly designate responsibility for remediation tasks
4. Track progress: Monitor remediation efforts through completion
5. Verify fixes: Request rescans to confirm that vulnerabilities have been properly addressed

Continuous Improvement

To enhance your vulnerability management over time:

1. Trend analysis: Track vulnerability types and patterns over multiple scans
2. Root cause analysis: Identify underlying issues causing recurring vulnerabilities
3. Process refinement: Continuously improve remediation workflows and timelines
4. Knowledge sharing: Educate development and operations teams about common vulnerabilities
5. Pre-deployment scanning: Implement security testing earlier in your development lifecycle

Conclusion

ASV scanning is more than just a compliance checkbox—it's a critical component of a robust security program that helps protect your customers' sensitive payment card data. By understanding the requirements, properly defining scan scope, implementing effective whitelisting, and carefully selecting the right ASV partner, you can turn this compliance requirement into a valuable security asset.

Remember that quarterly scanning is the minimum requirement—organizations with dynamic environments or high-risk profiles should consider more frequent assessments to maintain a strong security posture.