5 Reasons PCI ASV Scans Fail (and How to Avoid Them)

Failing a PCI ASV scan can be frustrating, especially when you've put time and effort into securing your environment. But a failed scan doesn't necessarily mean there's a major security problem. A single overlooked vulnerability could be enough to prevent a passing result.

Keeping on top of these issues isn't always straightforward. Internet-facing environments change constantly, and new services or configuration changes can introduce problems that aren't immediately obvious.

The good news is that many of these issues are relatively straightforward to identify and address. By understanding the common reasons organizations fail ASV scans, you can spot potential problems before your next scan, avoid unnecessary remediation work and improve your chances of passing first time.

And if you encounter any issues, please reach out. Outpost24 has several qualified assessor employees and we can guide you through the process for a smooth review, saving you effort on your compliance journey.

1. Outdated Software and Missing Security Patches

It's easy to focus on keeping your main applications up to date while overlooking the infrastructure that supports them. But ASV scanners check for known vulnerabilities across all externally detectable services on in-scope systems, not just the applications you use every day.

This means a fully patched web application could still fail an ASV scan because it's running behind a vulnerable reverse proxy, on an outdated operating system or alongside an unpatched SSH service.

Just one vulnerability with a CVSS base score of 4.0 or higher is generally enough to cause a failed scan. Certain conditions, such as unsupported operating systems, also result in an automatic failure.

How to Prevent Outdated Software from Causing an ASV Scan Failure

• Maintain an accurate inventory of all in-scope Internet-facing systems and services.
• Track vendor support and end-of-life dates, not just CVEs.
• Keep operating systems, web servers, reverse proxies and other exposed services patched, not just your main applications.
• Verify patches before the scheduled ASV scan rather than waiting for scan results to identify missing updates. With Outpost24's PCI, you can verify and scan your scope until you are ready, but make sure to account for remediation and validation time.
• Retain vendor evidence where security fixes have been backported without an obvious version change.

2. Weak TLS and Cryptographic Configuration

Even if your applications are securely configured, weaknesses in the encrypted connections they rely on can cause an ASV scan to fail. Common findings include:

• Obsolete SSL or early TLS protocols.
• Weak cipher suites.
• Certain certificate configuration problems.

PCI DSS doesn't mandate a specific TLS version. Instead, it requires strong cryptography and secure configurations. However, PCI SSC makes it clear that SSL and early TLS, including TLS 1.0 and 1.1, don't meet this standard.

How to Prevent TLS Issues from Causing an ASV Scan Failure

• Test your TLS configuration from the public Internet rather than relying solely on internal server settings.
• Check all TLS termination points, including load balancers, reverse proxies and CDNs.
• Disable outdated SSL/TLS protocols and weak cryptographic algorithms.
• Regularly review supported cipher suites to make sure they remain secure.
• Monitor TLS certificates for expiry, validity, and revocation status.
• Recheck your externally visible TLS configuration after making changes to firewalls, load balancers, or CDNs.
• Ensure you configure valid hostnames in the scanner, otherwise it can not verify that the correct certificates are used, or even see your applications.

3. Unnecessary Open Ports and Insecure Internet-Facing Services

An organization will typically need to expose some services to the Internet. Problems arise when it exposes more services than intended, or when legitimate services are configured insecurely.

An open port won't automatically cause an ASV scan to fail. However, vulnerabilities in exposed services can lead to a failed scan. Certain configurations also result in automatic failure, including direct Internet access to systems that store cardholder data, such as database servers.

In short, every Internet-accessible service should have a documented purpose and a securely maintained configuration.

How to Avoid Unnecessary Internet Exposure

• Keep an approved list of Internet-facing services and ports, with a clear business reason for each.
• Regularly review firewall rules and cloud security groups, removing temporary access when it's no longer needed.
• Make sure systems storing cardholder data aren't directly accessible from the Internet.
• Restrict access to management interfaces rather than exposing them publicly.
• Harden and regularly patch services that genuinely need to be Internet-facing.
• Run external scans between scheduled ASV scans to identify unexpected exposure and configuration changes.

4. Web Application Vulnerabilities

ASV testing includes checks for vulnerabilities and configuration weaknesses in Internet-facing web applications, not just the infrastructure they run on. Any SQL injection, cross-site scripting (XSS), directory traversal and HTTP response splitting or header injection findings are treated as automatic failures. ASV testing also checks for issues like insecure web configurations and information leakage.

These problems aren't always found in your main website or application. An outdated API endpoint that rarely gets used could still contain exploitable vulnerabilities. Similarly, a forgotten test page or detailed application error message could reveal information that's useful to an attacker.

How to Mitigate the Risk of Vulnerabilities Causing an ASV Scan Failure

• Build secure coding practices and code reviews into your development process.
• Test web applications for vulnerabilities before deployment and after major updates.
• Validate user input and use appropriate protections, such as parameterized queries and context-appropriate output encoding.
• Keep application frameworks and third-party dependencies up to date.
• Remove unnecessary test pages, debugging tools, and default content from production environments.
• Review exposed APIs and retire outdated or unused versions.
• Use ASV scanning alongside broader application security testing to identify vulnerabilities that automated external scans might miss.
• If you depend on external java-script libraries, if they are assigned a CVE, update them or prepare a dispute basis on whether vulnerable functions are used or not.

5. Security Controls Interfering with the Scan

Security tools designed to protect your systems can sometimes get in the way of an ASV scan. Web application firewalls (WAFs), intrusion prevention systems (IPS) and other protective controls may block scanning traffic, preventing the ASV from getting an accurate view of your environment. This is known as "scan interference".

The problem isn't necessarily the security tools themselves, but how they respond to scanning activity. For example, an IPS might detect a scan and temporarily block all traffic from the ASV's IP address. Similarly, a WAF might allow the first few requests before blocking further traffic once a threshold is reached.

If these controls prevent the ASV from completing a reliable assessment, the scan can't be considered a pass simply because no vulnerabilities were found. An inconclusive scan that remains unresolved must be reported as a failure.

How to Prevent Security Tooling from Disrupting a Scan

• Confirm your ASV's scanner IP addresses or ranges before testing and add those in allow-lists for any reactive protections.
• Review WAF, IPS, firewall, and CDN settings for automatic blocking, rate limiting, and other potential sources of interference.
• Work with your ASV to identify any temporary configuration changes needed to allow the scan to run without interference. Make sure to restore them once the scan is complete.
• Coordinate the scan with relevant infrastructure providers and schedule it during an agreed maintenance window where appropriate.
• Keep security controls that consistently block malicious traffic in place where possible, rather than disabling protections unnecessarily.
• Never turn off protection such as firewalls, antivirus or ACLs that are static controls to facilitate the vulnerability scanning.

How Outpost24 Helps Organizations Meet PCI Compliance Requirements

Outpost24 PCI helps you prove compliance with certified scanning and testing built around your business. Flexible scan scheduling and actionable insights make it easier to track findings, prioritize remediation, and reduce the manual effort involved in keeping your PCI program on track. We also offer a self-service option for PCI ASV scanning, simplifying compliance for organizations falling under SAQ A obligations.

With over 20 years of experience as a PCI Approved Scanning Vendor and a team of dedicated experts, Outpost24 helps organizations simplify PCI compliance management. Book a demo and see how our experts can support the scanning, testing and reporting your organization needs.