by Source Defense
Modern websites depend on JavaScript to deliver analytics, chat, payments, and personalization. But every external script running in a customer’s browser introduces risk. Attackers exploit these scripts to perform eSkimming and formjacking, stealing sensitive data right at the point of input before it ever reaches your secure server.
This practical five step checklist outlines how your security team can quickly reduce exposure, protect customer data, and align with PCI DSS 4.0.1 requirements 6.4.3 and 11.6.1.
Step 1: Inventory All Scripts (Including Third-Party Tags)
Visibility is the foundation of security. The 2024 Verizon Payment Security Report found that the average eCommerce site loads more than 18 third and fourth-party scripts per page, many with access to payment or personal data. Without knowing what’s running on your site, you can’t confirm which scripts are authorized or even detect malicious ones.
Start by scanning every web asset to identify all scripts, including those added through analytics, marketing, and tag management tools. Identify each script whether developed internally or added by an external partner and document who added it, what data it accesses, and why it’s needed.
Use your first inventory as a baseline, then automate continuous scanning to keep it current and detect new or changed scripts as they appear. This ongoing monitoring validates that every script affecting payment pages remains authorized and documented in alignment with PCI DSS requirement 6.4.3.
Step 2: Authorize and Justify Each Script
An inventory is only valuable if each item on it has a reason to exist. PCI DSS 6.4.3 requires organizations to authorize and justify every script running on payment pages. This means confirming each script’s business purpose, data access, and source integrity.
Review and approve every script before deployment, establishing clear authorization criteria that define what’s necessary such as analytics, checkout functionality, or fraud prevention. Document each script’s role and ensure it aligns with business and security objectives. Integrate these approvals into your release cycle so new scripts can’t slip into production without oversight. Finally, remove outdated or unnecessary scripts. Every unused tag increases your attack surface and introduces unnecessary complexity.
Tip: Treat script authorization like vendor management. Each script has a lifecycle, and every update should trigger a review.
Step 3: Implement Script Integrity Controls
Even authorized scripts can be compromised. Traditional controls such as Content Security Policy (CSP) and Subresource Integrity (SRI) can contribute to a layered defense by verifying source integrity and limiting where scripts load from. However, relying on them as the only line of defense is time-consuming and difficult to maintain in modern, dynamic environments. A behavior-based security model complements these measures by continuously analyzing what scripts do inside the browser and blocking malicious actions in real time.
Use sandboxing or isolation controls to contain third-party code and prevent it from interacting with sensitive form fields. Apply behavior-based policies that automatically block scripts attempting to capture keystrokes, alter the page structure, or send data outside approved destinations. When a script tries to read form inputs, redaction can mask the data to ensure nothing sensitive is exposed.
Automate integrity validation so you receive alerts when a script’s content or behavior deviates from its baseline, and test regularly to confirm that legitimate functionality remains unaffected. Real-time behavior analysis can further simplify this process by adapting automatically to new or updated scripts, removing much of the manual effort needed to maintain policies.
Step 4: Set Up Change Detection and Alerting
Detecting unauthorized changes early is critical. PCI DSS 11.6.1 requires organizations to monitor payment pages for modifications that could expose customer data. Weekly scans are the minimum, but real-time change detection provides true protection offering instant visibility into tampering or injected scripts before data is stolen.
Set up continuous monitoring to watch your payment pages and security headers for any unexpected changes. When new or altered scripts appear, your security team should get an immediate alert and have the option to block suspicious activity automatically. Feed those alerts into your SIEM so everything shows up in one place, giving your analysts full visibility and quicker response times. Keep detailed audit logs as well—those records will support both compliance reviews and investigations.
Best Practice: Combine real-time alerts with automatic blocking to stop eSkimming and Magecart attacks before data is exposed.
Step 5: Maintain Continuous Compliance and Reporting
Security and compliance aren’t one-time projects, they’re ongoing disciplines. To sustain compliance and demonstrate control to auditors, organizations must maintain continuous visibility into script activity and behavioral trends.
Centralize your reporting to show a complete picture of your script environment, including inventory, authorization status, and recent changes. Regularly review these reports to ensure no new or unapproved scripts have been introduced. Integrate this data into your PCI DSS documentation so it supports your evidence requirements automatically.
Educate your marketing and digital teams about their role in maintaining compliance, and use automation to minimize the operational workload. Behavior-based solutions often include built-in reporting that validates compliance with PCI DSS 6.4.3 and 11.6.1 saving valuable time during assessments.
From Visibility to Control: Strengthening Security Where It Matters Most
Following these five steps Inventory, Authorize, Control, Detect, and Maintain closes one of the most persistent blind spots in web application security. It allows you to protect customer data at the point of input, prevent eSkimming attacks, and meet compliance requirements without overburdening your development or marketing teams.
Source Defense Protect automates this entire process through real-time script isolation, redaction, and monitoring. It delivers measurable PCI DSS compliance and enhanced browser security requiring less than five hours of management per month.
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PCI DSS 4.0 makes client-side security a priority.
Source Defense delivers a solution for 6.4.3 and 11.6.1 without adding a burden to your security teams.