Security teams protecting websites face a visibility challenge. Traditional tools secure servers and network traffic but cannot see what happens after pages load in users’ browsers. For websites processing payments, this blind spot creates significant risk. IBM’s 2025 breach report shows organizations take an average of 241 days to identify breaches, while Verizon’s 2025 DBIR found 30% of breaches involve third-party components.
Payment page attacks target JavaScript executing in browsers, where Web Application Firewalls have no visibility and code scanning tools cannot reach. These 10 strategies address the client-side security gap that enables Magecart, formjacking, and web skimming attacks.
1. Maintain comprehensive script inventory
Document every JavaScript resource loaded on your payment pages. Catalog what each script does, what data it accesses, and which vendor provides it. You cannot authorize scripts you have not identified, and you cannot detect unauthorized changes without knowing what should be present.
This inventory forms the foundation for PCI DSS 6.4.3 compliance, which mandates that payment page scripts are managed and authorized. Manual spreadsheets quickly become outdated. Automated inventory tools that continuously discover and catalog scripts provide accurate, current visibility.
2. Implement real-time behavioral monitoring
Track JavaScript execution patterns, DOM manipulation, form field access, network requests, and data flows within the browser. Behavioral monitoring detects suspicious activities regardless of whether malicious code appears in threat databases.
Warning signs include unauthorized payment form access, unexpected data collection patterns, unusual network communications, and scripts executing outside defined parameters. Traditional signature-based detection fails against client-side threats because attacks evolve faster than signature databases update.
3. Deploy automated change detection
Monitor for script modifications, new script additions, and alterations to payment page code. Client-side attacks often involve adding new scripts or modifying existing ones. Automated detection that alerts on changes provides early warning of potential compromise.
PCI DSS 11.6.1 requires detecting and reporting unauthorized changes to payment page scripts. Manual review processes do not satisfy this requirement. You need systems that run continuously and alert security teams when modifications occur.
4. Assess third-party script providers
Evaluate security practices of vendors providing scripts for payment pages. Review their software development security practices, incident response capabilities, and notification procedures for security issues. Understand how they handle security updates and what your responsibilities are for deploying those updates.
The 2018 British Airways breach occurred when attackers compromised a third-party script loaded on payment pages, harvesting 380,000 payment cards over several months. Loading third-party code on payment pages means trusting that vendor with your customer payment data.
5. Configure Content Security Policy
Implement CSP headers that restrict which scripts can execute on payment pages. Content Security Policy provides defense-in-depth by defining approved sources for scripts, styles, and other resources. When properly configured, CSP can block unauthorized code execution even if attackers inject malicious scripts.
Start with restrictive policies and expand as needed. Use nonces or hashes for inline scripts instead of unsafe-inline directives. Monitor CSP violation reports to identify both potential attacks and legitimate functionality needing policy adjustments.
6. Implement subresource Integrity checks
Use Subresource Integrity for third-party scripts loaded from CDNs. SRI allows browsers to verify that fetched resources have not been modified by comparing cryptographic hashes. If content changes, the browser refuses to execute it.
This protects against compromised CDNs but requires updating hashes when vendors release legitimate updates. Automated tools can manage SRI implementation and maintenance, balancing security benefits with operational overhead.
7. Monitor form field interactions
Track which scripts access payment form fields and what data they collect. Legitimate payment processors need access to payment card fields. Analytics scripts typically do not. Behavioral monitoring that identifies unauthorized form access provides early detection of skimming attempts.
Payment pages represent your highest-risk client-side environment. This is where customers enter credit card numbers, CVV codes, and billing information. IBM’s 2025 research shows average breach costs of $4.4M globally and $10.22M in the U.S., with costs rising due to regulatory escalation.
8. Detect unusual network communications
Monitor JavaScript network requests during payment processing. Malicious scripts exfiltrate stolen data to attacker-controlled servers through connections that appear similar to legitimate analytics traffic. Both use HTTPS, both transmit data regularly, both generate similar patterns.
Behavioral analysis that establishes baselines for normal communication patterns can identify anomalous connections. This includes requests to unexpected domains, unusual data volumes, or communication patterns that deviate from established norms.
9. Implement continuous compliance monitoring
Map client-side security controls directly to PCI DSS requirements 6.4.3 and 11.6.1. Automate evidence collection for audits rather than scrambling to gather proof when assessments occur. Continuous monitoring provides ongoing assurance and simplifies compliance demonstrations.
Organizations handling payment card data must implement mechanisms ensuring only authorized scripts execute on payment pages and systems that detect unauthorized changes. These requirements exist because client-side attacks directly target payment processing flows.
10. Establish incident response procedures
Develop response procedures specific to client-side security incidents. Payment page breaches require different approaches than traditional server compromises. You need processes for rapidly identifying compromised scripts, removing malicious code, assessing customer impact, and meeting breach notification requirements.
Practice procedures through tabletop exercises and simulations. The middle of an actual breach is not the time to discover your runbooks are outdated or your team does not know how to execute containment procedures. The 241-day average identification time gives attackers months of access. Effective incident response reduces this window.
Moving from strategy to implementation
These ten strategies provide comprehensive client-side security for payment pages. Implementation requires continuous monitoring that observes JavaScript behavior in production environments, detects anomalies indicating potential compromise, and provides forensic information for incident response.
This visibility extends beyond meeting PCI DSS audit requirements. It enables rapid incident detection, provides evidence for demonstrating control effectiveness to auditors and regulators, and allows security teams to identify third-party script risks before they lead to breaches.
Traditional Web Application Firewalls, code scanning tools, and network monitoring cannot see attacks happening in the browser. Client-side monitoring has moved from optional to essential for organizations processing payments. Payment pages are where customers interact with your applications and entrust you with their payment information.
Feroot provides purpose-built client-side security for organizations processing payments. Our platform delivers automated monitoring, behavioral analysis, and compliance reporting that addresses PCI DSS 6.4.3 and 11.6.1 requirements while providing the real-time visibility security teams need to detect and respond to payment page threats.
If your security program needs client-side controls that extend protection to where modern attacks occur, Feroot can help you implement these strategies and build comprehensive payment page security.
