Detect and Mitigate Client-Side Website Attacks Before They Reach Your Customers

Client-side website attacks target the code running in a visitor’s browser rather than the website’s server. Attackers exploit vulnerabilities in JavaScript and other client-side technologies — including first-party code and third-party libraries — to inject malicious scripts, skim payment data, or exfiltrate sensitive information.

Common types include:

• Web skimming (Magecart): Malicious code injected into third-party libraries or directly into pages to capture payment card data during checkout
• Formjacking: Scripts that intercept form submissions to siphon personal and financial data
• Unauthorized data collection: Third-party tags or scripts collecting data beyond their approved scope
• CSS injection: Injected style rules that can manipulate page appearance or trigger data exfiltration

These attacks are difficult to detect with server-side security alone because the malicious activity occurs entirely within the browser.

CHEQ uses Trust Intelligence — one of three layers in its triple-layer intelligence engine — to analyze what runs inside each browser session. Trust Intelligence detects:

• Malicious script and skimmer behavior in real time
• Sensitive data leakage signals from unauthorized third-party activity
• Unapproved script and vendor activity beyond approved configurations
• Consent and privacy enforcement gaps where data collection occurs without authorization

This is correlated with Traffic Intelligence (which evaluates the entity, device, and network behind each session) and Identity Intelligence (which assesses the authenticity and risk of the user behind the interaction) to provide a comprehensive view of each client-side event.

Third-party scripts — such as analytics tags, chat widgets, advertising pixels, and open-source libraries — execute in the visitor’s browser with the same access as your own code. This creates risk because:

• Third-party code can change at any time without your development team’s knowledge
• A compromised vendor can inject malicious functionality into thousands of sites simultaneously
• Scripts can access page elements, read form data, and send information to external servers
• Organizations often have limited visibility into what third-party code is actually doing in the browser

CHEQ provides client-side observability to identify all technologies running across your digital properties and detect when their behavior deviates from expected patterns.

PCI DSS requirements increasingly address client-side risks, particularly around protecting payment pages from script-based attacks. CHEQ helps support compliance by:

• Monitoring all scripts executing on payment pages and sensitive forms
• Detecting unauthorized script modifications or injections in real time
• Enforcing policies that restrict which technologies can load on specific pages
• Generating audit-ready compliance reports and evidence logs

CHEQ’s approach is designed to help organizations maintain continuous governance over the client-side environment rather than relying solely on periodic code reviews.

Server-side security protects the infrastructure, databases, and application logic that reside on your servers. Client-side security addresses threats that occur in the browser — the environment where your website is rendered and where users interact with forms, payment flows, and dynamic content.

Key differences:

• Server-side threats include SQL injection, authentication bypass, and direct data breaches
• Client-side threats include script injection, web skimming, formjacking, and unauthorized data collection by third-party code
• Server-side tools (firewalls, WAFs) do not see what happens after code is delivered to the browser
• Client-side protection requires monitoring and enforcement at the browser level, where CHEQ’s Trust Intelligence operates

Both layers are necessary. CHEQ specifically addresses the client-side gap that server-focused security tools cannot cover.

CHEQ’s client-side monitoring is designed to operate with minimal performance impact. The approach includes:

• A lightweight tag deployment that begins monitoring immediately
• Detection processing optimized for real-time analysis without adding noticeable page load latency
• Proportional enforcement options that allow you to configure responses — from monitoring to blocking — based on your specific performance and security requirements

This design reflects CHEQ’s broader principle of protection that does not compromise the customer experience.

Yes. CHEQ’s Trust Intelligence monitors all code executing in the browser session, regardless of whether it originates from first-party, third-party, or open-source sources. 

When a library’s behavior changes — for example, if an attacker injects skimming code into a widely used JavaScript package — CHEQ can detect the anomalous script behavior and data flow patterns that indicate compromise.

This is particularly important because open-source supply chain attacks can affect thousands of sites simultaneously when a single upstream library is modified.

CHEQ Enforce automatically applies consent and privacy preferences to control which scripts and tags are allowed to run. This includes:

• Blocking technologies that attempt to collect data without proper user consent
• Enforcing privacy rules dynamically across all digital assets
• Providing real-time monitoring to detect unauthorized tracking attempts
• Generating compliance evidence and audit logs for regulatory review

This helps organizations move beyond static consent banners to active enforcement of privacy preferences at the script level, supporting alignment with GDPR, CCPA, and other privacy regulations.