By the Breachfin Team
Published: July 21, 2025
Introduction
In recent years, Magecart attacks have become synonymous with web-based credit card theft. These attacks are subtle, powerful, and devastating—quietly siphoning payment data from unsuspecting users during checkout.
What started as simple skimming scripts injected into poorly secured websites has now evolved into a sophisticated ecosystem of supply chain attacks, third-party script poisoning, and client-side evasions.
In this post, we’ll explore how Magecart has evolved and why securing the client side—specifically JavaScript—is now a critical priority for every online business.
A Quick Primer: What Is Magecart?
Magecart refers to a set of cybercriminal groups that specialize in stealing credit card data by injecting malicious JavaScript into e-commerce checkout pages.
The name came from early attacks on Magento-based storefronts, but today’s Magecart campaigns target any platform, from WordPress to Shopify to fully custom builds.
Once embedded, the malicious script waits for users to input their card information, captures it silently, and transmits it to an external server—often in real time.
Phase 1: Simple On-Site Injection
In early Magecart campaigns, attackers exploited poorly secured admin panels or outdated CMS plugins to gain write access to frontend files.
Once inside, they appended a malicious <script> tag directly to the checkout page. These were easily spotted, hardcoded, and often reused across multiple campaigns.
Example pattern:
<script src="https://malicious-domain.com/skimmer.js"></script>
These early attacks succeeded due to basic hygiene failures—lack of file integrity monitoring, weak admin credentials, and no deployment change controls.
Phase 2: Third-Party Supply Chain Attacks
As detection tools improved, Magecart groups shifted to supply chain infiltration. Instead of targeting individual sites, they breached widely used vendors—analytics tools, chat widgets, even advertising CDNs.
By injecting malicious code into trusted third-party scripts, they bypassed local protections. Victim websites loaded the infected code unknowingly—because the source was “trusted.”
Even sites with strong internal security were affected.
Notable Example:
British Airways, 2018 — attackers compromised a third-party library and skimmed payment details for over 380,000 customers.
Phase 3: Obfuscation, Entropy, and Evasion
Modern Magecart scripts are no longer obvious or static. They now use:
- High entropy strings to evade signature-based detection
- Base64 encoding to hide payloads
- Inline script injection to bypass CSP
- Browser fingerprinting to selectively target real users (not bots)
These techniques allow malicious scripts to blend in and avoid detection for weeks or months.
Why Traditional Scanners Fail
Most vulnerability scanners focus on backend configurations—SSL status, open ports, outdated libraries. But Magecart operates entirely in the client-side browser context.
Traditional tools don’t:
- Analyze JavaScript loaded at runtime
- Detect script hash changes
- Measure entropy or flag suspicious patterns
- Alert in real time
That’s why companies need client-side monitoring tools designed to see what the browser sees—not just what the server sends.
How Breachfin Helps Detect Magecart-Like Behavior
Breachfin was built to detect the exact kinds of behaviors Magecart attackers rely on:
- JavaScript hash tracking: See when trusted scripts change
- Entropy scoring: Identify obfuscated or compressed code
- Dangerous pattern detection: Flag use of
eval(),Function(), or suspicious DOM access - Historical baselines: Compare current scans with clean versions
- Real-time alerts: Notify your team immediately when script integrity breaks
Even if an attacker compromises a trusted CDN, Breachfin will catch the deviation.
Final Thoughts
Magecart attacks aren’t going away. They’re evolving—with more stealth, broader reach, and greater technical sophistication. As more checkout pages rely on dozens of external services, the attack surface keeps growing.
It’s no longer enough to secure your backend. You must monitor the client side, and specifically the JavaScript your users execute in their browsers.
If you’re not doing that, you’re operating with a blind spot—and that’s exactly where Magecart thrives.
Want to know if your scripts are safe?
Start a free scan today at breachfin.com and gain full visibility into your payment page integrity.
