Introduction
You’ve vetted your payment provider. You follow OWASP guidelines. You even run backend vulnerability scans regularly.
But attackers are now breaching you through someone else’s code — code you include from third-party domains, CDNs, and tracking services.
Client-side supply chain attacks are on the rise, and traditional security tools don’t catch them. This post explains how they work, why they’re growing, and how you can defend against them.
What Is a Client-Side Supply Chain Attack?
A client-side supply chain attack targets code that runs in the user’s browser, usually from a third party you’ve embedded:
- Analytics platforms
- A/B testing tools
- Advertising scripts
- Form validation libraries
- Fonts and UI toolkits
Attackers compromise one of these providers, inject malicious code, and suddenly your site is skimming credit card numbers — even though you didn’t change a thing.
Notable Real-World Examples
- British Airways: Over 380,000 customers affected when a third-party script was modified to capture payment info.
- Ticketmaster: Magecart exploited a chatbot integration to exfiltrate data silently during checkout.
- Newegg: Malicious JavaScript injected into a payment iframe, affecting thousands of users.
All of these attacks occurred on the client-side, bypassing traditional WAFs, endpoint scanners, and SIEMs.
Why These Attacks Are Increasing
- More Dependencies: Modern websites use dozens of third-party libraries.
- Wider Attack Surface: Each dependency can update without your knowledge.
- No Visibility: Most teams don’t monitor what’s happening in the browser.
- No Change Control: CDNs and scripts update outside of your CI/CD pipeline.
Why Traditional Defenses Fail
Your firewall doesn’t see it.
Your endpoint protection can’t scan the user’s browser.
Your DevSecOps pipeline didn’t approve the CDN change.
Client-side supply chain attacks occur entirely outside your backend infrastructure. That’s why they’re so dangerous.
How Breachfin Stops Them
Breachfin solves this by focusing entirely on browser-side integrity:
- Scans your site in real-time from a user perspective.
- Hashes all loaded JavaScript files.
- Alerts when a known script changes — even from the same URL.
- Detects dangerous patterns like eval() or high entropy obfuscation.
- Logs every DOM change for audit tracking.
You regain control over what’s actually running in your user’s browser.
Final Thoughts
You may trust your own developers. But can you trust:
- A CDN you don’t own?
- An ad network using dozens of partners?
- A vendor that updates their script weekly?
Supply chain attacks don’t need to breach you directly. They just need to breach someone you’ve implicitly trusted.
With Breachfin, you can monitor that trust — and respond before it turns into a breach.
