Most security tools can't see inside the browser, where attackers hide malicious code in website scripts that go unmonitored.
A single compromised script can skim data for weeks, staying hidden from traditional security tools
CSPs, Crawlers, and JS agents were built for static threats. Modern attacks evade these approaches with dynamic code.
PCI DSS 4.0.1 requires client-side monitoring. GDPR penalizes companies for data leaks from malicious or misconfigured scripts.
Select the method that best fits your security needs and technical requirements.
"I care about client-side security and I need something that will be easy to explain to the rest of the team."
We check script behaviors in the browser and fetch the scripts on our side. We don't place ourselves in the path of a script unless you explicitly ask us to.
Operating Model
Allow the script to serve directly for scripts I trust, scripts I don't trust get the full security treatment.
"I don't have the ability to add a script to the website."
cside threat intel gathered by thousands of other websites with combined billions of visitors.
Operating Model
Static scanning powered by threat intelligence from our network.
Unlike modern operating systems, browsers do not have native support for 3rd party security vendors. CSP and SRI only cover so much, so we got to get creative. Most client-side detections using JavaScript in the browser are easy to reverse engineer and circumvent. Unfortunately, too strict client-side detections could break some client-side libraries. What a script for client-side security does is wrap APIs that can be used by bad actors and monitor which scripts use them. The problem is that not every script plays nicely with that. So for that reason, we've taken a much more elaborate approach for the most security conscious users. By combining the detections in the browser with detections on our own engine we create a balanced best of all worlds scenario. Balancing detection ability with ease of use with resilience and ultimately giving the customer the ability to choose the approach.
Our approach delivers advantages traditional tools can't match. We combine real user sessions with AI powered script analysis to gain a complete view of script behavior.
| Feature | cside | Traditional Solutions |
|---|---|---|
| Real User Monitoring | Sees actual user behavior and script execution in production | Crawlers only see sanitized versions of scripts |
| Targeted Attack Detection | Catches attacks aimed at specific user segments or time periods | Misses attacks between periodic scans |
| Script Security & Analysis | Monitors actual script payloads and behavior in real-time, ensuring script integrity | Only checks script sources, not what they do |
| Third-Party Risk | Detects when trusted providers are compromised | Assumes trusted sources are always safe |
| Dynamic Scripts | Handles dynamically generated and obfuscated code | Limited control over dynamic script execution |
| Attack Prevention | Analyzes scripts server-side where attackers can't interfere | Client-side analysis vulnerable to tampering |
| Historical Tracking | Complete audit trail of script behavior over time | Limited or no historical script tracking |
| Future-Proofing | Adapts to new attack techniques automatically | Requires updates to detect new threats |
FAQ
Frequently Asked Questions
Client-side security protects users from threats that occur directly in their browser while visiting websites, particularly from malicious third-party scripts and dependencies. These scripts can steal credit card details, personal information, session tokens, and cause major compliance violations without your knowledge. Unlike server-side attacks that target your infrastructure, client-side attacks happen in real-time within users' browsers, making them invisible to traditional security tools like firewalls and server monitoring systems.
Modern websites use JavaScript files from external sources for functionality, analytics, advertising, and user experience enhancements. These files are also called third-party scripts. These scripts are important to improve website performance, but just one malicious script can wreak havoc on your platform. It can skim credit card details (Magecart attacks), steal login credentials and personal information, inject malicious redirects, and hijack user sessions. The problem with scripts is the fact that they have full website privileges, so by default, they have access to everything users see and input on your pages.
They can attack supply chains, take over CDN domains, or inject malicious code into legitimate scripts. Any of these entry points can allow attackers to steal payment data in real-time, redirect users to malicious sites, capture form inputs and passwords, or inject fake payment forms. These attacks are conditional: they target specific users or activate at certain times, dodging security tools that rely on periodic scans.
Two major examples: the British Airways Magecart attack in 2018 and the 2024 Polyfill.js hijack. In the British Airways attack, compromised third-party scripts stole credit card details from over 380,000 customers, leading to fines exceeding $200 million. The Polyfill.js hijack let attackers take over a widely-used CDN domain, redirecting users on over 100,000 websites to adult and betting sites. One compromised script can impact millions of users.
Firewalls, server monitoring, and endpoint protection guard the server-side. Client-side attacks happen in users' browsers, where those tools are blind. Worse, these attacks are targeted and conditional: they can single out one user or fire only under specific conditions, running for weeks while affecting real visitors undetected.
Financial websites are a gold mine for malicious third-party scripts. They can steal login credentials, personal information like SSNs and addresses, account numbers, transaction data, and payment details. This can be done by intercepting form submissions, capturing keystrokes, accessing browser storage, manipulating pages to create fake forms, and bypassing security measures. Because these scripts have full website privileges, they're dangerous for any financial site.
According to Visa, 70% of all credit card theft now happens on the client-side. Server-side defenses alone aren't enough. Attackers have already shifted their focus to the browser, and businesses need client-side solutions to match.
Can your security tools show exactly what data each third-party script collects, or can they detect a malicious payload that fires for only 1 in 1,000 visitors or targets just 5% of users after 5 p.m.? If you're one of the 99% of companies that answer NO to this question, then you're vulnerable to sophisticated, conditional client-side attacks.