Stop Client-Side Attacks Before They Reach Users
Most security tools can't see inside the browser, where attackers hide malicious code in website scripts that go unmonitored.
The invisible layer
- 01
The invisible attack layer
A single compromised script can skim data for weeks, staying hidden from traditional security tools
- 02
Legacy solutions have blindspots
CSPs, Crawlers, and JS agents were built for static threats. Modern attacks evade these approaches with dynamic code.
- 03
Regulatory pressure is increasing
PCI DSS 4.0.1 requires client-side monitoring. GDPR penalizes companies for data leaks from malicious or misconfigured scripts.
- Automatically monitor what every script does and block malicious behavior instantly
- Protect users from e-skimming, Magecart, hostile redirects, and other attacks
- Adhere to PCI DSS and GDPR by enforcing strict controls on script data exposure
- Maintain script integrity and secure payment portals to protect customer trust and brand reputation
Client-side protection built for the modern web
Monitor every session
cside mirrors every live session and sees how scripts execute in your users' browser
Analyze every script
AI-powered engine de-obfuscates malicious JavaScript, ensures script integrity, and flags suspicious activity
Stop attacks
Real-time mitigation stops data exfiltration instantly, and every event is forensically logged
Catch dynamic attacks
Spot the modern attacks that evade CSPs, Crawlers, and JS Agents
Choose your security approach
Select the method that best fits your security needs and technical requirements.
Script Method
Easiest"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.
- Easiest to implement
- No performance impact
- Ability to stop script actions or block by URL, hash, or domain
- — Not always guaranteed to check the same script payload as the user got - but it's close
- — No performance gains on static or optimizable scripts
Allow the script to serve directly for scripts I trust, scripts I don't trust get the full security treatment.
Scan Method
Fastest"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.
- Cheap
- Fast and easy to setup
- — Client-side attacks are dynamic, a static scan is by design less likely to spot an attack
- — A highly targeted attack could succeed at avoiding detection
Static scanning powered by threat intelligence from our network.
Why We Approach It This Way
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.
Built for industries handling sensitive data
Payment providers
Protect sensitive payment data and meet PCI compliance.
ExploreeCommerce
Prevent card skimming and protect customer checkout flows.
ExploreHospitality
Secure booking flows and protect guest information.
ExploreHealthcare
Keep patient data private and maintain HIPAA compliance.
ExploreWhy cside outperforms every alternative
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 |
Questions, answered
01 What is client-side security and why does it matter for my website?
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.
02 What are third-party scripts and why are they risky?
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.
03 How do attackers use third-party scripts to harm users?
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.
04 What are some real-world examples of client-side attacks?
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.
05 Why don't traditional security tools catch client-side attacks?
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.
06 What data can malicious scripts steal from financial websites?
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.
07 What percentage of credit card theft now happens through client-side attacks?
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.
08 How can I tell if my current security tools can detect sophisticated client-side attacks?
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.
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