React Conqued XSS? Think about it again. This is the reality facing JavaScript developers in 2025, bypassing the very framework designed to help attackers quietly evolve their injection technology to leverage everything from prototype pollution to AI-generated code and keep their applications safe.
A complete 47-page guide with framework-specific defenses (PDF, free).
JavaScript conquered the web, but with its victory, a new battlefield was born. While developers embraced React, Vue, and Angular, attackers evolved their tactics, leveraging rapid infusions of AI, compromised supply chains, and prototype pollution in ways that traditional security measures cannot grasp.
Wake Up Call: Polyfill.io Attack
In June 2024, one JavaScript injection attack compromised over 100,000 websites in the biggest JavaScript injection attack of the year. Polyfill.io’s supply chain attack, which has obtained a trusted JavaScript library and acquired weapons to inject malicious code, has affected major platforms such as Hulu, Mercedes-Benz and Warnerbros. This was not an isolated incident targeting vulnerable forms or outdated systems. This was a sophisticated injection, transforming into a website security tool against them, proving that traditional JavaScript defenses have become dangerously outdated.
The threat landscape has changed
The days when simple innentml disinfection can keep your apps safe are gone. Today’s attackers are taking advantage of:
The supply chain is targeting prototype pollution attacks targeting your favorite NPM packages. This hijacks AI-driven prompt injections across the object model that LLM tricks, generating malicious code DOM-based XSS in single-page applications that bypass server-side protection
The numbers tell the story. 22,254 CVEs were reported in mid-2024, jumping 30% from 2023 and 56% from 2022. 98% of websites using the JavaScript client side and 67.9% of developers rely on it as their main language.
This is different
Most security guides focus on attack patterns from 10 years ago. This comprehensive analysis breaks down modern threats with a detailed approach that prioritizes impact protection.
See the complete guide for actual code samples and prioritized roadmap
Framework reality check
Even the latest frameworks are not bulletproof:
This React code looks safe, but it’s not –
//Vulnerability: No salvation input
A better approach with proper disinfection –
// secure: respond to components using dompurify
Why is it important:
By injecting HTML directly into the DOM, you risk React’s built-in XSS protection by injecting HTML directly. If your user content contains malicious scripts, run them immediately in the victim’s browser.
Perform actions on behalf of the authenticated cookie and session token user and redirect to a malicious site
Dompurify sanitizes HTML by parsing content and removing potentially malicious elements.
etc.
Banking sector under siege
The financial industry has become a major target for sophisticated JavaScript injection attacks. In March 2023, IBM discovered malware campaigns targeting more than 40 banks in the US, Europe and Japan, compromising over 50,000 individual user sessions. The attack leveraged advanced JavaScript web injection, which detects specific page structures used by banking platforms, and then dynamically injected malicious scripts to steal user credentials and one-time password tokens.
What made the campaign particularly dangerous was its adaptive behavior, where the malware always communicated with the command and control server, adjusting tactics in real time based on page state and security detection attempts. Using sophisticated obfuscation techniques, malware can patch features to remove traces of its existence and avoid running when a security product is detected, demonstrating that traditional JavaScript defenses do not match the latest dynamically evolving threats.
RAW, encoded with output principle
One of the most practical insights in the guide is to enhance basic security best practices. Always store raw data and encode it based on the output context.
This approach:
Data that stores unincoded Raw data in the database applies context-specific encoding to render times based on where the data is displayed. Each output context (HTML entities in HTML content, JavaScript in JS context escapes, URL encoding in URL, CSS in StyleSheets escapes)
This context-aware encoding approach prevents dual encoding problems, maintains data integrity, and ensures proper protection regardless of how the data is ultimately displayed. An important insight is that the same user input may require HTML encoding when it appears in the DIV. JavaScript escapes when used with script tags, and URL encoding is required when used with link parameters.
WebAssembly Security Considerations
While WebAssembly offers performance benefits and sandboxing, it is important to understand the security implications. The guide considers how WASM implements specific considerations that developers should recognize.
Carry over source code vulnerabilities: Memory such as C/C++ compiled to WASM – non-safe languages retain original vulnerability patterns (buffer overflow, waste, etc.) Reduces transparency: Binary format makes security auditing more difficult compared to source new attack surfaces in easy-to-read Javascript sources.
WebAssembly’s sandboxed execution model provides strong separation, but like any other technology, it requires thoughtful implementation and should not be considered an automatic security upgrade from JavaScript.
New AI threats
When LLMS was integrated into web applications, a new attack vector appeared: rapid injection attacks. Malicious users will encourage them to create a Trick AI model to generate JavaScript code that runs on the client side. Find out more in the complete guide.
Conclusion
Modern JavaScript security is not about checklist implementations, but about understanding how attackers think and build layered defenses that adapt to evolving threats. Whether you build it in React, Angular or Vue, the basic principles remain. Do not trust client-side code. Always validate the server side and encode it based on context.
The complete guide provides examples of implementations of all the key frameworks, practical code samples, and prioritized approaches that will help your team tackle the most important vulnerabilities first.
Download the complete PDF playbook here.
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