Claude Code ui

XSS Vulnerability in Template Output

User-provided content displayed in template without escaping. Attacker can inject malicious JavaScript that executes in other users' browsers. Form submissions, comments, or user profiles become attack vectors.

Template renders user input directly, trusting it's safe when it's not.

Error Messages You Might See

XSS vulnerability detected in template Malicious script executed in user context Script injection through unsanitized output
XSS vulnerability detected in templateMalicious script executed in user contextScript injection through unsanitized output

Common Causes

  1. Raw HTML output without escaping: {{ userInput }} instead of properly escaped
  2. dangerouslySetInnerHTML or equivalent used without validation
  3. Server trust user input without sanitizing
  4. Missing Content Security Policy headers
  5. Frontend sanitization only, no backend validation

How to Fix It

Escape all user input by default. Use framework features: React auto-escapes, use innerText not innerHTML. Sanitize HTML: DOMPurify library on frontend. Backend validation required too. Use Content Security Policy header to block inline scripts. Never use dangerouslySetInnerHTML unless absolutely necessary and content is verified safe.

Real developers can help you.

Tejas Chokhawala Tejas Chokhawala Full-stack engineer with 5 years experience building production web apps using React, Next.js and TypeScript. Focused on performance, clean architecture and shipping fast. Experienced with Supabase/Postgres backends, Stripe billing, and building AI-assisted developer tools. Dor Yaloz Dor Yaloz SW engineer with 6+ years of experience, I worked with React/Node/Python did projects with React+Capacitor.js for ios Supabase expert David Olverson David Olverson Solo dev shipping production apps with AI-assisted development. I specialize in rescuing broken Lovable/Bolt/Cursor builds and taking them to production. 10+ apps shipped including SaaS CRMs, gaming platforms, real estate tools, and Discord bots. Stack: Next.js 16, TypeScript, Tailwind CSS, FastAPI, PostgreSQL, Prisma. I use Claude Code with 50+ custom skills for rapid delivery. Average turnaround: 2-4 weeks from broken prototype to production. Prakash Prajapati Prakash Prajapati I’m a Senior Python Developer specializing in building secure, scalable, and highly available systems. I work primarily with Python, Django, FastAPI, Docker, PostgreSQL, and modern AI tooling such as PydanticAI, focusing on clean architecture, strong design principles, and reliable DevOps practices. I enjoy solving complex engineering problems and designing systems that are maintainable, resilient, and built to scale. ISHANTDEEP SINGH ISHANTDEEP SINGH Senior Software Engineer with 7+ years of experience in React, JavaScript, TypeScript, Next.js, and Node.js. I’ve also worked as a tech lead for startups, owning end-to-end technical execution including architecture, development, scaling, and delivery. I bring a strong mix of hands-on coding, product thinking, and technical leadership, and I’m comfortable building products from scratch as well as improving and scaling existing systems. Franck Plazanet Franck Plazanet I am a Strategic Engineering Leader with over 8 years of experience building high-availability enterprise systems and scaling high-performing technical teams. My focus is on bridging the gap between complex technology and business growth. Core Expertise: 🚀 Leadership: Managing and coaching teams of 15+ engineers, fostering a culture of accountability and continuous improvement. 🏗️ Architecture: Enterprise Core Systems, Multi-system Integration (ERP/API/ETL), and Core Database Structure. ☁️ Cloud & Scale: AWS Expert; architected systems handling 10B+ monthly requests and managing 100k+ SKUs. 📈 Business Impact: Aligning tech strategy with P&L goals to drive $70k+ in monthly recurring revenue. I thrive on "out-of-the-box" thinking to solve complex technical bottlenecks and am always looking for ways to use automation to improve business productivity. Vlad Temian Vlad Temian 15+ years shipping production infrastructure for startups. Former CTO at qed.builders (acquired by The Sandbox). Cursor ambassador and agentic tooling builder. I've scaled systems, automated deployments, and built observability tools for AI coding workflows. I specialize in taking vibe-coded apps from broken prototype to production-ready: fixing Supabase auth/RLS, Stripe integrations, deployment pipelines, and cleaning up AI-generated spaghetti. I build tools in this space (agentprobe, claudebin, micode) and understand both sides: how AI generates code and why it breaks. https://blog.vtemian.com/ Krishna Sai Kuncha Krishna Sai Kuncha Experienced Professional Full stack Developer with 8+ years of experience across react, python, js, ts, golang and react-native. Developed inhouse websearch tooling for AI before websearch was solved : ) Costea Adrian Costea Adrian Embedded Engineer specilizing in perception systems. Latest project was a adas camera calibration system. Alvin Voo Alvin Voo I’ve watched the tech landscape evolve over the last decade—from the structured days of Java Server Pages to the current "wild west" of Agentic-driven development. While AI can "vibe" a frontend into existence, I specialize in the architecture that keeps it from collapsing. My expertise lies in the critical backend infrastructure: the parts that must be fast, secure, and scalable. I thrive on high-pressure environments, such as when I had only three weeks to architect and launch an Ethereum redemption system with minimal prior crypto knowledge, turning it into a major revenue stream. What I bring to your project: Forensic Debugging: I don't just "patch" bugs; I use tools like Datadog and Explain Analyzers to map out bottlenecks and resolve root causes—like significantly reducing memory usage by optimizing complex DB joins. Full-Stack Context: Deep experience in Node.js and React, ensuring backends play perfectly with mobile and web teams. Sanity in the Age of AI: I bridge the gap between "best practices" and modern speed, ensuring your project isn't just built fast, but built to last.

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Frequently Asked Questions

How to prevent XSS in React?

React auto-escapes by default. Avoid: dangerouslySetInnerHTML. For HTML content, use DOMPurify: purify.sanitize(html)

What should be escaped?

All user input, especially from forms, URLs, file uploads. Escape: <, >, &, ", ' to &lt;, &gt;, etc.

What's Content Security Policy?

HTTP header restricts script execution: Content-Security-Policy: script-src 'self'. Blocks inline scripts and external URLs.

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