XSS in Lovable Apps
Lovable generates React code from natural language prompts, but the AI often outputs components that render user input without sanitization. This creates cross-site scripting vectors that attackers actively scan for.
Scan Your Lovable AppHow It Happens
Lovable builds React components quickly, but its AI tends to use dangerouslySetInnerHTML when prompts mention rendering rich text, markdown, or HTML content. The generated code rarely includes DOMPurify or any sanitization layer. Because Lovable apps are often built by non-developers, prompts like "show the user's bio with formatting" produce code that directly injects HTML strings into the DOM. The AI interprets "formatting" as raw HTML rendering rather than a safe markdown parser. Another common pattern is Lovable generating URL parameters that get reflected into the page without encoding. Search pages, filter UIs, and preview components are frequent offenders because the AI focuses on making things work rather than making them safe.
Impact
An attacker who finds XSS in a Lovable app can steal session tokens stored in localStorage (which Lovable/Supabase apps commonly use), redirect users to phishing pages, or modify what the victim sees on screen. Because many Lovable apps handle sensitive data through Supabase, a single XSS vulnerability can be chained with the Supabase anon key (visible in the frontend) to make authenticated API calls as the victim. This effectively gives the attacker full access to the victim's data. For apps with payment flows, XSS can be used to swap out Stripe payment links or skim credit card details from checkout forms.
How to Detect
Look for dangerouslySetInnerHTML in the built JavaScript bundle. In Lovable apps, open DevTools, search the Sources tab for "dangerouslySetInnerHTML" and trace what data flows into it. Test URL parameters by injecting a harmless payload like ?q=<img src=x onerror=alert(1)> on any page that reflects query strings. Check search bars, filter parameters, and preview URLs. Vibe App Scanner automatically detects these patterns by analyzing the deployed JavaScript bundle and testing reflected input vectors across all routes.
How to Fix
Replace every instance of dangerouslySetInnerHTML with a sanitization library. Install DOMPurify and create a wrapper component that all rich text rendering flows through. For markdown content, switch from raw HTML injection to a library like react-markdown which renders safe React elements instead of raw HTML strings. Audit all places where URL parameters or user input appear in the rendered page. Use proper React text nodes (curly braces in JSX) instead of string concatenation, which automatically escapes HTML entities. Set a Content-Security-Policy header that blocks inline scripts as a defense-in-depth measure. Even if an XSS vector exists, CSP can prevent it from executing.
Code Examples
Rendering user-generated content
<div dangerouslySetInnerHTML={{ __html: userBio }} />import DOMPurify from 'dompurify'
<div dangerouslySetInnerHTML={{
__html: DOMPurify.sanitize(userBio)
}} />Frequently Asked Questions
Does React prevent XSS automatically?
React escapes content in JSX expressions by default, but dangerouslySetInnerHTML bypasses this protection entirely. Lovable frequently generates code using dangerouslySetInnerHTML for rich text, which removes React's built-in XSS protection.
Can Supabase RLS protect against XSS?
No. RLS protects database rows from unauthorized access, but XSS runs in the context of an already-authenticated user. The attacker inherits the victim's session and RLS sees them as a legitimate user.
How quickly should I fix XSS in my Lovable app?
Immediately. XSS is a critical severity vulnerability. Automated scanners constantly probe public web apps, and Lovable apps are easy to identify from their common Supabase patterns, making them attractive targets.
Related Security Resources
Is Your App Vulnerable?
VAS automatically scans for cross-site scripting (xss) and other security issues in Lovable apps. Get actionable results with step-by-step fixes.
Scans from $5, results in minutes.