Bolt
security
Missing Input Sanitization in Bolt App Forms
Your Bolt.new application accepts user input from forms, URL parameters, and API requests without validating or sanitizing it. This leaves your app vulnerable to cross-site scripting (XSS), HTML injection, data corruption, and other attacks that exploit unfiltered input.
When Bolt generates form handling code, it often passes user input directly to the database or renders it on the page without checking for malicious content. A user could submit a script tag in a comment field, an extremely long string that breaks your layout, or special characters that corrupt your data.
The consequences range from cosmetic issues (broken layouts) to critical security breaches (stolen user sessions, defaced pages, or unauthorized data access). This is one of the most common security gaps in AI-generated applications.
Error Messages You Might See
Warning: Each child in a list should have a unique key prop
Content Security Policy violation: inline script blocked
Unhandled Runtime Error: Objects are not valid as a React child
XSS payload detected in input field
Common Causes
- No server-side validation — Form data is accepted and stored without checking type, length, or format on the backend
- Using dangerouslySetInnerHTML — Bolt generated React components that render user content as raw HTML, enabling XSS
- Client-only validation — Validation exists in the form component but not in the API route, so it can be bypassed with a direct API call
- No Content Security Policy — Missing CSP headers allow injected scripts to execute freely
- Rich text editors without sanitization — WYSIWYG editors that save and display raw HTML from users
- URL parameters used directly — Query string values rendered on the page without escaping
How to Fix It
- Add server-side validation with Zod — Define strict schemas: const schema = z.object({ name: z.string().min(1).max(100), email: z.string().email() }); and validate every API input
- Never use dangerouslySetInnerHTML with user data — Replace it with regular JSX text rendering: {userComment} instead of dangerouslySetInnerHTML={{__html: userComment}}
- Install DOMPurify for HTML content — If you must render HTML, sanitize it: DOMPurify.sanitize(htmlContent, { ALLOWED_TAGS: ['p', 'b', 'i', 'a'] })
- Add Content-Security-Policy headers — Configure CSP to block inline scripts: Content-Security-Policy: default-src 'self'; script-src 'self'
- Validate on both client and server — Share Zod schemas between frontend forms and backend API routes for consistent validation
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Get HelpFrequently Asked Questions
What is the difference between validation and sanitization?
Validation checks that input meets your requirements (correct format, length, type) and rejects bad input. Sanitization modifies input to remove dangerous content while keeping the data. You should do both: validate first, then sanitize what passes.
Does React protect against XSS automatically?
React's JSX auto-escapes content in curly braces ({variable}), which prevents most XSS. However, using dangerouslySetInnerHTML, creating elements via DOM APIs, or setting href/src attributes with user data can still introduce XSS vulnerabilities.