React Security

Priority: P0 (CRITICAL)

Preventing vulnerabilities in client-side apps.

Implementation Guidelines

• XSS Prevention: Never use

  dangerouslySetInnerHTML

  without sanitization. Use

  DOMPurify.sanitize(input)

  for all user-provided HTML. Avoid

  javascript:

  protocols in

  href

  or

  src

  .
• Authentication: Store JWT/Sessions in

  HttpOnly

  and

  Secure

  cookies to prevent theft via XSS. Never store secrets in

  localStorage

  or in the built JS bundle.
• Data Flow: Escape all serialized state if injecting into the HTML (e.g., in SSR). Use a Content Security Policy (CSP) to restrict script sources and prevent inline execution.
• CSRF Protection: Use CSRF tokens for state-changing requests (PUT/POST/DELETE). Implement SameSite=Strict cookies where applicable.
• Input Sanitization: Always validate and sanitize user inputs on the backend. Frontend validation is for UX only.
• Dependency Management: Run

  npm audit

  /

  pnpm audit

  regularly. Pin specific dependency versions and use

  npm-check-updates

  .
• Security Headers: Ensure the server sends

  X-Frame-Options: DENY

  ,

  X-Content-Type-Options: nosniff

  , and

  Permissions-Policy

  .

Anti-Patterns

• No

  eval()

  : RCE risk.
• No Serialized State: Don't inject JSON into DOM without escaping.
• No Client Logic for Permissions: Backend must validate.

References

See references/REFERENCE.md for DOMPurify usage, CSP headers, OAuth2/JWT auth patterns, and CSRF protection.