React Security

Priority: P0 (CRITICAL)

Preventing vulnerabilities in client-side apps.

Implementation Guidelines

• XSS: Avoid dangerouslySetInnerHTML. Sanitize via DOMPurify if needed.
• URLs: Validate javascript: protocols in user links.
• Auth: Store tokens in HttpOnly cookies. Avoid localStorage.
• Deps: Run npm audit. Pin versions.
• Secrets: Server-side only. No .env secrets in build.
• CSP: Strict Content-Security-Policy headers.

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.

Code

import DOMPurify from 'dompurify';

// Safe HTML Injection
function SafeHtml({ content }) {
  const clean = DOMPurify.sanitize(content);
  return <div dangerouslySetInnerHTML={{ __html: clean }} />;
}

// Bad Link Prevention
const safeUrl = url.startsWith('javascript:') ? '#' : url;
<a href={safeUrl}>Link</a>;