How to Fix Missing Input Validation in Vibe-Coded Forms

Quick answer

Missing input validation is one of the most common security flaws in vibe-coded apps. AI-generated forms often lack server-side checks, leaving you vulnerable to injection attacks and data corruption. To fix it, add validation logic on both client and server, sanitize inputs, and use a security scanner to catch gaps before deployment.

What to check first

Before diving into code, run through this checklist to assess your current state:

Step-by-step fix

1. Add server-side validation

AI tools often generate forms with only client-side validation. That's easy to bypass. Here's how to add server-side checks using a Node.js + Express example with the express-validator library:

const { body, validationResult } = require('express-validator');

app.post('/signup',
  [
    body('email').isEmail().normalizeEmail(),
    body('password').isLength({ min: 8 }),
    body('age').isInt({ min: 0, max: 120 })
  ],
  (req, res) => {
    const errors = validationResult(req);
    if (!errors.isEmpty()) {
      return res.status(400).json({ errors: errors.array() });
    }
    // proceed with sanitized input
  }
);

2. Sanitize inputs to prevent injection

Use a library like DOMPurify for HTML or validator for general sanitization:

const sanitizeHtml = require('sanitize-html');
const cleanInput = sanitizeHtml(req.body.comment, {
  allowedTags: [],
  allowedAttributes: {}
});

3. Validate file uploads

Never trust file extensions. Check MIME type and content:

const fileFilter = (req, file, cb) => {
  if (file.mimetype === 'image/png' || file.mimetype === 'image/jpeg') {
    cb(null, true);
  } else {
    cb(new Error('Only PNG and JPEG allowed'), false);
  }
};

4. Use a validation schema for APIs

For REST or GraphQL, define a schema (e.g., with Joi or Zod):

const Joi = require('joi');
const schema = Joi.object({
  username: Joi.string().alphanum().min(3).max(30).required(),
  email: Joi.string().email().required()
});
const { error, value } = schema.validate(req.body);

5. Automate scanning

After implementing fixes, run your app through a security headers checker and a secret leak scanner to ensure no other gaps remain. For continuous protection, consider continuous security monitoring.

Common mistakes

Vibe-coded apps often make these errors:

FAQ

What happens if I don't validate inputs?

Attackers can inject SQL, XSS, or shell commands into your app. This can lead to data theft, account takeover, or remote code execution.

Is client-side validation enough?

No. Client-side validation is only for user experience. Attackers bypass it by disabling JavaScript or sending direct HTTP requests.

What's the easiest way to start fixing validation?

Install a validation library like express-validator (Node.js) or Joi, then add server-side checks to every endpoint that accepts user input. Run a free AI app security scanner to find missing validations.

---

Missing input validation is a silent killer in vibe-coded apps. By following this guide, you can harden your forms and protect your users. For a full audit, scan your app with OverMCP – it's built for AI-generated code.