Top 12 Security Risks in Vibe-Coded Apps Built with Replit Agent 3

Understanding Security Risks in AI-Assisted Development (Using Replit Agent 3)

“Vibe Coding” has changed how we build software—developers describe what they want in plain English, and AI agents like Replit Agent 3 generate the scaffolding. It’s fast, magical… and dangerously easy to forget the fundamentals of secure software engineering.

In October 2025, my team conducted a comprehensive security audit of a typical “vibe-coded” full-stack app built with Replit Agent 3. We uncovered 12 vulnerabilities, ranging from critical to low severity.
This post breaks down what each issue means, why it happens in AI-generated code, and how to fix it.

🔴 Critical Issues (Urgent Action Required)

1. Unauthenticated Blog Management Endpoints

Impact: Anyone could create, edit, or delete blog posts—no login required.

Why it happens:
AI agents often generate route handlers for CRUD operations without enforcing authentication. If the model sees examples of app.post('/api/blog', ...), it happily scaffolds the same—minus any security middleware—unless prompted explicitly.

Real-world exploit:
Attackers can POST malicious content, delete your data, or deface your blog.

Fix:
Add authentication middleware:

app.use('/api/blog', requireAuth, blogRoutes);

And protect admin-only routes separately.

Takeaway:
AI writes functionally correct code, not context-aware code. Always review generated routes for authorization gaps.

2. Weak Stripe Webhook Signature Verification

Impact: Attackers could forge “payment successful” events, unlocking paid content without paying.

Why it happens:
Replit Agent 3 frequently scaffolds payment integrations but omits secure verification of webhook signatures.

Real-world exploit:
A malicious actor could send a fake webhook payload claiming a successful charge. The server trusts it, grants access, and you lose revenue.

Fix:

const event = stripe.webhooks.constructEvent( req.rawBody, req.headers['stripe-signature'], process.env.STRIPE_WEBHOOK_SECRET );

Reject any webhook that fails verification.

Takeaway:
Never trust incoming webhook data—verify signatures or don’t process.

3. Race Condition in Course Enrollment

Impact: Two users can “simultaneously” buy the last seat in a class.

Why it happens:
AI code generation rarely considers concurrency. Without database-level locks or transactions, two enrollment requests can succeed before stock is decremented.

Fix:
Use transactions with row-level locking:

BEGIN; SELECT * FROM seats WHERE course_id=123 FOR UPDATE; -- check & update COMMIT;

Takeaway:
Race conditions are invisible until your system scales. Guard critical sections using transactions, queues, or atomic operations.

🔶 High-Severity Issues

4. XSS via dangerouslySetInnerHTML

Impact: A malicious user could inject JavaScript into your site.

Why it happens:
Replit’s front-end code often uses dangerouslySetInnerHTML to render blog content or user input directly. When unescaped, that becomes a script-injection gateway.

Fix:
Sanitize user content with libraries like DOMPurify or render Markdown safely.

Takeaway:
Never trust any HTML coming from users—sanitize it or render text only.

5. Missing Route Parameter Validation

Impact: Attackers can send malformed parameters like /api/course?programType=<script> to cause unexpected behavior or denial of service.

Why it happens:
AI code generation usually treats request parameters as harmless strings.

Fix:
Use schema validation:

import { z } from 'zod'; const schema = z.object({ programType: z.enum(['basic', 'advanced']), level: z.number().min(1).max(10), });

Takeaway:
Every route parameter and request body needs validation before it touches your database.

6. Client-Side API Key Storage

Impact: Exposed Firecrawl API key found in localStorage.

Why it happens:
Replit agents sometimes generate code that stores keys or tokens in the client for convenience.

Fix:
Move all secrets to environment variables and proxy calls through the server.

Takeaway:
No API key belongs in the browser. Ever.

🟡 Medium-Severity Issues

7. No Rate Limiting (DoS Vulnerability)

Without throttling, a malicious script could hammer your API until your server collapses.

Fix:
Use express-rate-limit:

app.use(rateLimit({ windowMs: 60_000, max: 100 }));

8. Missing CORS Configuration

Default permissive CORS (app.use(cors())) allows any domain to make requests—potentially enabling Cross-Site Request Forgery (CSRF) or data theft.

Fix:
Restrict origins:

app.use(cors({ origin: 'https://yourapp.com' }));

9. Missing Security Headers (Helmet.js)

Impact: Increases exposure to XSS, clickjacking, and sniffing attacks.

Fix:
Add Helmet:

import helmet from 'helmet'; app.use(helmet());

This sets headers like X-Frame-Options and Strict-Transport-Security.

10. No Session Management

Without session tracking, user authentication (if later added) will be stateless and vulnerable to replay attacks.

Fix:
Use secure cookies or JWTs with expiration and rotation.

🟢 Low-Severity Issues

11. Excessive Error Information Disclosure

AI-generated code often logs full stack traces or database errors to the console or client.

Risk:
Attackers can infer database structure or file paths.

Fix:
Use generic error responses:

res.status(500).json({ error: 'Internal server error' });

12. No CSRF Protection

If you implement sessions or cookies later, you’ll need CSRF tokens to prevent cross-origin form submissions.

Fix:
Use csurf middleware in Express.

✅ SQL Injection Status

Good news—Replit Agent 3 uses Drizzle ORM, which safely parameterizes queries.
Always confirm that raw SQL queries aren’t introduced later.

🧩 Why These Issues Are Common in Vibe Coding

Root Cause Description Preventive Action AI prioritizes functionality Agents optimize for “working code,” not “secure code.” Always run a security lint + audit. Lack of human review Developers assume the AI “knows best.” Treat AI output as a junior dev’s code. Review line-by-line. Inconsistent prompt discipline Unclear prompts lead to missing auth, validation, etc. Include security context in every prompt (“with authentication, input validation, helmet, rate limiting”). Fast iteration cycles Vibe coding skips QA/security phases. Schedule security checkpoints after every major generation cycle.

🧠 Final Thoughts

Replit Agent 3 and vibe coding let creators ship ideas in hours—but speed without guardrails equals exposure.
Security isn’t optional or retrofittable; it must be prompted, reviewed, and enforced at every layer.

🧩 Checklist for Vibe Coders

• ✅ Add helmet.js and rate limiting

• ✅ Validate all inputs (Zod/Yup)

• ✅ Use auth middleware on sensitive routes

• ✅ Never expose secrets client-side

• ✅ Verify webhook signatures

• ✅ Log safely and handle errors gracefully

Building with AI means you’re moving fast—just make sure you’re not moving fast toward a breach.

Keywords: vibe coding security, Replit Agent 3 vulnerabilities, AI code security 2025, helmet.js, webhook verification, AI app security audit