SCAN YOUR V0.DEV APP FOR VULNERABILITIES

v0 generates Next.js components with shadcn/ui primitives, deployed to Vercel in a click. The output is UI-first — which is exactly why v0 apps get skipped in security reviews. “It’s only frontend” is the trap: the generated code decides what ships to every visitor’s browser, and the moment you wire a component to a real backend, the placeholder auth, client-side validation, and demo API keys that made the preview work become the production attack surface.

The failure modes are specific to the Next.js boundary. Env vars prefixed NEXT_PUBLIC_ inline into the client bundle. Server actions compile to public HTTP endpoints whether or not a form sits in front of them. app/api/ route handlers ship without a session check because the chat session never needed one. None of this is visible in the v0 preview — it only shows up when someone attacks the deployed app.

That is what VibeEval does: a black-box scan of your deployed v0 app that attacks it the way a stranger with DevTools and curl would, before your users do.

Common vulnerabilities we find in V0.dev apps

The recurring shapes in v0-generated Next.js apps, and how each one gets exploited.

Placeholder auth that ships to production

v0 scaffolds components with mock authentication — useUser() hooks returning { id: 'demo-user-1' }, hardcoded JWTs, “TODO: replace with real session” comments. Wire those components to a real database without replacing the auth layer and every request runs as the same demo user; your entire customer base shares one record. The exploit is trivial: there is nothing to bypass, because nothing checks identity. Fix direction: replace the placeholder with a real provider (NextAuth, Clerk, Supabase Auth) and confirm auth() returns the actual signed-in user before any write.

Secrets in the client bundle via NEXT_PUBLIC_

To make examples self-contained, v0 leans on NEXT_PUBLIC_ env vars — and Next.js inlines every one of them into the JavaScript served to all visitors. A Stripe or OpenAI key that ever carried the prefix is public. The exploit: open the deployed _next/static/ chunks and grep for sk_live, sk-proj-, re_ — bots do this within hours of deploy. Fix direction: move every privileged call to a route handler or server action reading an unprefixed env var, and rotate anything that ever shipped in a bundle. The Token Leak Checker automates the bundle check.

XSS via dangerouslySetInnerHTML

Asked to render rich text or markdown, v0 reaches for the one-line React API:

<div dangerouslySetInnerHTML={{ __html: post.body }} />

If post.body is user-provided — a comment, a bio, LLM output — an attacker stores a script payload and it executes in every viewer’s session. This is the same surface as LLM-rendered HTML and Markdown. Fix direction: sanitize with DOMPurify before rendering, or use react-markdown with the default safe renderer.

Server actions without validation (mass assignment)

v0 forms validate with Zod on the client, then the server action trusts the body and spreads it into a database update. Drop the client validation in DevTools and submit { "isAdmin": true } — if the action does db.users.update(formData), you just promoted yourself. This is textbook mass assignment. Fix direction: parse the input through a server-side schema as the first line of every action, with an explicit field allowlist.

Unauthenticated API routes and BOLA

Generated app/api/*/route.ts handlers routinely ship without a session check — the page in front is gated by middleware, but the JSON behind it answers anyone with curl. And when auth exists, ownership often doesn’t: sign in as user B, replay user A’s request with A’s record ID, and the handler returns A’s data. That two-account replay is the highest-yield test in AI-generated CRUD — see BOLA in AI-generated CRUD. Fix direction: resolve the session at the top of every handler and scope every query to the session user.

Source maps and preview URLs in production

Production source maps hand attackers your unminified TypeScript, comments and TODOs included — verify /_next/static/chunks/*.js.map returns 404, and see source maps and exposed .git. Separately, every Vercel push gets a <branch>-<hash>.vercel.app URL; if your auth gate lives on the custom domain only, the preview URL bypasses it. Fix direction: keep productionBrowserSourceMaps off and enable Vercel Deployment Protection or reject non-production hosts in middleware.

How VibeEval works with V0.dev

1. Enter your deployed URL. Point VibeEval at the Vercel deployment (production or a preview URL) — no code access, no agent install, exactly what an attacker sees.
2. The agent attacks the app in a real browser. It maps pages, app/api/ routes, and server-action endpoints, then probes them: requests with the session stripped, two-account BOLA replays, mass-assignment payloads against form actions, bundle checks for key prefixes and NEXT_PUBLIC_ leaks, security-header and source-map checks.
3. Read the report, paste the fixes. Findings arrive ranked by severity with the exact route or action affected — and each ships with a paste-ready fix prompt you can drop straight into the v0 chat to regenerate the component securely.

Manual testing vs VibeEval

The honest framing: you still want a human reading diffs for logic. The scanner wins on repeatability — v0’s whole appeal is regenerating fast, and every regeneration deserves the same security pass without the same hours.

Frequently asked questions

Does VibeEval scan v0 component code directly?

VibeEval scans the deployed application — the integrated surface where components meet real auth, real data, and real APIs. A component that is harmless in the v0 preview becomes a finding once it is wired to your backend, and only a deployed-app scan sees that. For component-level checks during development, use the MCP integration.

What if I only use v0 for UI and have a separate backend?

Scan anyway. The scanner tests the whole deployed app, backend included, and the frontend v0 generated is not inert: it decides what ships in the bundle (keys, source maps), what renders unsanitized, and which endpoints your forms call with what payloads. Findings are reported per surface, so v0-originated issues are easy to isolate.

Can v0 components really introduce security issues if they’re “just frontend”?

Yes — that assumption is the most common way v0 apps ship vulnerable. The bundle can carry secrets, dangerouslySetInnerHTML can carry XSS, client-side route guards gate nothing, and the server actions v0 generates alongside the UI are public HTTP endpoints. Frontend-first does not mean attack-surface-free.

How do I secure a v0 + Vercel deployment?

Four moves cover most of it: replace placeholder auth with a real provider, keep every secret out of NEXT_PUBLIC_ and client components, add a session check plus server-side validation to every route handler and action, and set security headers in next.config.js. Then scan the deployed URL to verify — the guide walks through each step.

Should I re-scan after every v0 regeneration?

Yes. v0 can rewrite security-critical code when you ask for an unrelated change — a regenerated component can restore a NEXT_PUBLIC_ var, drop an auth check, or re-add a debug route. A scan after each significant regeneration catches the regression before users do.

Related V0.dev resources

• How to Secure v0.dev — the step-by-step hardening checklist: route-handler auth, NEXT_PUBLIC_ audit, source maps, headers.
• Is Vercel v0 Safe? — in-depth analysis of v0’s defaults and the four integration risks that matter most.
• v0 Security Checklist — severity-ordered pre-launch checklist, including the after-every-regeneration diff routine.
• Token Leak Checker — free check for API keys exposed in your deployed bundle.
• BOLA in AI-generated CRUD — the cross-user access pattern behind the most serious v0 findings.

Test your V0.dev app before launch

The v0 preview shows you what the app looks like; it cannot show you what the app leaks. Run a scan against your deployed URL, fix the findings with the generated prompts, and ship the version that holds up when someone hostile opens DevTools.