v0 App Security: What's Missing by Default

Quick answer: v0 app security has one failure mode the rest of this series doesn't: a secret key accidentally prefixed NEXT_PUBLIC_, which ships straight into the browser bundle for anyone to read. No exploit required, just a naming convention nobody flagged. Past that one risk, v0 apps carry the same unset checklist as everything else built fast: headers, DNS records, and authorization checks that look fine until someone checks them on purpose.

Jump to: what makes v0 different from Lovable, Bolt, and Cursor, the checklist v0 never runs for you, how it compares to the rest of this series, why this pattern isn't hypothetical, how to fix it in an afternoon (with the actual code), and a quick FAQ at the end.

v0 is closer to Cursor than it looks

Everything else in this series (Lovable, Bolt.new) generally bundles a database and a host in the same product, which is why Row-Level Security keeps showing up as the headline finding. v0, built by Vercel, started life as a UI generator: describe a component or a page, get back clean React and Tailwind code, often built on shadcn/ui. It's grown into something that can scaffold fuller apps, API routes, server actions, integrations with Postgres providers like Neon and Supabase, but the center of gravity is still closer to Cursor's than to Lovable's: v0 generates code you deploy, usually to Vercel, rather than a platform quietly managing a database's access policies underneath you.

That distinction matters because it changes where the risk actually sits. There's no RLS-shaped gap waiting by default the way there is with a Supabase-backed Lovable or Bolt app, unless you've specifically wired one up yourself, in which case the same RLS advice from the Lovable post applies just as directly. What v0 has instead is a gap that comes from its own ecosystem: Next.js's environment variable convention, and how easy it is to get the client/server boundary wrong once an AI is filling in the blanks for you.

Deploying to Vercel does get you real things for free. HTTPS and certificate management are handled by Vercel's edge network without anyone touching a config file, which is more than Bolt's export path or a bare Cursor deployment gets by default. That's genuinely worth crediting. It's also why the rest of this list is easy to assume is handled too, when most of it isn't.

The checklist v0 never runs for you

A secret shipped to the browser via NEXT_PUBLIC_. This is the one to check first, and it's specific to how Next.js handles environment variables. Anything prefixed NEXT_PUBLIC_ gets bundled into client-side JavaScript by design, that's the whole point of the prefix, it's meant for values that are safe to expose, like a public API endpoint or an analytics ID. The failure mode is an AI-assisted prompt-and-fix loop reaching for that prefix on a server-side secret, a database connection string, a service-role key, a payment provider's secret key, because it's the fastest way to make a "variable not defined" error go away. The moment that happens, the key is sitting in plain text in a bundle any visitor's browser downloads. No exploit needed, no misconfigured header, just a naming convention that quietly did exactly what it was designed to do, to the wrong variable.

Security headers. The response headers that stop a malicious script from running loose in a visitor's browser (Content-Security-Policy), force every connection onto HTTPS (Strict-Transport-Security), or stop your site being loaded invisibly inside someone else's page (X-Frame-Options). Vercel doesn't add these by default just because your app is hosted there, they're set through a next.config.js headers block or Vercel-specific config, the same manual step every other tool in this series requires.

Authorization on API routes and server actions, not just authentication. v0 will generate a Next.js API route or a server action that checks whether a request comes from a logged-in session without much trouble. Whether it also checks that the logged-in user is allowed to see the specific record being requested, not just any record with a valid session, is a separate question that depends on how the prompt was framed, the same gap the Cursor post walked through.

DNS and email authentication. DMARC and SPF let mail servers verify that an email claiming to be from your domain actually is; CAA controls which certificate authorities can issue a certificate for it. All three live at your domain registrar, not inside Vercel, and Vercel hosting your app doesn't touch them. Point a custom domain at a v0-built app, which is the normal path once you're past the prototype stage, and the domain is spoofable until someone adds these records directly.

CORS policy on any API surface. CORS decides which other websites are allowed to call your API directly from a visitor's browser. A wide-open origin is normal while iterating on your own routes. It's also what ships to production if nobody circles back to scope it, particularly once credentialed requests enter the picture.

Cookie flags and session handling. The settings that stop a session cookie from being read by an injected script (HttpOnly), sent over an unencrypted connection (Secure), or replayed from another site (SameSite), plus whether it actually expires. v0-generated auth (often via NextAuth, Clerk, or a custom flow) will work for the case that got tested. Whether the session is hardened against fixation or cookie theft depends on whether someone thought to check, not on whether the login screen looks right.

Exposed configuration and verbose errors. A misconfigured API route that returns a full stack trace on failure, a dependency tree nobody's scanned for known CVEs, these are hygiene decisions, not something v0 or Vercel enforces on your behalf just because the deploy succeeded.

None of these are exotic, and none of them are v0-specific failures, they're the same categories that show up everywhere in this series. The NEXT_PUBLIC_ one is the exception worth remembering by name, because it's the one failure mode on this whole list that requires zero attacker skill at all, just a browser's "view source."

How v0 compares to the rest of this series

Every tool in this series leaves the same rough shape of gap, but the specific default that trips people up first is different for each one:

v0 is the odd one out on this table in a good way: no bundled database means no default RLS-shaped gap. The tradeoff is a risk none of the others really have, one that lives entirely in how Next.js handles environment variables.

This isn't hypothetical, we've seen the pattern

The first three posts in this series each found the same core cluster on a real, live app: missing headers, missing DNS hardening, authorization checks that looked fine from the UI and weren't. The vibe-coding post found it next to a perfect 100 on performance. The Cursor post found the same authorization gap in a tool with no hosting layer at all. The Bolt.new post found it sitting next to an unset Supabase policy, catalogued elsewhere as CVE-2025-48757. The pattern isn't about any one tool. It's what happens whenever the thing being optimized for is "does this satisfy the prompt," and a security control doesn't stop the prompt from being satisfied.

The NEXT_PUBLIC_ failure specifically isn't a hypothetical either, it's one of the most commonly flagged misconfigurations across Next.js projects generally, AI-assisted or not, precisely because the convention is easy to reach for under pressure and gives no warning when it's wrong. The broader research backs up why AI-assisted code specifically keeps landing here: Veracode's 2025 GenAI Code Security Report tested over 100 large language models across 80 coding tasks and found AI-generated code introduced exploitable flaws in 45% of tests, with no improvement as models got better at writing functional code. A 2023 Stanford study (Perry et al., ACM CCS) found developers using an AI coding assistant wrote measurably less secure code than developers without one, and felt more confident about it, not less. The pattern doesn't need a platform-specific database gap to show up, a fast-moving prompt loop and a permissive-by-design naming convention is enough on its own.

Fixing it is an afternoon, not a rebuild

Finding a leaked NEXT_PUBLIC_ secret means rotating the key immediately, not just renaming the variable, since anything already shipped in a bundle has to be treated as compromised:

# Wrong - this ships straight into every visitor's browser bundle
NEXT_PUBLIC_SUPABASE_SERVICE_ROLE_KEY=eyJhbGciOiJIUzI1NiIs...

# Right - server-only, never bundled client-side, read only in
# API routes, server actions, or server components
SUPABASE_SERVICE_ROLE_KEY=eyJhbGciOiJIUzI1NiIs...

Headers are a next.config.js block:

// next.config.js
module.exports = {
  async headers() {
    return [
      {
        source: '/:path*',
        headers: [
          { key: 'Content-Security-Policy', value: "default-src 'self'" },
          { key: 'Strict-Transport-Security', value: 'max-age=63072000; includeSubDomains; preload' },
          { key: 'X-Frame-Options', value: 'DENY' },
          { key: 'Referrer-Policy', value: 'strict-origin-when-cross-origin' },
        ],
      },
    ]
  },
}

DNS records are a registrar dashboard, CORS is a policy change, cookie flags are a few lines in your auth setup. None of it touches the component code v0 generated for you, which is why it's worth an afternoon before the link goes out.

This is the same gap FlawPilot's free scan is built to catch, across security, performance, infrastructure, and SEO. Every finding lands in a "What to do next" list ranked by what actually matters, with the fix for the top issue in every area spelled out in plain English, free, no CVSS score to decode. Drop in your URL, no login, no repo access, and in about two minutes you know exactly which of the six items above still needs attention, including whether anything in your client bundle looks like a secret that shouldn't be there.

How FlawPilot helps

FlawPilot is useful because it connects detection to remediation. A scan can tell you a Row-Level Security policy is missing. The next step, actually closing it, is what determines whether the risk goes away.

Every finding lands in a ranked "What to do next" list, written in plain English instead of a severity label. The fix for the top issue in every pillar, security, performance, infrastructure, SEO, is included in the free report, spelled out clearly enough to act on without a security background. For a full crawl of the site, and for findings that go deeper than a config change, Logicwind's engineering team builds a prioritized remediation roadmap and puts people on it directly: RLS policies, header configuration, DNS records, all of it.

The boundaries matter as much as the capability. FlawPilot only checks publicly accessible signals to run the scan, it never touches your server, your codebase, or your credentials, and it doesn't auto-apply any fix without a human in the loop. Finding the gap and fixing the gap happen through the same team, but that means engineers doing the work, not a bot merging code on your behalf.

This is the fifth post in our series on what AI coding tools leave unconfigured by default. The first one walked through a real scan end to end. The second one covered Cursor. The third one covered Lovable. The fourth one covered Bolt.new. This one's about v0, and the pattern holds: the code works, the security step just isn't anyone's job until you make it someone's job.

The FlawPilot team, Logicwind