Common security mistakes founders miss before launch

A demo passes when the happy path works for the person who built it. A launch is the opposite — strangers arrive, click in unexpected orders, change URLs, and probe what the UI hides. The gap between “it works for me” and “it survives strangers” is where almost every preventable incident lives.

None of the mistakes below are subtle. They get missed because they live in the parts of the app you never look at: server responses you do not normally see, defaults nobody changed, headers no one configured, routes that exist but are not in the navigation.

A login screen rendering does not prove the page behind it is protected. AI builders reliably produce the visible part — the form, the redirect on success, the welcome screen — but the backend check that decides who is actually allowed in is easy to leave half-done. Worse, the APIs behind the UI can still be callable directly by anyone.

What to check

• Open a dashboard or admin URL in a private window while logged out — it should redirect or block, not render.

• Try changing an ID in a URL or request to load another user's data — it should fail.

• Confirm admin actions are not callable by regular users, even when they know the endpoint.

For the full pass on this, see the authentication security checklist.

A quick definition: public exposure means information or files reachable without logging in. The most damaging incidents for small apps are rarely sophisticated — they are usually a config file anyone can download or a service key shipped to the browser. The bundle that runs your frontend is downloadable by every visitor, which means anything inside it is effectively public.

What to check

• Visit yourdomain.com/.env and /.git — both should return 404, not contents.

• Confirm service keys and private tokens are not in your frontend bundle.

• Disable production source maps unless you specifically need them.

• Remove debug or info endpoints that print environment values.

For the full walkthrough, see public .env files and exposed secrets.

Browser-facing protections are response headers that tell the browser how to handle your site more safely — enforcing HTTPS, refusing to be embedded by other sites, restricting where scripts can load from. They are cheap to add and meaningfully reduce the impact of common attacks, but they are easy to forget because the demo works without them.

What to check

• HTTPS is enforced and HTTP redirects to HTTPS.

• Framing protection is set so your app cannot be embedded elsewhere.

• A content policy restricts where scripts and content can load from.

• Content-type guessing is disabled.

For the practical reference, see the HTTP security headers checklist.

Modern hosting platforms give you HTTPS and a solid baseline, but they cannot configure your auth, your environment-variable scoping, or your database rules for you. Defaults that work for the demo can be wide open in production — a database table in test mode, a preview deployment that exposes real data, a CORS rule that allows every origin.

What to check

• Server-only secrets are not given a browser-exposed prefix in your platform settings.

• Preview and staging deployments do not expose real user data.

• Database security rules are not in open test mode.

• CORS is not set to allow all origins on credentialed endpoints.

If you host on Vercel, the Vercel security checklist covers the platform-specific items. If you use Supabase, the Supabase RLS checklist covers the database side.

Admin features concentrate risk. One unprotected admin route can expose every user's data at once, and impersonation or support tools left in production can let a regular user reach things they should not. These flows are often built last and reviewed least.

What to check

• Admin routes are not reachable by a regular logged-in user.

• Admin actions (delete, edit, export, impersonate) re-check the user's role server-side.

• Debug or impersonation tools are disabled or restricted in production.

• Support endpoints do not accept arbitrary user IDs without an extra check.

A polished homepage is the easiest part of a launch. It tells you nothing about the parts of the app that strangers will actually push on — your routes that are not in the navigation, your error responses, your API behavior. A homepage is a signal of effort; it is not a signal of safety.

What to check

• Trigger an error and confirm the response does not reveal stack traces or internal paths.

• Open routes that are not linked in the UI (admin, debug, internal) and confirm they are restricted.

• Check API responses for fields that should not ship to the client.

• Confirm only the intended production deployment and domain are public.

A focused pre-launch sweep takes an afternoon. Work through both pillars rather than inventing your own list — they are designed to cover the surface a stranger actually sees.

• Run the focused pre-launch pass.

• Run the broader nine-area review on top of it.

• Test as a second, low-privilege user — try to break your own access rules.

• Run a public scan and confirm the obvious gaps are closed.

• Re-scan after fixes to confirm each issue is actually resolved.

The pillars are the launch security checklist (the final pre-launch readiness pass) and the vibe coding security checklist (the broader review).

GuardMint runs a public, non-invasive scan of your live URL — the same surface any visitor sees. It is built to catch the categories of mistake above from the outside. Our methodology explains how the scan works.

• Exposed files like .env, .git, and source maps reachable on your domain.

• Secret-looking keys and tokens visible in your frontend bundle.

• Missing or misconfigured security headers and HTTPS issues.

• Overly permissive CORS and weak cookie flags.

• Error responses that leak internal details.

A scan sees what is publicly reachable. The items below depend on access rules, permissions, or code logic no external scan can confirm.

• Whether your authentication and authorization rules are actually correct.

• Whether per-user data access is enforced in the database, not just the UI.

• Whether admin and role-based access is checked on every sensitive action.

• Whether business logic — billing, sharing, exports — behaves safely.

What is the most common security mistake founders miss?

Assuming a working login screen means authentication is safe. A page can render a login form for anyone with the URL, and the API behind it can still be callable without authentication. Real protection comes from the server and database enforcing access, not from the visible UI.

Why do founders miss security issues before launch?

Because the app works in a demo, and demos do not exercise the parts that fail under real use: stranger access, malicious inputs, ID swapping, and edge cases. AI builders and fast workflows amplify this — code ships faster than it gets reviewed.

Are these mistakes specific to vibe-coded apps?

They show up most in vibe-coded apps because those workflows skip review steps a more traditional team would have, but the mistakes themselves are universal. The same patterns appear in hand-written apps that ship in a hurry.

Can a scan catch all of these mistakes?

A public scan catches what is visible from the outside: exposed files, missing headers, leaky errors, secret-looking keys in the bundle. It cannot confirm access rules, admin role checks, or business logic. Pair the scan with manual checks using a second test account.

Which of these mistakes is the most dangerous?

Whichever one leaks user data first. In practice the two with the highest blast radius are exposed service keys and database rules that allow public reads — both can expose every user's data at once.

How long does it take to fix these?

Most are configuration changes you can make in a dashboard, not rewrites. A focused founder can typically close the obvious gaps in a single afternoon, then re-scan to confirm.