How to secure an app built with AI coding tools

Why AI-generated apps fail differently

Vibe-coded apps can be secure. They need an extra audit pass because the failure modes are structural, not careless:

• Assistants inline hardcoded keys. You ask for a fix to an auth error and get a pasted Supabase example that assumes a service-role client. The key ends up at the top of a page component. Both the anon client and the service client coexist; both ship.
• Generated servers default to permissive CORS. Generated Express / Fastify handlers often ship with cors({ origin: '*' }) because that's the fastest way to get a working preview. The middleware never gets a second pass.
• Rules files get skipped. Firestore-backed projects generate the data model but rarely touch firestore.rules. Test-mode rules let anyone read and overwrite data until someone replaces them.
• RLS never enters the migration. A generated Supabase schema and CRUD surface use the anon key, but ENABLE ROW LEVEL SECURITY never enters the migration. Anonymous users can read or write any row.
• Handlers trust IDs. A generated GET /api/items/[id] reads the param and queries Postgres without verifying ownership. Active scans on a verified domain test for this (IDOR / BOLA).

The immediate audit: grep your codebase for risk patterns

Before you harden anything, find what's already broken. These greps each take under a minute:

grep -RIn 'NEXT_PUBLIC_SUPABASE_SERVICE' src/
grep -RIn 'sk_live_\|pk_live_\|STRIPE_SECRET' src/
grep -RIn 'sk-ant-\|^sk-' src/  # Anthropic / OpenAI
grep -RIn 'AIza\|AKIA' src/        # Google / AWS
grep -RIn 'eyJh[A-Za-z0-9_-]\{20,\}' src/  # JWT-shaped strings

# Supabase migrations
grep -RIn 'CREATE TABLE public\.' supabase/migrations/
grep -RIn 'ENABLE ROW LEVEL SECURITY\|FORCE ROW LEVEL SECURITY' supabase/migrations/

# Firebase / Firestore
cat firestore.rules  # confirm no `if true;` matches

grep -RIn 'getSession()' src/   # should be getUser() server-side
grep -RIn 'localStorage\.\(set\|get\)Item.*token' src/
grep -RIn 'jwt.verify.*\(noVerify\|skipVerify\)' src/

# Confirm middleware location for src/ layouts
ls src/middleware.ts middleware.ts 2>&1

# Look for CSP and security headers
grep -RIn 'Content-Security-Policy\|Strict-Transport-Security' src/

Hardening at deploy time

Once source is clean, lock down how the app reaches production.

// src/middleware.ts
import { NextResponse, type NextRequest } from 'next/server';

export function middleware(request: NextRequest) {
  const nonce = crypto.randomUUID().replace(/-/g, '');
  const csp = [
    `script-src 'nonce-${nonce}' 'strict-dynamic'`,
    `style-src 'self' 'unsafe-inline'`,
    `img-src 'self' data: https:`,
    `connect-src 'self' https://*.supabase.co`,
    `object-src 'none'`,
    `base-uri 'self'`,
    `frame-ancestors 'none'`,
  ].join('; ');

  const requestHeaders = new Headers(request.headers);
  requestHeaders.set('x-nonce', nonce);

  const response = NextResponse.next({ request: { headers: requestHeaders } });
  response.headers.set('Content-Security-Policy', csp);
  response.headers.set('X-Content-Type-Options', 'nosniff');
  response.headers.set('Strict-Transport-Security', 'max-age=31536000; includeSubDomains');
  return response;
}

export const config = {
  matcher: ['/((?!_next/static|_next/image|favicon.ico).*)'],
};

-- supabase/migrations/XXXX_rls.sql
alter table public.profiles enable row level security;
alter table public.profiles force row level security;

create policy "profiles: read own"
  on public.profiles for select
  using (auth.uid() = id);

create policy "profiles: update own"
  on public.profiles for update
  using (auth.uid() = id)
  with check (auth.uid() = id);

// src/app/api/items/route.ts
import { NextResponse, type NextRequest } from 'next/server';
import { createClient } from '@/lib/supabase/server';

export async function POST(request: NextRequest) {
  const supabase = await createClient();
  const { data: { user } } = await supabase.auth.getUser();
  if (!user) return NextResponse.json({ error: 'unauthorized' }, { status: 401 });

  const body = await request.json();
  const { data, error } = await supabase
    .from('items')
    .insert({ ...body, user_id: user.id })  // server-supplied, not from body
    .select()
    .single();

  if (error) return NextResponse.json({ error: error.message }, { status: 400 });
  return NextResponse.json(data);
}

// src/app/api/posthog/[...path]/route.ts
import { type NextRequest } from 'next/server';

const UPSTREAM = 'https://us.i.posthog.com';

export async function POST(req: NextRequest, { params }: { params: Promise<{ path: string[] }> }) {
  const { path } = await params;
  const url = `${UPSTREAM}/${path.join('/')}`;
  return fetch(url, {
    method: 'POST',
    headers: { 'content-type': req.headers.get('content-type') ?? 'application/json' },
    body: await req.text(),
  });
}

function safeNext(raw: string | null): string {
  if (!raw) return '/dashboard';
  if (!raw.startsWith('/') || raw.startsWith('//')) return '/dashboard';
  return raw;
}

Ongoing: monitoring and re-scanning

Drift happens on every deploy. Treat security as a loop, not a checklist you finish.

# Or from CI, via the REST API:
curl -X POST https://fixvibe.app/api/v1/scans \
  -H "authorization: Bearer $FIXVIBE_TOKEN" \
  -H "content-type: application/json" \
  -d '{"target":"https://your-app.com"}'

Real failure patterns and their fixes

Five common patterns in AI-generated apps, each with the actual fix:

1. Service-role key in a client component

   Symptom: FixVibe reports an exposed Supabase service-role key on the production URL. Cause: an autocomplete pasted createClient(URL, SERVICE_ROLE_KEY) into a React component. Fix: move the service client to src/lib/supabase/service.ts with import 'server-only' at the top; create a parallel src/lib/supabase/client.ts using the anon key for client-side use; rotate the service-role key via Supabase Studio.

2. Firestore rules left in test mode

   Symptom: a high-severity open Firebase rules finding. Cause: generated rules read allow read, write: if request.time < timestamp.date(2026, 6, 1); — a time-bounded "allow all". Fix: scope each rule to the authenticated user — match /users/{userId}/posts/{postId} { allow read, write: if request.auth.uid == userId; } — and re-deploy firebase deploy --only firestore:rules.

3. Permissive CORS surviving into production

   Symptom: a high-severity CORS misconfiguration finding. Cause: generated Express middleware: app.use(cors({ origin: '*' })). Fix: allowlist your frontend origin: app.use(cors({ origin: ['https://your-app.com'], credentials: true })). For Next.js API routes, set Access-Control-Allow-Origin explicitly in the response.

4. RLS enabled but not forced

   Symptom: FixVibe reports that anonymous visitors can read a public table even though RLS looks enabled in the dashboard. Cause: RLS is on, but a policy such as USING (true) lets the anon role through, or the migration that tightened it never ran in production. Fix: replace the permissive policy with one scoped to auth.uid(), apply the migration, and re-scan.

5. Unsigned IDOR-walkable IDs

   Symptom: an active scan on your verified domain reports that one user can read another user's records at /api/items/1, /api/items/2, ... Cause: the API handler trusts the path param and queries Postgres without an ownership predicate. Fix: add .eq('user_id', user.id) on every read query, or move to signed URLs / UUIDs scoped under /api/users/[uid]/items/[id].

The vibe-code security loop

The goal isn't perfect security; it's eliminating the low-hanging fruit AI tools consistently miss so you can keep shipping fast.

1. Generate fast — use Cursor, Claude Code, Lovable, Bolt. That's the point.
2. Audit immediately — run the grep set above, check RLS, verify CSP, review auth boundary.
3. Harden at deploy — middleware, environment separation, CSP nonce, HSTS, server-only auth verification.
4. Monitor — FixVibe passive daily, active weekly on a verified domain, webhooks to Slack, threat detection on Unlimited.
5. Fix fast — use FixVibe coding-agent prompts for code/config findings and operator steps for DNS, provider, secret-rotation, or manual-review findings. Re-deploy, re-scan, close the loop.

Next steps

For the conceptual backdrop on DAST vs SAST and why AI-generated apps need their own scanning, read AI-generated code security scanning. For a quick-reference pre-ship audit, see the vibe coding security checklist.