Vercel Security Basics

Overview

Secure Vercel deployments with proper secret management, security headers, deployment protection, and access token hygiene. Covers environment variable scoping, Content Security Policy, and preventing common secret exposure patterns.

Prerequisites

• Vercel CLI installed and authenticated
• Access to Vercel dashboard
• Understanding of HTTP security headers

Instructions

Step 1: Secret Management with Environment Variables

# Add secrets scoped to specific environments
vercel env add DATABASE_URL production
vercel env add DATABASE_URL preview
vercel env add DATABASE_URL development

# Use 'sensitive' type — values hidden in dashboard and logs
vercel env add API_SECRET production --sensitive

# Via REST API
curl -X POST "https://api.vercel.com/v9/projects/my-app/env" \
  -H "Authorization: Bearer $VERCEL_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "key": "API_SECRET",
    "value": "sk-secret-value",
    "type": "sensitive",
    "target": ["production"]
  }'

Critical rule: Never prefix secrets with NEXT_PUBLIC_. Variables starting with NEXT_PUBLIC_ are inlined into the client JavaScript bundle and visible to anyone.

Step 2: Security Headers via vercel.json

{
  "headers": [
    {
      "source": "/(.*)",
      "headers": [
        { "key": "X-Content-Type-Options", "value": "nosniff" },
        { "key": "X-Frame-Options", "value": "DENY" },
        { "key": "X-XSS-Protection", "value": "1; mode=block" },
        { "key": "Referrer-Policy", "value": "strict-origin-when-cross-origin" },
        { "key": "Permissions-Policy", "value": "camera=(), microphone=(), geolocation=()" },
        {
          "key": "Strict-Transport-Security",
          "value": "max-age=63072000; includeSubDomains; preload"
        },
        {
          "key": "Content-Security-Policy",
          "value": "default-src 'self'; script-src 'self' 'unsafe-inline' https://vercel.live; style-src 'self' 'unsafe-inline'; img-src 'self' data: https:; font-src 'self' https://fonts.gstatic.com; connect-src 'self' https://api.vercel.com"
        }
      ]
    }
  ]
}

Step 3: Security Headers via Edge Middleware

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

export function middleware(request: NextRequest) {
  const response = NextResponse.next();

  // Security headers
  response.headers.set('X-Content-Type-Options', 'nosniff');
  response.headers.set('X-Frame-Options', 'DENY');
  response.headers.set('Referrer-Policy', 'strict-origin-when-cross-origin');
  response.headers.set(
    'Strict-Transport-Security',
    'max-age=63072000; includeSubDomains; preload'
  );

  // Remove server version headers
  response.headers.delete('X-Powered-By');

  return response;
}

Step 4: Deployment Protection

// vercel.json
{
  "deploymentProtection": {
    "preview": "vercel-authentication",
    "optedOutFrom": []
  }
}

Protection options:

• vercel-authentication — requires Vercel team login to view preview deploys
• standard-protection — uses bypass header for automation
• Deployment Protection Bypass — for CI/CD and health checks:

# Generate a bypass secret in Vercel dashboard > Settings > Deployment Protection
# Use in CI with:
curl -H "x-vercel-protection-bypass: your-bypass-secret" \
  https://my-app-preview.vercel.app/api/health

Step 5: Access Token Best Practices

# Create scoped tokens — restrict to one team and project
# Settings > Tokens > Create Token:
# - Scope: Team → your-team
# - Expiration: 90 days (for CI)
# - Permissions: Deployment-only (no team admin)

# Rotate tokens on a schedule
# In CI (GitHub Actions):
# Store as GitHub Secret: VERCEL_TOKEN
# Set expiry alerts in your calendar

Token security rules:

1. Never commit tokens to git — use .env.local or CI secrets
2. Scope tokens to the minimum required permissions
3. Set expiration dates (90 days for CI, 30 days for dev)
4. Rotate immediately if exposed
5. Use separate tokens per environment/pipeline

Step 6: API Route Authentication

// api/protected.ts
import type { VercelRequest, VercelResponse } from '@vercel/node';

export default function handler(req: VercelRequest, res: VercelResponse) {
  // Verify API key from header
  const apiKey = req.headers['x-api-key'];
  if (!apiKey || apiKey !== process.env.INTERNAL_API_KEY) {
    return res.status(401).json({ error: 'Unauthorized' });
  }

  // Verify origin for CORS
  const origin = req.headers.origin;
  const allowedOrigins = (process.env.ALLOWED_ORIGINS ?? '').split(',');
  if (origin && !allowedOrigins.includes(origin)) {
    return res.status(403).json({ error: 'Forbidden origin' });
  }

  res.json({ data: 'protected content' });
}

Security Checklist

Check	Status
No secrets in NEXT_PUBLIC_* variables	Required
Sensitive env vars use type: sensitive	Required
Security headers configured	Required
HSTS enabled with preload	Recommended
Preview deployments protected	Recommended
Access tokens scoped and rotated	Required
CSP configured for your domains	Recommended
.env.local in .gitignore	Required

Output

• Environment variables properly scoped and typed as sensitive
• Security headers applied to all responses
• Deployment protection enabled for preview URLs
• Access tokens scoped with expiration dates

Error Handling

Error	Cause	Solution
Secret visible in client bundle	Prefixed with NEXT_PUBLIC_	Remove prefix, redeploy, rotate the secret
CSP blocking resources	Policy too restrictive	Add the blocked domain to the relevant directive
Preview accessible without auth	Deployment protection disabled	Enable in vercel.json or dashboard
Token expired	Past expiration date	Generate new token, update CI secrets

Resources

• Vercel Security
• Deployment Protection
• Environment Variables
• Security Headers
• Access Tokens

Next Steps

For production deployment checklist, see vercel-prod-checklist.