Content Security Policy header present and allows essential resources

A missing Content Security Policy header leaves the application exposed to cross-site scripting via CWE-693 (Protection Mechanism Failure) and is a finding under OWASP A05 (Security Misconfiguration). CSP restricts which scripts, styles, and resources the browser will execute — without it, any XSS vector can load arbitrary scripts from external origins. For SEO, a compromised site that injects spam links or redirects risks Google Safe Browsing flagging, which removes the site from SERPs entirely until manual review clears it. A CSP that blocks analytics scripts is also a failure mode — it silently stops tracking data without an error.

Add CSP headers in next.config.js using the headers() async function. Start with a report-only policy to detect violations before enforcing:

// next.config.js
async headers() {
  return [{
    source: '/(.*)',
    headers: [{
      key: 'Content-Security-Policy',
      value: [
        "default-src 'self'",
        "script-src 'self' 'unsafe-inline' *.google-analytics.com *.vercel-insights.com",
        "style-src 'self' 'unsafe-inline'",
        "img-src 'self' data: https:",
        "font-src 'self' fonts.gstatic.com",
        "connect-src 'self' *.supabase.co *.google-analytics.com",
      ].join('; ')
    }]
  }]
}

Verify with curl -I https://yoursite.com | grep -i content-security-policy. Add report-uri to a CSP reporting endpoint (e.g., Report URI) to catch violations from real users before tightening the policy.

• ID: seo-advanced.technical-seo.content-security-policy

• Severity: low

• What to look for: Count all locations where Content-Security-Policy could be configured: next.config.js headers, middleware, <meta http-equiv="Content-Security-Policy"> tags, and deployment config (vercel.json, netlify.toml). Enumerate the CSP directives found (e.g., default-src, script-src, style-src). Verify the policy does not block analytics scripts, monitoring tools, or other essential resources.

• Pass criteria: CSP header is present in at least 1 configuration location with at least 3 directives defined, and the policy does not block essential external resources (analytics, CDN assets, font providers). Report: "CSP configured with X directives; 0 essential resources blocked."

• Fail criteria: No CSP header found in any configuration, or CSP blocks at least 1 essential resource (analytics, CDN, fonts).

• Skip (N/A) when: No external resources are loaded by the application (no analytics, no external scripts, no CDN assets).

• Detail on fail: "No Content-Security-Policy header found in next.config.js, middleware, or deployment config" or "CSP script-src blocks Google Analytics (*.google-analytics.com not in allowlist)".

• Remediation: Add CSP header in next.config.js headers configuration:

  // next.config.js
  async headers() {
    return [{
      source: '/(.*)',
      headers: [{
        key: 'Content-Security-Policy',
        value: "default-src 'self'; script-src 'self' *.google-analytics.com; style-src 'self' 'unsafe-inline'"
      }]
    }]
  }