How to add Cross-Origin-Opener-Policy on Next.js

Last updated November 11, 2026 · Reviewed by a CISSP-certified security practitioner

To add Cross-Origin-Opener-Policy on Next.js, set the header in next.config.js with the value same-origin. Isolates your window from pop-ups and openers on other sites. Restart dev server or redeploy. Then confirm it with curl -I or a free FixSecurityHeaders scan.

What does Cross-Origin-Opener-Policy do?

COOP puts your page in its own browsing context group so cross-origin windows can't get a handle to it.

Risk if missing: Cross-window attacks (XS-Leaks, tabnabbing) and Spectre-style side channels.

What is the Next.js configuration?

Add this to next.config.js:

next.config.js

// next.config.js
module.exports = {
  poweredByHeader: false,
  async headers() {
    return [
      {
        source: "/(.*)",
        headers: [
          { key: "Cross-Origin-Opener-Policy", value: "same-origin" },
        ],
      },
    ];
  },
};

How do I add it step by step?

Open next.config.js.
Paste the Cross-Origin-Opener-Policy configuration shown below.
Restart dev server or redeploy.
Run curl -I https://yourdomain.com and look for the cross-origin-opener-policy line.
Scan your site on FixSecurityHeaders to confirm the grade improved.

How do I verify it worked?

terminal

curl -sI https://yourdomain.com | grep -i "cross-origin-opener-policy"
# expected:
# cross-origin-opener-policy: same-origin

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What are the common mistakes?

OAuth or payment pop-ups that talk back via window.opener may need same-origin-allow-popups.
For nonce-based CSP use middleware.ts instead of static headers.
poweredByHeader: false removes X-Powered-By.

Quick reference

Header	`Cross-Origin-Opener-Policy`
Recommended value	`same-origin`
Stack	Next.js
Where	next.config.js
Compliance	OWASP ASVS V14.4

FAQ

What value should I use for Cross-Origin-Opener-Policy?

A safe default is same-origin. OAuth or payment pop-ups that talk back via window.opener may need same-origin-allow-popups.

Why isn't Cross-Origin-Opener-Policy showing up on Next.js?

For nonce-based CSP use middleware.ts instead of static headers. Also clear any CDN or page cache, and check you edited the config that actually serves your domain.

Does Cross-Origin-Opener-Policy affect SEO or performance?

No measurable performance cost — it's a few bytes per response. It doesn't affect rankings directly, but a misconfigured policy can break page resources, so test before enforcing.

Which compliance frameworks reference Cross-Origin-Opener-Policy?

OWASP ASVS V14.4.