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How to add Cross-Origin-Embedder-Policy on WordPress

Last updated · Reviewed by a CISSP-certified security practitioner

To add Cross-Origin-Embedder-Policy on WordPress, set the header in functions.php (child theme) or a headers plugin with the value require-corp. Requires embedded resources to opt in (enables cross-origin isolation). Clear page caches (plugin + CDN) and curl -I your homepage. Then confirm it with curl -I or a free FixSecurityHeaders scan.

What does Cross-Origin-Embedder-Policy do?

COEP makes the page refuse cross-origin resources that haven't opted in via CORP or CORS. Combined with COOP it enables cross-origin isolation.

Risk if missing: Informational: mainly needed for SharedArrayBuffer and high-precision timers.

What is the WordPress configuration?

Add this to functions.php (child theme) or a headers plugin:

functions.php (child theme) or a headers plugin
<?php
// Child theme functions.php (or a small mu-plugin)
add_action('send_headers', function () {
    header('Cross-Origin-Embedder-Policy: require-corp');
});

How do I add it step by step?

  1. Open functions.php (child theme) or a headers plugin.
  2. Paste the Cross-Origin-Embedder-Policy configuration shown below.
  3. Clear page caches (plugin + CDN) and curl -I your homepage.
  4. Run curl -I https://yourdomain.com and look for the cross-origin-embedder-policy line.
  5. 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-embedder-policy"
# expected:
# cross-origin-embedder-policy: require-corp

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What are the common mistakes?

  • Easily breaks third‑party images, fonts and embeds. Consider credentialless, and only deploy if you need isolation.
  • Prefer setting headers at the web server (nginx/Apache) — PHP headers don't apply to static files.
  • Page-cache plugins may serve cached responses without your headers until purged.

Quick reference

HeaderCross-Origin-Embedder-Policy
Recommended valuerequire-corp
StackWordPress
Wherefunctions.php (child theme) or a headers plugin
ComplianceOWASP ASVS V14.4

FAQ

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

A safe default is require-corp. Easily breaks third‑party images, fonts and embeds. Consider credentialless, and only deploy if you need isolation.

Why isn't Cross-Origin-Embedder-Policy showing up on WordPress?

Prefer setting headers at the web server (nginx/Apache) — PHP headers don't apply to static files. Also clear any CDN or page cache, and check you edited the config that actually serves your domain.

Does Cross-Origin-Embedder-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-Embedder-Policy?

OWASP ASVS V14.4.

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