Use COOP, COEP, and CORP for cross-origin isolation when needed

Cross-origin isolation reduces opener-based attacks and XS-Leak risk, and it is required for powerful browser features such as SharedArrayBuffer in modern browsers. It also breaks integrations if deployed carelessly, so it needs a deliberate rollout rather than a copy-pasted header block.

Quick Reference

• Use Cross-Origin-Opener-Policy and Cross-Origin-Embedder-Policy together when you need cross-origin isolation
• Audit every cross-origin script, iframe, image, worker, and font before enforcing COEP
• Serve embeddable resources with CORS or Cross-Origin-Resource-Policy as appropriate
• Verify self.crossOriginIsolated === true before depending on isolated-only features

Check

Review security headers and embedded resources for cross-origin isolation. Check whether the app needs COOP/COEP, whether resources are compatible with COEP, and whether the runtime actually becomes crossOriginIsolated.

Fix

Add COOP and COEP only after auditing dependencies, ensure subresources use CORP or CORS as required, and verify the final document becomes crossOriginIsolated in the browser.