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Application & OT Security · Advanced

Cross-Origin Opener Policy (COOP)

An HTTP response header that isolates a page's browsing context group from cross-origin windows that open it or that it opens.

Definition

With Cross-Origin-Opener-Policy: same-origin, a cross-origin page that opened the document loses its window reference, mitigating cross-window attacks such as XS-Leaks and tabnabbing. Combined with Cross-Origin-Embedder-Policy (COEP), it enables cross-origin isolation required for features like SharedArrayBuffer.

Example

Cross-Origin-Opener-Policy: same-origin

Exam tip

COOP plus COEP enables cross-origin isolation.

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