COOP
COOP (Cross-Origin Opener Policy) isolates a top-level window from cross-origin popups, preventing cross-origin window interoperation.
Purpose
To prevent Spectre side channels and cross-origin information leaks caused by cross-origin popups interoperating with the opener.
Mechanism
COOP: same-origin makes cross-origin popups opened via window.open isolated from the opener (opener is null), so cross-origin documents cannot interoperate. same-origin-allow-popups lets same-origin popups keep the opener.
Use cases
- Cross-origin window isolation
- Spectre defense
- Popup security
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