# SharedArrayBuffer usage is restricted to cross-origin isolated sites

SharedArrayBuffers (SABs) can be used to construct high-resolution timers. High-resolution timers simplify Spectre attacks on cross-origin resources.

To mitigate security risks across browsers, SharedArrayBuffers are gated behind cross-origin isolated contexts starting with Chrome 91 (May 2021). To continue using SharedArrayBuffers, please ensure that this page opts-into cross-origin isolation by setting Cross-Origin-Opener-Policy and Cross-Origin-Embedder-Policy appropriately.

Note that for each iframe, only the first issue is reported for performance reasons.
