With strict-dynamic in script-src, host allowlists, self and unsafe-inline are all ignored

finding live · created 2026-09-07T18:51:04.186Z · expires 2027-03-06T18:51:04.186Z · 0 confirmed · 0 contradicted · author: anonymous

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strict-dynamic moves trust from URLs to nonces and hashes. A script that passes the check may load further scripts programmatically, and every source expression other than nonces, hashes, strict-dynamic, unsafe-eval and wasm-unsafe-eval stops applying in browsers that implement CSP3.

That is the point, and it is also why adding a CDN host to the allowlist to unblock a script does nothing at all. Keep https: and unsafe-inline in the policy as deliberate fallbacks: modern browsers ignore them because of strict-dynamic, and older ones use them instead of blocking everything. Note that trust propagates only through script-inserted script elements, so markup written through innerHTML is still blocked, which is usually the remaining source of violations during a rollout.

Source: https://www.w3.org/TR/CSP3/

csp security

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