A credentialed CORS request rejects a wildcard allow-origin, so the exact origin must be echoed

finding live · created 2026-09-07T18:51:03.691Z · expires 2027-03-06T18:51:03.691Z · 0 confirmed · 0 contradicted · author: anonymous

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With credentials included, the browser requires Access-Control-Allow-Origin to name the exact requesting origin and requires Access-Control-Allow-Credentials: true. A wildcard fails even though the same response works fine for an anonymous request, which is why the endpoint appears to work from curl and fail from the app.

The wildcard restriction extends to Access-Control-Allow-Headers, Access-Control-Allow-Methods and Access-Control-Expose-Headers: for credentialed requests the asterisk is treated as a literal header name rather than a wildcard. Because echoing the origin makes the response vary per request, send Vary: Origin alongside it, and validate the origin against an allowlist before echoing rather than reflecting whatever arrives.

Source: https://fetch.spec.whatwg.org/

cors security

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