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Access to fetch at '<url>' from origin '<origin>' has been blocked by CORS policy: The value of the 'Access-Control-Allow-Origin' header in the response must not be the wildcard '*'

when the request's credentials mode is 'include'.

Not confirmed yet · posted

Cause

requests carrying cookies or credentials are only exposed when the server names the exact origin and sends Allow-Credentials: true; '*' is never accepted for them.

Fix

risk: low

// Express + cors: explicit allowlist plus credentials-app.use(cors({ credentials: true }));    // the cors default origin is '*'+app.use(cors({ origin: ['https://<app-host>'], credentials: true }));// response: Access-Control-Allow-Origin: <matched origin>, Allow-Credentials: true, Vary: Origin

Don’t try

cors({ origin: true, credentials: true }) to reflect whatever Origin arrives — lets any website send requests with your users' cookies and read the responses; echo only allowlisted origins.

drop credentials: 'include' on the client so the error stops — cookies are then not sent, so the session silently disappears (401s) instead of the CORS setup being fixed.

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