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Fixed invalid CORS wildcard example #28138

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elithrar merged 1 commit into from
Feb 9, 2026
Merged

Fixed invalid CORS wildcard example #28138

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16 changes: 10 additions & 6 deletions src/content/partials/workers/custom_headers.mdx
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Original file line number Diff line number Diff line change
Expand Up @@ -102,16 +102,20 @@ To enable other domains to fetch every static asset from your {props.product ===
Access-Control-Allow-Origin: *
```

This applies the `Access-Control-Allow-Origin` header to any incoming URL. To be more restrictive, you can define a URL pattern that applies to a <code>{props.product === 'workers' ? '\*.\*.workers.dev' : '\*.pages.dev'}</code> subdomain, which then only allows access from its {props.product === 'workers' ? <a href="/workers/configuration/previews/">preview URLs</a> : <><code>staging</code> branch's subdomain</>}:
{props.product === "workers" ? (
<>
This applies the `Access-Control-Allow-Origin` header to any incoming URL. Note that the CORS specification only allows `*`, `null`, or an exact origin as valid `Access-Control-Allow-Origin` values — wildcard patterns within origins are not supported. To allow CORS from specific <a href="/workers/configuration/previews/">preview URLs</a>, you will need to handle this dynamically in your Worker code rather than through the `_headers` file.
</>
) : (
<>
This applies the `Access-Control-Allow-Origin` header to any incoming URL. To be more restrictive, you can define a URL pattern that applies to a <code>{'\*.pages.dev'}</code> subdomain, which then only allows access from its <code>staging</code> branch's subdomain:

<Code
lang="txt"
code={
props.product === "workers"
? `https://:worker.:subdomain.workers.dev/*\n\tAccess-Control-Allow-Origin: https://*-:worker.:subdomain.workers.dev/`
: `https://:project.pages.dev/*\n\tAccess-Control-Allow-Origin: https://staging.:project.pages.dev/`
}
code={`https://:project.pages.dev/*\n\tAccess-Control-Allow-Origin: https://staging.:project.pages.dev/`}
/>
</>
)}

##### Prevent your workers.dev URLs showing in search results

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