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index.md
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---
title: "Reason: CORS header 'Origin' cannot be added"
slug: Web/HTTP/CORS/Errors/CORSOriginHeaderNotAdded
page-type: http-cors-error
---
{{HTTPSidebar}}
## Reason
```plain
Reason: CORS header 'Origin' cannot be added
```
## What went wrong?
The {{Glossary("user agent")}} was unable to add the required {{HTTPHeader("Origin")}}
header to the {{Glossary("HTTP")}} request. All CORS requests must have an
`Origin` header.
This can happen if the JavaScript code is running with enhanced privileges allowing it
access to multiple domains' content, for example.
## See also
- [CORS errors](/en-US/docs/Web/HTTP/CORS/Errors)
- Glossary: {{Glossary("CORS")}}
- [CORS introduction](/en-US/docs/Web/HTTP/CORS)