> For the complete documentation index, see [llms.txt](https://hacking-notes.jord4n.pro/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://hacking-notes.jord4n.pro/web/cors/cors-null-origin-trusted.md).
# CORS Null Origin Trusted
CORS Null Origin Trusted notes for PortSwigger Web Security Academy labs, including exploitation workflow, payload testing, Burp Suite validation, and remediation context.
### CORS Vulnerability with Trusted Null Origin
Exploit a vulnerable CORS configuration that trusts the original `"null"`. The objective of the lab is to retrieve the API key from the administrator via a CORS query (with `credentials`) and upload the code to the exploit server. The lab is resolved when the administrator's API key is successfully submitted.
* The server returns `Access-Control-Allow-Credentials: true`.
When the `Origin: jord4n.pro` header is sent, the domain is not reflected.
However, when sending `Origin: null`, the response accepts and reflects this value.
Force a request from a page of `null` origin (e.g. via `iframe` using `srcdoc`) so that the CORS response considers the origin to be trustworthy and returns the data (with cookies using `withCredentials`).
```javascript
```
> Note: the principle is to execute this code from `null` origin (iframe `srcdoc`) so that the CORS response, which accepts `null`, returns sensitive data including cookies.
The recovered key, decoded from Base64:
```bash
echo "NkhBVGdaVWdUb0t2QU5PbXNzanRyY1pDRlpUQUVFYjk=" | base64 -d; echo
6HATgZUgToKvANOmssjtrcZCFZTAEEb9
```
---
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