> 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/web/dom/xss-dom-via-web-messages.md). # XSS DOM via Web Messages XSS DOM via Web Messages notes for PortSwigger Web Security Academy labs, including exploitation workflow, payload testing, Burp Suite validation, and remediation context. ### DOM XSS Using Web Messages Exploit an XSS-based DOM vulnerability based on web messages (`postMessage`) to cause the `print()` function to be called on the target page by sending a load via the operating server. #### Observed Behaviour (source Code) The page listens to posted messages and directly injects received content into `#ads` element without disinfection:

<script>
   window.addEventListener('message', function(e) {
   document.getElementById('ads').innerHTML = e.data;
   })
</script>

This means that any `e.data` received will be rendered as HTML in `#ads`, opening the door to an XSS DOM if an attacker can post a controlled message.

#### Tests Interactifs (console) Examples of messages sent from the parent's console / d * message texte simple ```javascript window.parent.postMessage('This is a test'); ```

* injection HTML ```javascript window.parent.postMessage('

hello

'); ```

* alert test (XSS) ```jsx window.parent.postMessage("

"); ```

* cause `print()` ( lab lens) ```javascript window.parent.postMessage("

"); ```

#### Iframe Exploit on the Exploit Server Example of the HTML hosted on your server that loads the target page into an iframe and then posts the payload to the load of the iframe: ```mathml ```

To trigger `print()` on the target page, send the payload containing `img` element with `onerror=print()`: ```html ```

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