iDefense Security Advisory 03.30.10 - Remote exploitation of a use after free vulnerability in Microsoft Corp.'s Internet Explorer could allow an attacker to execute arbitrary code with the privileges of the current user. The vulnerability occurs when an HTML object with an 'onreadystatechange' event handler is not properly freed. This event is used to perform actions when the state of some HTML object changes; for example, when a form has data input. Specifically, when certain properties of the object are changed, the event handler function object is freed, but a reference to it remains. When the object is later accessed, this invalid memory is treated as an object pointer, and one of its members is used to make an indirect function call. This results in the execution of arbitrary code.
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