A zero-day vulnerability in Apple s Safari browser could expose millions of Windows users to drive-by download malware attacks. The flaw is currently unpatched. The issue is rated highly critical because of the risk of remote code execution attacks that can lead to complete system takeover. The vulnerability is caused due to an error in the handling of parent windows and can result in a function call using an invalid pointer. This can be exploited to execute arbitrary code when a user e.g. visits a specially crafted web page and closes opened pop-up windows.
Source: https://threatpost.com/secunia-flags-highly-critical-safari-zero-day-flaw-051010/73941/