That's another way of saying should an attacker exploit these flaws, they can run whatever attack tools and exploit code they wish on your system.
Such flaws can be exploited through attackers establishing maliciously crafted web sites, for example.
The Safari 5.0.3 update can be accessed here for Mac OS X Snow Leopard, Leopard, Windows 7, Windows Vista, and Windows XP. It's the third Safari update since Safari 5 was released this Spring.
And it's an update you'll want to apply immediately.
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