Apple has released a behemoth of a patch series, this particular one being the seventh conglomerate patching they have done in just the past three months. This series of patches totals 45 separate fixes, both in Apple software and third-party components. Some of the fixes are critical, while others are merely incidental and would require access to the machine already. Eight of the flaws dealt with disk image handling alone:

One focus of the patch is to fix eight vulnerabilities in the way Mac OS X handles disk images, files that when opened appear as a drive within the Macintosh Finder. Mounting a malicious image may lead to an error and could provide a means for an attacker to breach a Mac, Apple said.
Even though many of the flaws were made public some time ago, there hasn't been news of them being exploited, or at least not to the point where Apple would report it. As usual, your Mac will allow you to automatically install these patches or you can download them yourself from their site.