This afternoon, Apple released security update 2013-003 for OS X 10.7 Lion and OS X 10.8 Mountain Lion. The Mountain Lion patch is a 20.4MB download, with the Lion version coming in at 61MB. The fixes in the update relate primarily to flaws in QuickTime.
The fixes publicized by Apple involve the QuickTime application and video playback codec. As described by Apple, unpatched, QuickTime can lead to an unexpected application termination or arbitrary code execution in the handling of Sorenson, H.264 videos or ‘mvhd’ atoms.