Software Engineering Institute

Apple QuickTime is a media player that includes a browser plugin. QuickTime for Java provides APIs which allow Java developers to include multimedia in Java applets.

From Apple Article ID: 306896 "About the security content of QuickTime 7.3":
Multiple vulnerabilities exist in QuickTime for Java, which may allow untrusted Java applets to obtain elevated privileges. By enticing a user to visit a web page containing a maliciously crafted Java applet, an attacker may cause the disclosure of sensitive information and arbitrary code execution with elevated privileges. This update addresses the issues by making QuickTime for Java no longer accessible to untrusted Java applets. Credit to Adam Gowdiak for reporting this issue.

To exploit this vulnerability, an attacker would have to convince a user to open a specially crafted Java applet which could be hosted on a webpage.

A remote, unauthenticated attacker may be able to take any action that the user running QuickTime can.

Upgrade
Apple has addressed this issue in QuickTime 7.3.

Disable Java
Until updates can be applied, disabling the Java plugin may mitigate this vulnerability. For instructions on how to disable Java in your browser, see Securing Your Web Browser.