There is a vulnerability in SUN’s JRE.
From Sun:
A buffer overflow vulnerability in processing GIF images in the Java Runtime Environment may allow an untrusted applet to elevate its privileges. For example, an applet may grant itself permissions to read and write local files or execute local applications with the privileges of the user running the untrusted applet.
There are no reliable symptoms that would indicate the described issue has been exploited.
[tags]Sun, JRE. Java Security, JRE Vulnerability[/tags]