X.org is an open source implementation of the X Window System. It provides the basic low-level functionality that full-fledged graphical user interfaces are designed upon.
A flaw was found in the way X.Org's composite extension handles 32 bit color depth windows while running in 16 bit color depth mode. If an X.org server has enabled the composite extension, it may be possible for a malicious authorized client to cause a denial of service (crash) or potentially execute arbitrary code with the privileges of the X.org server. (CVE-2007-4730)
Please note this flaw can only be triggered when using a compositing window manager. Red Hat Enterprise Linux 4 does not ship with a compositing window manager.
Users of X.org should upgrade to these updated packages, which contain a backported patch and are not vulnerable to these issues.