Secure Static Versioning in Sun Java JDK and JRE 6 Update 6 and earlier, and 5.0 Update 6 through 15, does not properly prevent execution of applets on older JRE releases, which might allow remote attackers to exploit vulnerabilities in these older releases.

More... (http://nvd.nist.gov/nvd.cfm?cvename=CVE-2008-3115)