It was discovered that IcedTea-Web browser plugin incorrectly used the same class loader for applets with the same codebase paths. The default and commonly used codebase value is ".". A malicious applet could use this flaw to gain information about or possibly manipulate other applets currently running in the browser. This could possibly lead to malicious applet's code being executed as part of the other applet.
This issue was discovered by Jiri Vanek of the Red Hat OpenJDK Team.
Fixed now in upstream IcedTea-Web versions 1.2.3 and 1.3.2:
This issue has been addressed in following products:
Red Hat Enterprise Linux 6
Via RHSA-2013:0753 https://rhn.redhat.com/errata/RHSA-2013-0753.html