Vulnerability in Java Runtime Environment (JRE) allows remote malicious web sites to hijack or sniff a web client's sessions, when an HTTP proxy is being used, via a Java applet that redirects the session to another server, as seen in (1) Netscape 6.0 through 6.1 and 4.79 and earlier, (2) Microsoft VM build 3802 and earlier as used in Internet Explorer 4.x and 5.x, and possibly other implementations that use vulnerable versions of SDK or JDK.