Java 1.4.2 before 1.4.2 Release 2 on Apple Mac OS X does not prevent multiple programs from opening the same port as a Java ServerSocket, which allows local users to operate a Java program that intercepts network data intended for the ServerSocket of a different Java program.
Sun Java 1.3.1, 1.4.1, and 1.4.2 allows local users to cause a denial of service (JVM crash), possibly by calling the ClassDepth function with a null parameter, which causes a crash instead of generating a null pointer exception.