You might harden policy files for Java process to prevent usage of Runtime. Not sure about any attack vectors, but I can execute linux commands. Also interesting that you allowed threads.

import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; class Solution {

    public static void main(String[] args) throws IOException, InterruptedException {
        final Runtime rt = Runtime.getRuntime();
        final Process pr = rt.exec("uname -a");
        new Thread(new Runnable() {
            public void run() {
                BufferedReader input = new BufferedReader(new InputStreamReader(pr.getInputStream()));
                String line = null;

                try {
                    while ((line = input.readLine()) != null)
                        System.out.println(line);
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }).start();

        pr.waitFor();
    }
	
		
}