What is it? @.@

Here is the place where I record some tactics about wargame, systems, and other security issues.


Hack This Site! - Extbasic 14


1337 race condition.

Level 14

Sam was trying to make a program to show how 1337 he is. But the output isn't always correct. Help him fix his program so he can impress his friends.

package org.hackthissite.missions.extbasic;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class ExtBasic14 {

        private final ExecutorService executorService = Executors.newFixedThreadPool(100);
        private static final int MAX = 1337;
        private int timeToGetLeet = 0;

        ExtBasic14() throws InterruptedException {
                for (int i = 0; i < MAX; i++) {
                        executorService.execute(new Runnable() {
                                public void run() {
                while (!executorService.isTerminated()) {

        private void incrementLeetness() {
                int obfusticatedIncremental = timeToGetLeet;
                obfusticatedIncremental = obfusticatedIncremental + 1;
                timeToGetLeet = obfusticatedIncremental;

         * @param args

        public static void main(String[] args) throws InterruptedException {
                new ExtBasic14();



  1. ExecutorService has to use a thread safe queue (Which it does by default). This is all that is needed.
  2. It is necessary to synchronize the ExecutorService object in the incrementLeetness method since the incrementLeetness method can be called from differens threads.
  3. Input "private synchronized void incrementLeetness() {" and check.
  4. It's done.
  5. Congratz! You have completed all the missions in this category