Arnaud lightdiscord

writeup-tsg-2021

The challenge is a crackme, it asks for an argument of 32 chars and gives it to a check function.

This check function fork the program multiple times and redirect the stdout of the child to /dev/null.

Every command is done under a nix-shell opened with the following command.

$ nix-shell -p gcc SDL2 steam-run

First thing compile the executable to debug controller hot plugging.

$ gcc ./main.c -o ./main -lSDL2

$ gcc -o a.out *.c && ./a.out
one: 4
two: 4
one: 42
two: 4

The method is the same for both challenges.

When we access the challenge we get two cookies key and password.

	#include <iostream>
	#include <stdexcept>
	#include <vector>
	#include <string>

	template <class T> struct size_of {
	static const int size = sizeof(T);
	};

	template <> struct size_of<void> {

	#include <unistd.h>
	#include <signal.h>
	#include <assert.h>
	#include <stdio.h>
	#include <sys/wait.h>

	void handle_sender(pid_t receiver) {
	for (int i = 0; i < 10; i++) {
	usleep(100);
	puts("Signal sent");

	#include <iostream>
	#include <vector>

	class Item {
	private:
	char identifier;

	public:
	Item(char identifier) : identifier(identifier) {
	std::cout << "Item's " << identifier << " constructor called" << std::endl;

	// Decode the response from the server
	function decode(plain) {
	return String.fromCharCode(...[...plain].map((c) => (c.charCodeAt(0) + 113) % 126))
	}

	$ clang -Wall -Wextra -g3 ./main.c -o main && ./main
	deadbeef