<- HACKTHEBOO CTF

Cult Meeting

2 minutos de lectura

Se nos proporciona un archivo binario llamado meeting:

$ file meeting
meeting: ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=72d8b06e4ca750d5c24395d3349c3121b9b95283, for GNU/Linux 3.2.0, not stripped

Ingeniería inversa

Usando Ghidra, podemos leer el código descompilado en C. Esta es la función main:

int main() {
  int ret;
  char *pointer;
  char input_data[64];
  
  setvbuf(stdout, NULL, 2, 0);
  puts("\x1b[3mYou knock on the door and a panel slides back\x1b[0m");
  puts(&DAT_00102040);
  fwrite("\"What is the password for this week\'s meeting?\" ", 1, 0x30, stdout);  
  fgets(input_data, 0x40, stdin);
  pointer = strchr(input_data, 0xa);
  *pointer = '\0';
  ret = strcmp(input_data, "sup3r_s3cr3t_p455w0rd_f0r_u!");

  if (ret == 0) {
    puts("\x1b[3mThe panel slides closed and the lock clicks\x1b[0m");
    puts("|      | \"Welcome inside...\" ");
    system("/bin/sh");
  } else {
    puts("   \\/");
    puts(&DAT_00102130);
  }

  return 0;
}

Básicamente, el programa solicita una contraseña, y la contraseña esperada está hard-coded: sup3r_s3cr3t_p455w0rd_f0r_u!.

Una vez que introducimos la contraseña correcta, se ejecuta system("/bin/sh").

Flag

Vamos a conectarnos al servidor y a leer la flag:

$ nc 161.35.172.25 31802
You knock on the door and a panel slides back
|/👁️ 👁️ \| A hooded figure looks out at you
"What is the password for this week's meeting?" sup3r_s3cr3t_p455w0rd_f0r_u!  
sup3r_s3cr3t_p455w0rd_f0r_u!
The panel slides closed and the lock clicks
|      | "Welcome inside..."
/bin/sh: 0: can't access tty; job control turned off
$ ls
ls
flag.txt  meeting
$ cat flag.txt
cat flag.txt
HTB{1nf1ltr4t1ng_4_cul7_0f_str1ng5}