My old patch of Immunity Debugger's shellcodediff.py script that added support for external binary shellcode files.

shellcodediff2.py

#!/usr/bin/env python

"""
(c) Immunity, Inc. 2004-2008


U{Immunity Inc.<http://www.immunityinc.com>}

Shellcode diff
- Corrected by <MGeeky> to support BINARY 
  external shellcode files

"""

DESC="""Check for badchars"""

from immlib import *
from os.path import dirname
import sys

NAME = "shellcodediff"
USAGE = "address [-b] [shellcode]   // -b stands for binary mode"

def main(args):
    imm = Debugger()
    
    if len(args) < 1:
        imm.log("Usage: !" + NAME + " " + USAGE)
	return "See log window for usage info"

    address  = 0
    length   = 0
    bad_byte_offset = 0
    mangled  = False
    
    address = int(args[0],16)

    shellcode = "shellcode.txt"
    bin = 0
    if len(args) > 1:
        if len(args) == 2:
            if args[1] != '-b':
                shellcode = args[1]
            else:
                bin = 1
        elif len(args) == 3:
            if args[1] == '-b':
                shellcode = args[2]
                bin = 1
            elif args[2] == '-b':
                shellcode = args[1]
                bin = 1
            else:
                return "See log window for usage info"
        else:   return "See log window for usage info"

    m = "TEXT"
    if bin == 1: m = "BIN"

    curdir = dirname(imm.getModule(imm.getDebuggedName()).getPath())
    try:
        fd = open(shellcode,"r"+'b'*bin)
    except:
        fd = open(curdir+'\\'+shellcode, "r"+'b'*bin)
        shellcode = curdir+'\\'+shellcode

    imm.log("[+] Reading '%s' in %s mode shellcode." % (shellcode,m))

    if not fd:
        imm.log("[!] INVALID SHELLCODE file path!")
        return "ERROR"
    
    canvas_shellcode = ""
    # Just pretty this up
    if bin == 0:
        canvas_byte_list = fd.readlines()
        for i in canvas_byte_list:
            canvas_shellcode += i.rstrip("\x0a")
    else:
        data = fd.read()
        for a in data:
            canvas_shellcode += "%02x" % ord(a)

    fd.close()

    length = len(canvas_shellcode) / 2

    id_shellcode = imm.readMemory( address, length )
    id_shellcode = id_shellcode.encode("HEX")
    imm.log("Address: 0x%08x" % address)
    imm.log("SC Len : %d" % length)

    imm.log("CANVAS Shellcode: %s..." % canvas_shellcode[:128])
    imm.log("ID Shellcode:     %s..." % id_shellcode[:128])

    count = 0
    
    # We use the CANVAS shellcode length here again cause
    # presumably its not mangled
    while count < (length*2):

        if id_shellcode[count] != canvas_shellcode[count]:

            imm.log("Missed at byte: %d" % (count/2))
            bad_byte_offset = count
            mangled = True            
            break

        count += 1

    if mangled:
        imm.log(" ")
        imm.log("Bad byte is centered in output with three leading and three trailing bytes.")
        imm.log(" ")
        imm.log("Bad byte at offset: %d" % (bad_byte_offset/2))
        imm.log("Bad byte at address:%08X" % (address + bad_byte_offset/2))
        imm.log("Bad byte value from attacker: %s" % canvas_shellcode[bad_byte_offset:bad_byte_offset+2])
        imm.log("====================")

        imm.log("CANVAS: %s %s %s" % (canvas_shellcode[bad_byte_offset-6:bad_byte_offset],canvas_shellcode[bad_byte_offset:bad_byte_offset+2],canvas_shellcode[bad_byte_offset+2:bad_byte_offset+6]))
        imm.log("ID    : %s %s %s" % (id_shellcode[bad_byte_offset-6:bad_byte_offset], id_shellcode[bad_byte_offset:bad_byte_offset+2],id_shellcode[bad_byte_offset+2:bad_byte_offset+6]))
        
        imm.log("====================")

    else:
        imm.log("Both shellcodes seems to be same.")
        return "SAME"
        

    return "Shellcode diff output to log window."