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#!/usr/bin/env ruby
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##
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# This module requires Metasploit: https://metasploit.com/download
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# Current source: https://github.com/rapid7/metasploit-framework
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##
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#
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# This script is intended to assist an exploit developer in deducing what
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# "bad characters" exist for a given input path to a program.
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#
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begin
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msfbase = __FILE__
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while File.symlink?(msfbase)
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  msfbase = File.expand_path(File.readlink(msfbase), File.dirname(msfbase))
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end
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gem 'rex-text'
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$:.unshift(File.expand_path(File.join(File.dirname(msfbase), '..', '..', 'lib')))
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require 'msfenv'
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$:.unshift(ENV['MSF_LOCAL_LIB']) if ENV['MSF_LOCAL_LIB']
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require 'rex'
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OutStatus = "[*] "
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OutError  = "[-] "
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$args = Rex::Parser::Arguments.new(
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  "-b" => [ true, "The list of characters to avoid: '\\x00\\xff'"                      ],
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  "-h" => [ false, "Help banner"                                                       ],
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  "-i" => [ true, "Read memory contents from the supplied file path"                   ],
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  "-t" => [ true, "The format that the memory contents are in (empty to list)"         ])
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def usage
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  $stderr.puts("\n" + "    Usage: #{File.basename($0)} <options>\n" + $args.usage)
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  exit
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end
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def show_format_list
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  $stderr.puts("Supported formats:\n")
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  $stderr.puts("  raw      raw binary data\n")
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  $stderr.puts("  windbg   output from windbg's \"db\" command\n")
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  $stderr.puts("  gdb      output from gdb's \"x/bx\" command\n")
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  $stderr.puts("  hex      hex bytes like \"\\xFF\\x41\" or \"eb fe\"\n")
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end
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def debug_buffer(name, buf)
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  str = "\n#{buf.length} bytes of "
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  str << name
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  str += ":" if buf.length > 0
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  str += "\n\n"
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  $stderr.puts str
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  if buf.length > 0
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    $stderr.puts Rex::Text.to_hex_dump(buf)
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  end
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end
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# Input defaults
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badchars = ''
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fmt      = 'raw'
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input    = $stdin
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# Output
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new_badchars = ''
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# Parse the argument and rock it
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$args.parse(ARGV) { |opt, idx, val|
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  case opt
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    when "-i"
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      begin
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        input = File.new(val)
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      rescue
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        $stderr.puts(OutError + "Failed to open file #{val}: #{$!}")
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        exit
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      end
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    when "-b"
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      badchars = Rex::Text.dehex(val)
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    when "-t"
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      if (val =~ /^(raw|windbg|gdb|hex)$/)
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        fmt = val
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      else
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        if val.nil? or val.length < 1
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          show_format_list
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        else
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          $stderr.puts(OutError + "Invalid format: #{val}")
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        end
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        exit
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      end
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    when "-h"
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      usage
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  end
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}
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if input == $stdin
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  $stderr.puts(OutStatus + "Please paste the memory contents in \"" + fmt + "\" format below (end with EOF):\n")
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end
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# Working data set
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from_msf = Rex::Text.charset_exclude(badchars)
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from_dbg = ''
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# Process the input
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from_dbg = input.read
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case fmt
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  when "raw"
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    # this should already be in the correct format :)
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  when "windbg"
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    translated = ''
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    from_dbg.each_line do |ln|
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      translated << ln.chomp[10,47].gsub!(/(-| )/, '')
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    end
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    from_dbg = Rex::Text.hex_to_raw(translated)
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  when "gdb"
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    translated = ''
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    from_dbg.each_line do |ln|
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      translated << ln.chomp.split(':')[1].gsub!(/0x/, '\x').gsub!(/ /, '')
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    end
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    from_dbg = Rex::Text.hex_to_raw(translated)
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  when "hex"
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    translated = ''
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    from_dbg.each_line do |ln|
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      translated << ln.chomp.gsub!(/ /,'')
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    end
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    from_dbg = Rex::Text.hex_to_raw(translated)
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end
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=begin
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# Uncomment these to debug stuff ..
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debug_buffer("BadChars", badchars)
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debug_buffer("memory contents", from_dbg)
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debug_buffer("Rex::Text.charset_exclude() output", from_msf)
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=end
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# Find differences between the two data sets
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from_msf = from_msf.unpack('C*')
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from_dbg = from_dbg.unpack('C*')
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minlen = from_msf.length
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minlen = from_dbg.length if from_dbg.length < minlen
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(0..(minlen-1)).each do |idx|
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  ch1 = from_msf[idx]
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  ch2 = from_dbg[idx]
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  if ch1 != ch2
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    str = "Byte at index 0x%04x differs (0x%02x became 0x%02x)" % [idx, ch1, ch2]
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    $stderr.puts OutStatus + str
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    new_badchars << ch1
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  end
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end
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# show the results
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if new_badchars.length < 1
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  $stderr.puts(OutStatus + "All characters matched, no new bad characters discovered.")
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else
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  $stderr.puts(OutStatus + "Proposed BadChars: \"" + Rex::Text.to_hex(new_badchars) + "\"")
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end
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rescue SignalException => e
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  puts("Aborted! #{e}")
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end
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