metasploit-framework/modules/encoders/x86/nonupper.rb

##
# This module requires Metasploit: https://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##

require 'rex/encoder/nonupper'

class MetasploitModule < Msf::Encoder::NonUpper
  Rank = LowRanking

  def initialize
    super(
      'Name'             => "Non-Upper Encoder",
      'Description'      => %q{
          Encodes payloads as non-alpha based bytes. This allows
        payloads to bypass tolower() calls, but will fail isalpha().
        Table based design from Russel Sanford.
      },
      'Author'           => [ 'pusscat'],
      'Arch'             => ARCH_X86,
      'License'          => BSD_LICENSE,
      'EncoderType'      => Msf::Encoder::Type::NonUpper,
      'Decoder'          =>
        {
          'BlockSize' => 1,
        })
  end

  #
  # Returns the decoder stub that is adjusted for the size of the buffer
  # being encoded.
  #
  def decoder_stub(state)
    state.key                   = ""
    state.decoder_key_size      = 0
    Rex::Encoder::NonUpper::gen_decoder()
  end

  #
  # Encodes a one byte block with the current index of the length of the
  # payload.
  #
  def encode_block(state, block)
    begin
      newchar, state.key, state.decoder_key_size =
        Rex::Encoder::NonUpper::encode_byte(datastore['BadChars'], block.unpack('C')[0], state.key, state.decoder_key_size)
    rescue RuntimeError => e
      # This is a bandaid to deal with the fact that, since it's in
      # the Rex namespace, the encoder itself doesn't have access to the
      # Msf exception classes.  Turn it into an actual EncodingError
      # exception so the encoder doesn't look broken when it just fails
      # to encode.
      raise BadcharError if e.message == "BadChar"
    end
    return newchar
  end

  #
  # Fix stuff, and add the table :)
  #
  def encode_end(state)
    state.encoded.gsub!(/A/, state.decoder_key_size.chr)
    state.encoded.gsub!(/B/, (state.decoder_key_size+5).chr)
    state.encoded[0x24, 0] = state.key
  end
end