Class: Msf::Encoder::XorAdditiveFeedback

Inherits:
Xor show all
Defined in:
lib/msf/core/encoder/xor_additive_feedback.rb

Overview

This class performs per-block XOR additive feedback encoding.

Constant Summary

Constants inherited from Module

Module::REPLICANT_EXTENSION_DS_KEY

Constants included from Module::ModuleInfo

Module::ModuleInfo::UpdateableOptions

Instance Attribute Summary

Attributes inherited from Msf::Encoder

#available_space

Attributes inherited from Module

#error, #job_id, #license, #platform, #privileged, #references, #user_data

Attributes included from Framework::Offspring

#framework

Attributes included from Module::UUID

#uuid

Attributes included from Rex::Ui::Subscriber::Input

#user_input

Attributes included from Rex::Ui::Subscriber::Output

#user_output

Attributes included from Module::Privileged

#priveli, #privileged

Attributes included from Module::Options

#options

Attributes included from Module::ModuleStore

#module_store

Attributes included from Module::ModuleInfo

#module_info

Attributes included from Module::FullName

#aliased_as

Attributes included from Module::DataStore

#datastore

Attributes included from Module::Author

#author

Attributes included from Module::Arch

#arch

Attributes included from Module::Alert

#alerts, #you_have_been_warned

Instance Method Summary collapse

Methods inherited from Xor

#find_bad_keys

Methods inherited from Msf::Encoder

#can_preserve_registers?, #decoder_block_size, #decoder_hash, #decoder_key_offset, #decoder_key_pack, #decoder_key_size, #decoder_stub, #do_encode, #encode, #encode_begin, #encode_end, #encode_finalize_stub, #encoder_type, #find_bad_keys, #find_context_key, #find_key_verify, #has_badchars?, #init_platform, #init_state, #integer_to_key_bytes, #key_bytes_to_buffer, #key_bytes_to_integer, #modified_registers, #obtain_key, #prepend_buf, #preserves_stack?, #to_native, #type, type

Methods inherited from Module

#adapted_refname, #adapter_refname, #black_listed_auth_filenames, cached?, #debugging?, #default_cred?, #default_options, #fail_with, #file_path, #framework, #has_check?, #orig_cls, #owner, #perform_extensions, #platform?, #platform_to_s, #post_auth?, #register_extensions, #register_parent, #replicant, #required_cred_options, #set_defaults, #stage_refname, #stager_refname, #workspace

Methods included from Module::Reliability

#reliability, #reliability_to_s

Methods included from Module::Stability

#stability, #stability_to_s

Methods included from Module::SideEffects

#side_effects, #side_effects_to_s

Methods included from Module::UUID

#generate_uuid

Methods included from Module::UI

#init_ui

Methods included from Module::UI::Message

#print_error, #print_good, #print_prefix, #print_status, #print_warning

Methods included from Module::UI::Message::Verbose

#vprint_error, #vprint_good, #vprint_status, #vprint_warning

Methods included from Module::UI::Line

#print_line, #print_line_prefix

Methods included from Module::UI::Line::Verbose

#vprint_line

Methods included from Rex::Ui::Subscriber

#copy_ui, #init_ui, #reset_ui

Methods included from Rex::Ui::Subscriber::Input

#gets

Methods included from Rex::Ui::Subscriber::Output

#flush, #print, #print_blank_line, #print_error, #print_good, #print_line, #print_status, #print_warning

Methods included from Module::Type

#auxiliary?, #encoder?, #evasion?, #exploit?, #nop?, #payload?, #post?, #type

Methods included from Module::Ranking

#rank, #rank_to_h, #rank_to_s

Methods included from Module::Privileged

#privileged?

Methods included from Module::Options

#deregister_option_group, #deregister_options, #register_advanced_options, #register_evasion_options, #register_option_group, #register_options, #validate

Methods included from Module::Network

#comm, #support_ipv6?, #target_host, #target_port

Methods included from Module::ModuleStore

#[], #[]=

Methods included from Module::ModuleInfo

#alias, #description, #disclosure_date, #info_fixups, #merge_check_key, #merge_info, #merge_info_advanced_options, #merge_info_alias, #merge_info_description, #merge_info_evasion_options, #merge_info_name, #merge_info_options, #merge_info_string, #merge_info_version, #name, #notes, #update_info

Methods included from Module::FullName

#aliases, #fullname, #promptname, #realname, #refname, #shortname

Methods included from Module::DataStore

#import_defaults, #import_target_defaults, #share_datastore

Methods included from Module::Compatibility

#compat, #compatible?, #init_compat

Methods included from Module::Author

#author_to_s, #each_author

Methods included from Module::Auth

#store_valid_credential

Methods included from Module::Arch

#arch?, #arch_to_s, #each_arch

Methods included from Module::Alert

#add_alert, #add_error, #add_info, #add_warning, #alert_user, #errors, #get_alerts, included, #infos, #is_usable?, #warnings, #without_prompt

Constructor Details

#initialize(info) ⇒ XorAdditiveFeedback

Returns a new instance of XorAdditiveFeedback.



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# File 'lib/msf/core/encoder/xor_additive_feedback.rb', line 10

def initialize(info)
  super(info)
end

Instance Method Details

#encode_block(state, block) ⇒ Object

Encodes a block using the XOR additive feedback algorithm.



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# File 'lib/msf/core/encoder/xor_additive_feedback.rb', line 17

def encode_block(state, block)
  # XOR the key with the current block
  orig       = block.unpack(decoder_key_pack)[0]
  oblock     = orig ^ state.key

  # Add the original block contents to the key
  state.key  = (state.key + orig) % (1 << (decoder_key_size * 8))

  # Return the XOR'd block
  return [ oblock ].pack(decoder_key_pack)
end

#find_key(buf, badchars, state = Msf::EncoderState.new) ⇒ Object

Finds a key that is compatible with the badchars list.



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# File 'lib/msf/core/encoder/xor_additive_feedback.rb', line 32

def find_key(buf, badchars, state = Msf::EncoderState.new)
  key_bytes = integer_to_key_bytes(super(buf, badchars, nil))
  valid = false

  # Save the original key_bytes so we can tell if we loop around
  orig_key_bytes = key_bytes.dup

  # While we haven't found a valid key, keep trying the encode operation
  while (!valid)
    # Initialize the state back to defaults since we're trying to find a
    # key.
    init_state(state)

    begin
      # Reset the encoder state's key to the current set of key bytes
      state.reset(key_bytes_to_integer(key_bytes))

      # If the key itself contains a bad character, throw the bad
      # character exception with the index of the bad character in the
      # key.  Use a stub_size of zero to bypass the check to in the
      # rescue block.
      if ((idx = has_badchars?([state.key.to_i].pack(decoder_key_pack), badchars)) != nil)
        raise Msf::BadcharError.new(nil, idx, 0, nil)
      end

      # Perform the encode operation...if it encounters a bad character
      # an exception will be thrown
      valid = do_encode(state)
    rescue Msf::BadcharError => info
      # If the decoder stub contains a bad character, then there's not
      # much we can do about it
      if (info.index < info.stub_size)
        raise info, "The #{self.name} decoder stub contains a bad character.", caller
      end

      # Determine the actual index to the bad character inside the
      # encoded payload by removing the decoder stub from the index and
      # modulus off the decoder's key size
      idx = (info.index - info.stub_size) % (decoder_key_size)

      # Increment the key byte at the index that the bad character was
      # detected
      key_bytes[idx] = ((key_bytes[idx] + 1) % 255)

      # If we looped around, then give up.
      if (key_bytes[idx] == orig_key_bytes[idx])
        raise info, "The #{self.name} encoder failed to encode without bad characters.",
            caller
      end
    end
  end

  # Return the original key
  return state.orig_key
end