Class: Rex::Post::Meterpreter::Packet

Inherits:
GroupTlv show all
Defined in:
lib/rex/post/meterpreter/packet.rb

Overview

The logical meterpreter packet class

Constant Summary collapse

XOR_KEY_SIZE =

The Packet container itself has a custom header that is slightly different than the typical TLV packets. The header contains the following:

XOR KEY - 4 bytes Session GUID - 16 bytes Encrypt flags - 4 bytes Packet length - 4 bytes Packet type - 4 bytes Packet data - X bytes

If the encrypt flags are zero, then the Packet data is just straight TLV values as per the normal TLV packet structure.

If the encrypt flags are non-zer, then the Packet data is encrypted based on the scheme.

Flag == 1 (AES256)

IV             - 16 bytes
Encrypted data - X bytes

The key that is required to decrypt the data is stored alongside the session data, and hence when the packet is initially parsed, only the header is accessed. The packet itself will need to be decrypted on the fly at the point that it is required and at that point the decryption key needs to be provided.

4
ENCRYPTED_FLAGS_SIZE = 
4
PACKET_LENGTH_SIZE = 
4
PACKET_TYPE_SIZE = 
4
PACKET_HEADER_SIZE = 
XOR_KEY_SIZE + GUID_SIZE + ENCRYPTED_FLAGS_SIZE + PACKET_LENGTH_SIZE + PACKET_TYPE_SIZE
AES_IV_SIZE = 
16
ENC_FLAG_NONE = 
0x0
ENC_FLAG_AES256 = 
0x1
ENC_FLAG_AES128 = 
0x2

Constants inherited from Tlv

Tlv::HEADER_SIZE

Instance Attribute Summary collapse

Attributes inherited from GroupTlv

#tlvs

Attributes inherited from Tlv

#compress, #type, #value

Class Method Summary collapse

Instance Method Summary collapse

Methods inherited from GroupTlv

#add_tlv, #add_tlvs, #each, #each_tlv, #each_tlv_with_index, #each_with_index, #get_tlv, #get_tlv_value, #get_tlv_values, #get_tlvs, #has_tlv?, #reset

Methods inherited from Tlv

#htonq, #inspect, #meta_type?, #ntohq, #type?, #value?

Constructor Details

#initialize(type = nil, method = nil) ⇒ Packet

Initializes the packet to the supplied packet type and method, if any. If the packet is a request, a request identifier is created.


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# File 'lib/rex/post/meterpreter/packet.rb', line 1225

def initialize(type = nil, method = nil)
  super(type)

  if method
    self.method = method
  end

  self.created_at = ::Time.now
  self.raw = ''

  # If it's a request, generate a random request identifier
  if ((type == PACKET_TYPE_REQUEST) ||
      (type == PACKET_TYPE_PLAIN_REQUEST))
    rid = ''

    32.times { |val| rid << rand(10).to_s }

    add_tlv(TLV_TYPE_REQUEST_ID, rid)
  end
end

Instance Attribute Details

#created_at ⇒ Object

Returns the value of attribute created_at


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# File 'lib/rex/post/meterpreter/packet.rb', line 1126

def created_at
  @created_at
end

#encrypt_flags ⇒ Object

Returns the value of attribute encrypt_flags


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# File 'lib/rex/post/meterpreter/packet.rb', line 1129

def encrypt_flags
  @encrypt_flags
end

#length ⇒ Object

Returns the value of attribute length


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# File 'lib/rex/post/meterpreter/packet.rb', line 1130

def length
  @length
end

#raw ⇒ Object

Returns the value of attribute raw


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# File 'lib/rex/post/meterpreter/packet.rb', line 1127

def raw
  @raw
end

#session_guid ⇒ Object

Returns the value of attribute session_guid


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# File 'lib/rex/post/meterpreter/packet.rb', line 1128

def session_guid
  @session_guid
end

Class Method Details

.create_request(method = nil) ⇒ Object

Creates a request with the supplied method.


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# File 'lib/rex/post/meterpreter/packet.rb', line 1181

def Packet.create_request(method = nil)
  Packet.new(PACKET_TYPE_REQUEST, method)
end

.create_response(request = nil) ⇒ Object

Creates a response to a request if one is provided.


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# File 'lib/rex/post/meterpreter/packet.rb', line 1188

def Packet.create_response(request = nil)
  response_type = PACKET_TYPE_RESPONSE
  method = nil
  id = nil

  if (request)
    if (request.type?(PACKET_TYPE_PLAIN_REQUEST))
      response_type = PACKET_TYPE_PLAIN_RESPONSE
    end

    method = request.method

    if request.has_tlv?(TLV_TYPE_REQUEST_ID)
      id = request.get_tlv_value(TLV_TYPE_REQUEST_ID)
    end
  end

  packet = Packet.new(response_type, method)

  if id
    packet.add_tlv(TLV_TYPE_REQUEST_ID, id)
  end

  packet
end

Instance Method Details

#add_raw(bytes) ⇒ Object 


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# File 'lib/rex/post/meterpreter/packet.rb', line 1246

def add_raw(bytes)
  self.raw << bytes
end

#aes_decrypt(key, iv, data) ⇒ Object

Raises:


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# File 'lib/rex/post/meterpreter/packet.rb', line 1283

def aes_decrypt(key, iv, data)
  size = key.length * 8
  raise ArgumentError.new('AES key width must be 128 or 256 bits') unless (size == 128 || size == 256)
  # Create the required cipher instance
  aes = OpenSSL::Cipher.new("AES-#{size}-CBC")
  # Generate a truly random IV

  # set up the encryption
  aes.decrypt
  aes.key = key
  aes.iv = iv

  # decrypt!
  aes.update(data) + aes.final
end

#aes_encrypt(key, data) ⇒ Object

Raises:


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# File 'lib/rex/post/meterpreter/packet.rb', line 1266

def aes_encrypt(key, data)
  size = key.length * 8
  raise ArgumentError.new('AES key width must be 128 or 256 bits') unless (size == 128 || size == 256)
  # Create the required cipher instance
  aes = OpenSSL::Cipher.new("AES-#{size}-CBC")
  # Generate a truly random IV
  iv = aes.random_iv

  # set up the encryption
  aes.encrypt
  aes.key = key
  aes.iv = iv

  # encrypt and return the IV along with the result
  return iv, aes.update(data) + aes.final
end

#decrypt_packet(key, encrypt_flags, data) ⇒ Object

Decrypt the packet based on the content of the encryption flags.


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# File 'lib/rex/post/meterpreter/packet.rb', line 1327

def decrypt_packet(key, encrypt_flags, data)
  # TODO: throw an error if the expected encryption isn't the same as the given
  #       as this could be an indication of hijacking or side-channel packet addition
  #       as highlighted by Justin Steven on github.
  if key && key[:key] && key[:type] && encrypt_flags == key[:type] && (encrypt_flags == ENC_FLAG_AES128 || encrypt_flags == ENC_FLAG_AES256)
    iv = data[0, AES_IV_SIZE]
    aes_decrypt(key[:key], iv, data[iv.length..-1])
  else
    data
  end
end

#from_r(key = nil) ⇒ Object

Override the function that reads from a raw byte stream so that the XORing of data is included in the process prior to passing it on to the default functionality that can parse the TLV values.


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# File 'lib/rex/post/meterpreter/packet.rb', line 1351

def from_r(key=nil)
  self.parse_header!
  xor_key = self.raw.unpack('a4')[0]
  data = xor_bytes(xor_key, self.raw[PACKET_HEADER_SIZE..-1])
  raw = decrypt_packet(key, self.encrypt_flags, data)
  super([self.length, self.type, raw].pack('NNA*'))
end

#method ⇒ Object

Returns the value of the packet's method TLV.


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# File 'lib/rex/post/meterpreter/packet.rb', line 1410

def method
  get_tlv_value(TLV_TYPE_COMMAND_ID)
end

#method=(method) ⇒ Object

Sets the packet's method TLV to the method supplied.

Raises:


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# File 'lib/rex/post/meterpreter/packet.rb', line 1402

def method=(method)
  raise ArgumentError.new("Packet.method must be an integer. Current value is #{method}") unless method.is_a?(Integer)
  add_tlv(TLV_TYPE_COMMAND_ID, method, true)
end

#method?(method) ⇒ Boolean

Checks to see if the packet's method is equal to the supplied method.

Returns:

  • (Boolean) 

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# File 'lib/rex/post/meterpreter/packet.rb', line 1395

def method?(method)
  (get_tlv_value(TLV_TYPE_COMMAND_ID) == method)
end

#parse_header! ⇒ Object 


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# File 'lib/rex/post/meterpreter/packet.rb', line 1339

def parse_header!
  xor_key = self.raw.unpack('a4')[0]
  data = xor_bytes(xor_key, self.raw[0..PACKET_HEADER_SIZE])
  _, self.session_guid, self.encrypt_flags, self.length, self.type = data.unpack('a4a16NNN')
end

#raw_bytes_required ⇒ Object 


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# File 'lib/rex/post/meterpreter/packet.rb', line 1250

def raw_bytes_required
  # if we have the xor bytes and length ...
  if self.raw.length >= PACKET_HEADER_SIZE
    # return a value based on the length of the data indicated by
    # the header
    xor_key = self.raw.unpack('a4')[0]
    decoded_bytes = xor_bytes(xor_key, raw[0, PACKET_HEADER_SIZE])
    _, _, _, length, _ = decoded_bytes.unpack('a4a16NNN')
    length + PACKET_HEADER_SIZE - HEADER_SIZE - self.raw.length
  else
    # Otherwise ask for the remaining bytes for the metadata to get the packet length
    # So we can do the rest of the calculation next time
    PACKET_HEADER_SIZE - self.raw.length
  end
end

#response? ⇒ Boolean

Checks to see if the packet is a response.

Returns:

  • (Boolean) 

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# File 'lib/rex/post/meterpreter/packet.rb', line 1382

def response?
  (self.type == PACKET_TYPE_RESPONSE || self.type == PACKET_TYPE_PLAIN_RESPONSE)
end

#result ⇒ Object

Gets the value of the packet's result TLV.


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# File 'lib/rex/post/meterpreter/packet.rb', line 1432

def result
  get_tlv_value(TLV_TYPE_RESULT)
end

#result=(result) ⇒ Object

Sets the packet's result TLV.


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# File 'lib/rex/post/meterpreter/packet.rb', line 1425

def result=(result)
  add_tlv(TLV_TYPE_RESULT, result, true)
end

#result?(result) ⇒ Boolean

Checks to see if the packet's result value is equal to the supplied result.

Returns:

  • (Boolean) 

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# File 'lib/rex/post/meterpreter/packet.rb', line 1418

def result?(result)
  (get_tlv_value(TLV_TYPE_RESULT) == result)
end

#rid ⇒ Object

Gets the value of the packet's request identifier TLV.


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# File 'lib/rex/post/meterpreter/packet.rb', line 1439

def rid
  get_tlv_value(TLV_TYPE_REQUEST_ID)
end

#to_r(session_guid = nil, key = nil) ⇒ Object

Override the function that creates the raw byte stream for sending so that it generates an XOR key, uses it to scramble the serialized TLV content, and then returns the key plus the scrambled data as the payload.


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# File 'lib/rex/post/meterpreter/packet.rb', line 1305

def to_r(session_guid = nil, key = nil)
  xor_key = (rand(254) + 1).chr + (rand(254) + 1).chr + (rand(254) + 1).chr + (rand(254) + 1).chr

  raw = (session_guid || NULL_GUID).dup
  tlv_data = GroupTlv.instance_method(:to_r).bind(self).call

  if key && key[:key] && (key[:type] == ENC_FLAG_AES128 || key[:type] == ENC_FLAG_AES256)
    # encrypt the data, but not include the length and type
    iv, ciphertext = aes_encrypt(key[:key], tlv_data[HEADER_SIZE..-1])
    # now manually add the length/type/iv/ciphertext
    raw << [key[:type], iv.length + ciphertext.length + HEADER_SIZE, self.type, iv, ciphertext].pack('NNNA*A*')
  else
    raw << [ENC_FLAG_NONE, tlv_data].pack('NA*')
  end

  # return the xor'd result with the key
  xor_key + xor_bytes(xor_key, raw)
end

#xor_bytes(xor_key, bytes) ⇒ Object

Xor a set of bytes with a given XOR key.


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# File 'lib/rex/post/meterpreter/packet.rb', line 1362

def xor_bytes(xor_key, bytes)
  xor_key = xor_key.bytes
  result = ''
  i = 0
  bytes.each_byte do |b|
    result << (b ^ xor_key[i % xor_key.length]).chr
    i += 1
  end
  result
end