Prevent brute force attacks in Microsoft FTP Server (IIS6/7)

See this post from the IIS newsgroup for some code to resolve the issue

Also below is Chrissy Lemaire's script

'****************************************************************************
' This script created by Chrissy LeMaire ([email protected])
' Website: http://netnerds.net/
'
' NO WARRANTIES, etc.
'
' This script instantly bans IP addresses trying to login to FTP
' using the NT account "Administrator"
'
' Run this script on the FTP server. It sits in the back and waits for an 
' event viewer "push" that lets it know someone failed FTP authentication.
'
' This script has only been tested on Windows Server 2003. It assumes, as it 
' should, that there are no legitimate Administrator account FTP logins.
'
' "What it does"
' 1. Sets an Async Event Sink to notify the script when someone fails MS-FTP auth
' 2. When alerted, the script parses the last day's FTP logs for all FTP sites (this
'    is because the Event Viewer doesn't tell you which FTP site, if you have more than
'    one, is the one getting hit)
' 3. Compiles the list of IPs to be banned and then bans them using IIS /and/
'    IP level banning (thanks Spencer @ netortech.com for the idea)
'*****************************************************************************

' Push Event Viewer Alert
    Set objWMIService = GetObject("winmgmts:{(security)}!root/cimv2")
    Set eventSink = wscript.CreateObject("WbemScripting.SWbemSink", "EVSINK_")
    strWQL = "Select * from __InstanceCreationEvent where TargetInstance isa  'Win32_NTLogEvent' and TargetInstance.SourceName = 'MSFTPSVC' and TargetInstance.EventCode = 100"
    objWMIService.ExecNotificationQueryAsync eventSink,strWQL

' Keep it going forever
While (True)
    Wscript.Sleep(1000)
Wend

Sub EVSINK_OnObjectReady(objObject, objAsyncContext)
  If InStr(LCase(objObject.TargetInstance.Message),"administrator") > 0 Then 
    Set objFTPSVC = GetObject("IIS://localhost/MSFTPSVC")
    Set WshShell = CreateObject("WScript.Shell")
    Set objFSO = CreateObject("Scripting.FileSystemObject")
    Set objLog = CreateObject("MSWC.IISLog")
    Set objDictionary = CreateObject("Scripting.Dictionary")
    Set objFTPIPSec = objFTPSVC.IPSecurity

    'Get IP address of server so we can use it later to give the offending IP a bad route
    Set IPConfigSet = GetObject("winmgmts:\\.\root\cimv2").ExecQuery("SELECT * FROM Win32_NetworkAdapterConfiguration WHERE IPEnabled=TRUE")
    for each IPConfig in IPConfigSet
      if Not IsNull(IPConfig.DefaultIPGateway) then serverIP =  IPConfig.IPAddress(0)
    Next
    Set IPConfigSet = Nothing

    'Iterate through each FTP site. See #2 up above.
      For Each objSITE in objFTPSVC
        If lcase(objSITE.class) = "iisftpserver" Then
          ftpLogFilePath =  WshShell.ExpandEnvironmentStrings(objSITE.LogFileDirectory) & "\msftpsvc" & objSITE.Name

          Set objFolder = objFSO.GetFolder(ftpLogFilePath)
            Set objFiles = objFolder.Files
              For Each fileName In objFiles
                lastFile = fileName
              Next
            strLogFile = lastFile
            Set file = Nothing
          Set objFolder = Nothing

          'Use the IIS log file parser provided by MSFT
          objLog.OpenLogFile strLogFile, 1, "MSFTPSVC", 1, 0 
            '(FileName,IOMode,ServiceName,ServiceInstance,OutputLogFileFormat) 
            ' 0 = NotApplicable, 1 = ForReading  
            While NOT objLog.AtEndOfLog
              objLog.ReadLogRecord
              If LCase(objLog.URIStem) = "administrator" Then
                ClientIP = objLog.ClientIP
                  If objDictionary.Exists(ClientIP) = False Then
                      'Kill the route to the machine then add it to the array of banned IPs.
                      Set WshShell = WScript.CreateObject("WScript.Shell")
                    WshShell.Run "ROUTE ADD " & clientIP & " MASK 255.255.255.255 " & serverIP, 1, True
                    Set WshShell = Nothing
                    objDictionary.Add ClientIP, "255.255.255.255" '255 is just there for padding.
                  End If 
              End If
            Wend  
          objLog.CloseLogFiles 1
        End If
      Next

      'Append the newly banned IPs to the currently banned IPs  
      If objDictionary.Count > 0 And objFTPIPSec.GrantByDefault = True Then 
        bannedIPArray = objFTPIPSec.IPDeny
          For i = 0 to ubound(bannedIPArray)
          clientIP = Left(bannedIPArray(i),InStr(bannedIPArray(i),",")-1)
            If objDictionary.Exists(ClientIP) = False Then
              objDictionary.Add bannedIPArray(i), "255.255.255.255"
            End If 
          Next

        objFTPIPSec.IPDeny = objDictionary.Keys
        objFTPSVC.IPSecurity = objFTPIPSec
        objFTPSVC.SetInfo
      End If

    Set objFTPIPSec = Nothing
    Set objDictionary = Nothing
    Set objLog = Nothing
    Set objFSO = Nothing
    Set objFTPSVC = Nothing
  End If
  End Sub

Simply block access to the FTP server to that IP or subnet. Odds are that IP won't ever need legit access to your FTP server.

You can do this in IIS or via your firewall/ACL.

You could change the FTP port.

1. Using Internet Service Manager, set the FTP properties to the desired port.
2. Apply the changes and stop the service.
3. Open the file Services (located in the \System32\Drivers\Etc directory.
4. Find the line ftp 21/tcp, and change it to reflect the new port.
5. Save the file, then run the file Services.exe located in the \System32 directory.
6. Restart the FTP service in Internet Service Manager. (from this thread).

...alternatively, you could install CopSSH, point it to a high port and use SFTP.

If you really need FTP on port 21, check out FileZilla. It has a built-in anti-hammering feature.