Adding FTP Deny URL Sequences <add>

Overview

The <add> element of the <denyUrlSequences> collection specifies a unique sequence of characters to add to the collection of denied URL sequences for FTP 7.

Note: When request filtering blocks an FTP request because of a denied URL sequence, FTP 7 will return an FTP error to the client and log the following FTP substatus that identifies the reason that the request was denied:

FTP Substatus Description
9 Denied URL sequence detected in the requested path.

This substatus allows Web administrators to analyze their IIS logs and identify potential threats.

Compatibility

Version Notes
IIS 7.5 The <add> element of the <denyUrlSequences> element ships as a feature of IIS 7.5.
IIS 7.0 The <add> element of the <denyUrlSequences> element was introduced in FTP 7.0, which was a separate download for IIS 7.0.
IIS 6.0 The FTP service in IIS 6.0 did not support request filtering.

Note: The FTP 7.0 and FTP 7.5 services shipped out-of-band for IIS 7.0, which required downloading and installing the modules from the following URL:

http://www.iis.net/expand/FTP

With Windows 7 and Windows Server 2008 R2, the FTP 7.5 service ships as a feature for IIS 7.5, so downloading the FTP service is no longer necessary.

Setup

To support FTP publishing for your Web server, you must install the FTP service. To do so, use the following steps.

IIS 7.5 for Windows Server 2008 R2

  1. On the taskbar, click Start, point to Administrative Tools, and then click Server Manager.
  2. In the Server Manager hierarchy pane, expand Roles, and then click Web Server (IIS).
  3. In the Web Server (IIS) pane, scroll to the Role Services section, and then click Add Role Services.
  4. On the Select Role Services page of the Add Role Services Wizard, expand FTP Server.
  5. Select FTP Service.

    Note: To support ASP.Membership authentication or IIS Manager authentication for the FTP service, you will also need to select FTP Extensibility.
  6. Click Next.
  7. On the Confirm Installation Selections page, click Install.
  8. On the Results page, click Close.

IIS 7.5 for Windows 7

  1. On the taskbar, click Start, and then click Control Panel.
  2. In Control Panel, click Programs and Features, and then click Turn Windows Features on or off.
  3. Expand Internet Information Services, and then FTP Server.
  4. Select FTP Service.

    Note: To support ASP.Membership authentication or IIS Manager authentication for the FTP service, you will also need to select FTP Extensibility.
  5. Click OK.

IIS 7.0 for Windows Server 2008 and Windows Vista

  1. Download the installation package from the following URL:
  2. Follow the instructions in the following walkthrough to install the FTP service:

How To

Note: FTP Request Filtering did not have a user interface in the FTP 7.0 release; the FTP Request Filtering UI was added in the FTP 7.5 release.

How to deny an FTP URL sequence

  1. Open Internet Information Services (IIS) Manager:
    • If you are using Windows Server 2008 or Windows Server 2008 R2:
      • On the taskbar, click Start, point to Administrative Tools, and then click Internet Information Services (IIS) Manager.
    • If you are using Windows Vista or Windows 7:
      • On the taskbar, click Start, and then click Control Panel.
      • Double-click Administrative Tools, and then double-click Internet Information Services (IIS) Manager.
  2. In the Connections pane, go to the site or directory for which you want to modify your request filtering settings.
  3. In the Home pane, double-click FTP Request Filtering.
  4. In the FTP Request Filtering pane, click the Denied URL Sequences tab.
  5. Click Add URL Sequence... in the Actions pane.
  6. In the Add Deny Sequence dialog box, enter the URL sequence that you wish to block.
  7. Click OK.

Configuration

The <add> element of the <denyUrlSequences> collection is configured at the global, site or URL level.

Attributes

Attribute Description
sequence Required string attribute.

Specifies sequences of characters in URLs that the FTP server should never process to help prevent URL-based attacks on the FTP server.

Child Elements

None.

Configuration Sample

The following sample illustrates several security-related configuration settings in the <system.ftpServer> element for an FTP site. More specifically, the <location> settings in this example demonstrate how to:

  • Specify an FTP authorization rule for read and write access for the administrators group.
  • Specify FTP request filtering options that deny *.exe, *.bat, and *.cmd files.
  • Specify FTP request limits for a maximum content length of 1000000 bytes and a maximum URL length of 1024 bytes.
  • Block FTP access to the _vti_bin virtual directory, which is used with the FrontPage Server Extensions.
  • Specify FTP IP filtering options that allow access from 127.0.0.1 and deny access from the 169.254.0.0/255.255.0.0 range of IP addresses.
<location path="ftp.example.com">
  <system.ftpServer>
  <security>
    <authorization>
      <add accessType="Allow" roles="administrators" permissions="Read, Write" />
    </authorization>
    <requestFiltering>
      <fileExtensions allowUnlisted="true">
        <add fileExtension=".exe" allowed="false" />
        <add fileExtension=".bat" allowed="false" />
        <add fileExtension=".cmd" allowed="false" />
      </fileExtensions> <requestLimits maxAllowedContentLength="1000000" maxUrl="1024" /> <hiddenSegments> <add segment="_vti_bin" /> </hiddenSegments>
    </requestFiltering>
<ipSecurity enableReverseDns="false" allowUnlisted="true">
<add ipAddress="127.0.0.1" allowed="true" />
<add ipAddress="169.254.0.0" subnetMask="255.255.0.0" allowed="false" />
</ipSecurity>
  </security>
  </system.ftpServer>
</location>

Sample Code

The following examples will deny the URL sequence "bin" for FTP, which will prevent access to the "bin", "_vti_bin", or "cgi-bin" paths, and also prevent uploading files with a file name extension of ".bin."

AppCmd.exe

appcmd.exe set config "Default Web Site" -section:system.ftpServer/security/requestFiltering /+"denyUrlSequences.[sequence='bin']" /commit:apphost

Note: You must be sure to set the commit parameter to apphost when you use AppCmd.exe to configure these settings. This commits the configuration settings to the appropriate location section in the ApplicationHost.config file.

C#

using System;
using System.Text;
using Microsoft.Web.Administration;
internal static class Sample { private static void Main() { using (ServerManager serverManager = new ServerManager()) { Configuration config = serverManager.GetApplicationHostConfiguration(); ConfigurationSection requestFilteringSection = config.GetSection("system.ftpServer/security/requestFiltering", "Default Web Site"); ConfigurationElementCollection denyUrlSequencesCollection = requestFilteringSection.GetCollection("denyUrlSequences"); ConfigurationElement addElement = denyUrlSequencesCollection.CreateElement("add"); addElement["sequence"] = @"bin"; denyUrlSequencesCollection.Add(addElement); serverManager.CommitChanges(); } } }

VB.NET

Imports System
Imports System.Text
Imports Microsoft.Web.Administration
Module Sample Sub Main() Dim serverManager As ServerManager = New ServerManager Dim config As Configuration = serverManager.GetApplicationHostConfiguration Dim requestFilteringSection As ConfigurationSection = config.GetSection("system.ftpServer/security/requestFiltering", "Default Web Site") Dim denyUrlSequencesCollection As ConfigurationElementCollection = requestFilteringSection.GetCollection("denyUrlSequences") Dim addElement As ConfigurationElement = denyUrlSequencesCollection.CreateElement("add") addElement("sequence") = "bin" denyUrlSequencesCollection.Add(addElement) serverManager.CommitChanges() End Sub End Module

JavaScript

var adminManager = new ActiveXObject('Microsoft.ApplicationHost.WritableAdminManager');
adminManager.CommitPath = "MACHINE/WEBROOT/APPHOST";
var requestFilteringSection = adminManager.GetAdminSection("system.ftpServer/security/requestFiltering", "MACHINE/WEBROOT/APPHOST/Default Web Site");
var denyUrlSequencesCollection = requestFilteringSection.ChildElements.Item("denyUrlSequences").Collection;

var addElement = denyUrlSequencesCollection.CreateNewElement("add");
addElement.Properties.Item("sequence").Value = "bin";
denyUrlSequencesCollection.AddElement(addElement);

adminManager.CommitChanges();

VBScript

Set adminManager = createObject("Microsoft.ApplicationHost.WritableAdminManager")
adminManager.CommitPath = "MACHINE/WEBROOT/APPHOST"
Set requestFilteringSection = adminManager.GetAdminSection("system.ftpServer/security/requestFiltering", "MACHINE/WEBROOT/APPHOST/Default Web Site")
Set denyUrlSequencesCollection = requestFilteringSection.ChildElements.Item("denyUrlSequences").Collection

Set addElement = denyUrlSequencesCollection.CreateNewElement("add")
addElement.Properties.Item("sequence").Value = "bin"
denyUrlSequencesCollection.AddElement(addElement)

adminManager.CommitChanges()
Deprecated Elements