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Cisco Collaboration Server 5.0: Troubleshooting Security Vulnerability Caused by the HTTP TRACE/TRACK Methods

Document ID: 107523

Updated: Jul 02, 2008

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Introduction

This document addresses the steps to work around the security vulnerability caused by the HTTP TRACE/TRACK methods for products that use Microsoft Internet Information Services (IIS) as the webserver. Cisco Collaboration Server 5.0 uses IIS 5.0 as the webserver and is susceptible to this vulnerability. The solution is to use Microsoft’s URLScan utility to disable the HTTP TRACE/TRACK methods.

Prerequisites

Requirements

Cisco recommends that you have knowledge of these topics:

  • Microsoft Windows 2000 Server

  • Cisco Collaboration Server 5.0

  • Microsoft IIS 5.0

  • Microsoft URLScan utility

Components Used

The information in this document is based on these software and hardware versions:

  • Microsoft Windows 2000

  • Cisco Collaboration Server versions 5.0

  • Microsoft IIS 5 (when using Windows 2000)

  • Microsoft URLScan 2.5

Conventions

Refer to Cisco Technical Tips Conventions for more information on document conventions.

Webserver HTTP TRACE/TRACK Method Support Cross-Site Tracing Vulnerability

A webserver was detected that supports the HTTP TRACE method. This method allows debugging and connection trace analysis for connections from the client to the webserver. Per the HTTP specification, when this method is used, the webserver echoes back the information sent to it by the client unmodified and unfiltered. Microsoft IIS Webserver uses an alias TRACK for this method, and is functionally the same.

A vulnerability related to this method was discovered. A malicious, active component in a web page can send TRACE requests to a webserver that supports this TRACE method. Usually, browser security disallows access to websites outside of the present site's domain. Although unlikely and difficult to achieve, it is possible, in the presence of other browser vulnerabilities, for the active HTML content to make external requests to arbitrary webservers beyond the hosting webserver. Because the chosen webserver then echoes back the client request unfiltered, the response also includes cookie-based or web-based (if logged on) authentication credentials that the browser automatically sent to the specified web application on the specified webserver. The significance of the TRACE capability in this vulnerability is that the active component in the page visited by the victim user has no direct access to this authentication information, but receives it after the target webserver echoes it back as TRACE response. Because this vulnerability exists as a support for a method required by the HTTP protocol specification, most common webservers are vulnerable.

Microsoft IIS: Microsoft released URLScan (http://www.microsoft.com/windows2000/downloads/recommended/urlscan/default.asp leavingcisco.com), which can be used to screen all incoming requests based on customized rulesets. URLScan can be used to sanitize or disable the TRACE requests from the clients. Note that IIS aliases TRACK to TRACE. Therefore, if URLScan is used to specifically block the TRACE method, the TRACK method should also be added to the filter. URLScan uses the urlscan.ini configuration file, usually in \System32\InetSrv\URLScan directory.

In that, there are two sections: AllowVerbs and DenyVerbs. The former is used if the UseAllowVerbs variable is set to 1; otherwise (if set to 0), the DenyVerbs are used. Clearly, either can be used, depending on whether you want a Default-Deny-Explicit-Allow or a Default-Allow-Explicit-Deny policy. In order to disallow TRACE and TRACK methods through URLScan, first remove TRACK, TRACE methods from the AllowVerbs section and add them to the DenyVerbs section. With this, URLScan will disallow all TRACE and TRACK methods, and generate an error page for all requests using that method. In order to enable the changes, restart the World Wide Web Publishing Service from the Services > Control Panel item.

Install and Configure URLScan Utility Version 2.5 to Disable HTTP TRACE/TRACK Method

Complete these steps:

  1. Install URLScan 2.5 in the Cisco Collaboration Server. In order to download URLScan 2.5, refer to this Microsoft website:

    http://microsoft.com/downloads/details.aspx?FamilyId=23D18937-DD7E-4613-9928-7F94EF1C902A&displaylang=en leavingcisco.com

  2. Edit the urlscan.ini property file present in <Windows 2000 Server install drive>:\WINNT\system32\inetsrv\urlscan.

  3. Change the AllowDotinPath property from 0 to 1. By default, URLScan does not allow dots in URLs, and the Cisco Collaboration Server requires this property to be set to 1 (agents will not be able to login if this property is set to 0).

  4. Add the TRACE and TRACK methods under the DenyVerbs section, and change the AllowVerbs property from 1 to 0.

  5. Restart Internet Information Services(IIS)/World Wide Web services from the Services > Control Panel item on the Cisco Collaboration Server.

Related Information

Updated: Jul 02, 2008
Document ID: 107523