Scripts can be run in the error page that is returned by ISA Server

If you click a link (or URL) to a page that includes script code that for any reason generates an error, the error message from Internet Security and Acceleration (ISA) Server contains the original script from the link and it runs in your Web browser.

This is a cross-site scripting vulnerability that affects the error page that ISA Server generates in response to a request for a non-existent page or an unsuccessful connection attempt to a page. As with all cross-site scripting vulnerabilities, this vulnerability could enable an attacker to either run script in the security domain of another, presumably trusted, Web site, or to access cookies that a site had written to a your computer.

This problem occurs because ISA Server returns the complete original requested URL to the browser in the error message along with the description of the reason why the URL could not be accessed. Because the original request contains a script, the browser runs the script on receipt.

The fix corrects the problem by not returning the URLLOCATION token in the error that is returned to the browser. The Web Proxy service has a list of templates for the error pages. In these templates, there are places for tokens that the service populates before returning the page to the client. One of those tokens is URLLOCATION, which contains the URL. In the template it appears as: The page that is returned to the client appears as: ISA Server supports editing of the error pages. Administrators can change the text and format of these error pages and use the tokens as they want in the pages; the Web Proxy service returns the pages accordingly.

This fix stops the support for the URLLOCATION token. ISA Server ignores the token in the generic error pages or in pages that administrators have edited. ISA Server also removes the "URL" prefix before this token. This change will be in effect for all ISA Server versions in all languages.

Service Pack Information

This problem was first corrected in Microsoft Internet Security and Acceleration Server 2000 Service Pack 1.
For additional information about how to obtain the latest ISA Server service pack, click the following article number to view the article in the Microsoft Knowledge Base:

Hotfix information

A supported hotfix is available from Microsoft. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing this specific problem.

If the hotfix is available for download, there is a "Hotfix download available" section at the top of this Knowledge Base article. If this section does not appear, submit a request to Microsoft Customer Service and Support to obtain the hotfix.

Note If additional issues occur or if any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, visit the following Microsoft Web site: Note The "Hotfix download available" form displays the languages for which the hotfix is available. If you do not see your language, it is because a hotfix is not available for that language.The English version of this hotfix has the file attributes (or later) that are listed in the following table. The dates and times for these files are listed in coordinated universal time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time tool in Control Panel.

Microsoft has confirmed that this problem may cause a degree of security vulnerability in Microsoft Internet Security and Acceleration (ISA) Server 2000.

For more information about this vulnerability, see the following Microsoft Web site: Cross-site scripting is a type of security vulnerability that results when Web content does not adequately filter its inputs. In most cases, cross-site scripting occurs when a Web page accepts some kind of user input (for example, a phrase to search for) and then creates a page using that input. If the page does not check for the presence of script within the input, the script, when it is processed as part of the Web page, runs within the Web site's domain.

Such a condition is not dangerous when you provide the input (you could have performed the actions directly rather than performing them via the script). However, there are cases in which it is possible for a third party to "inject" input that contains script into your Web session. This does pose a hazard because it could enable the third party's script to run in your browser by using the security settings appropriate to the Web page. For additional information, see the following Microsoft Web site: The fix that is described in this article also applies to the following Microsoft Knowledge Base article: