Georgi Guninski security advisory #26, 2000



IIS 5.0 cross site scripting vulnerability - using .htw



Systems affected:

IIS 5.0/Windows 2000. Exploited with browser (IE,NC) but the problem is

in the web server.



Risk: Medium

Date: 28 October 2000



Legal Notice:

This Advisory is Copyright (c) 2000 Georgi Guninski. You may distribute

it unmodified. You may not modify it and distribute it or distribute

parts of it without the author's written permission.



Disclaimer:

The opinions expressed in this advisory and program are my own and not

of any company.

The usual standard disclaimer applies, especially the fact that Georgi

Guninski

is not liable for any damages caused by direct or  indirect use of the

information or functionality provided by this advisory or program.

Georgi Guninski, bears no responsibility for content or misuse of this

advisory or program or any derivatives thereof.



Description:



Using specially designed URLs, IIS 5.0 may return user specified content

to the browser.

This poses great security risk, especially if the browser is JavaScript

enabled and the problem is greater in IE.

By clicking on links, just visiting hostile web pages or opening HTML

email the target IIS sever may return user defined malicous active

content.

This is a bug in IIS 5.0, but it affects end users and is exploited with

a browser.

A typical exploit scenario is stealing cookies which may contain

sensitive information.





Details:

The following URL:

----

alert(document.domain)"" target="_new">http://iis5server/null.htw?CiWebHitsFile=/default.htm&CiRestriction=""

----

(URL may be wrapped in mail clients)

executes in the browser javascript provided by "iis5server" but defined

by a (malicous) user.

The URL may be used in a link or a script.

If /default.htm does not exist another document must be specified.





Workaround:

Remove the .htw extension from application mappings.



Vendor status:

Microsoft was notified on 24 October.



Regards,

Georgi Guninski

http://www.guninski.com