Westpoint Security Advisory

Title:         Microsoft SQLXML ISAPI Overflow and Cross Site Scripting
Risk Rating:    Medium
Software:     Microsoft SQLXML 3.0 / IIS 5.0 / SQLServer 2000
Platforms:    Win2K
Vendor URL:     www.microsoft.com
Author:        Matt Moore <matt@westpoint.ltd.uk>
Date:        12 June 2002
Advisory ID#:    wp-02-0007.txt
CVE#:        CVE-CAN-2002-0186 (XSS) and CVE-CAN-2002-0187 (Overflow)

Overview:
=========
SQLXML allows XML data to be transferred to and from SQL Server, returning
database queries as XML.

SQlXML has two vulnerabilities: a buffer overflow in the SQLXML ISAPI
filter, and a cross site scripting vulnerability.

More complete details on how SQLXML works can be found in Microsoft's
advisory (see below).

Details:
========

Cross Site Scripting
--------------------
Part of the functionality of SQLXML is being able to run SQL queries via a
URL such as:

IIS-server/Northwind?sql=SELECT+contactname,+phone+FROM+Customers+FOR+XML

This will return an XML document containing the query results.

It is possible to specify an extra parameter in the query, 'root', which
returns the data as above, but with a 'root' tag of the xml document as
the user specified.

This feature can be used to perform cross site scripting attacks against
the web application running on the server:

IIS-server/Northwind?sql=SELECT+contactname,+phone+FROM+Customers+FOR+XML&ro 

ot=<SCRIPT>alert(document.domain)</SCRIPT>

Best practice recommends against allowing ad hoc URL queries against a
database.

SQLXML ISAPI Filter Buffer Overflow
-----------------------------------
When making SQL queries using the 'sql=' functionality of SQLXML it is
possible to specify certain parameters which affect the returned XML
(e.g. xsl=). One of these parameters lets you set a content-type.

It's possible to crash IIS by requesting an overly long string in the
?contenttype= parameter. This could also allow arbitrary code to be run
on the server in the context of the SYSTEM account.

A normal request looks like (in this case, a direct sql= query):

IIS-server/demos?sql=select+*+from+Customers+as+Customer+FOR+XML+auto&root=r 

oot&xsl=custtable.xsl&contenttype=text/html

By specifying >240 characters for the content-type parameter it is possible
to make inetinfo.exe crash.

E.g. (using a 'template' file rather than a direct query, in this case):

IIS-Server/Nwind/Template/catalog.xml?contenttype=text/AAAA...AAA

Patch Information:
------------------
Microsoft has released patches and an advisory for the identified issues.

These are available from:

http://www.microsoft.com/technet/treeview/default.asp?url=/technet/security/ 

bulletin/MS02-030.asp

This advisory is available online at:

http://www.westpoint.ltd.uk/advisories/wp-02-0007.txt