From: maninder.bharadwaj at digital.com (Bharadwaj, Maninder)
Subject: Buffer Overrun in SmartHTML Interpreter Could Allow Code Executio
 n (Q324096)

  


Buffer Overrun in SmartHTML Interpreter Could Allow Code Execution (Q324096)


Originally posted: September 25, 2002


Summary


Who should read this bulletin: Web site administrators using Microsoft?
FrontPage Server Extensions 

Impact of vulnerability: Buffer overrun or denial of service 

Maximum Severity Rating: Critical 

Recommendation: Web site administrators should apply the patch or ensure
that the SmartHTML Interpreter is not available on the server. 

Affected Software: 

*	Microsoft FrontPage Server Extensions 2000 
*	Microsoft FrontPage Server Extensions 2002 
*	Microsoft Windows 2000 (shipped FPSE 2000) 
*	Microsoft Windows XP (shipped FPSE 2000) 

Technical details 

Technical description: 



The SmartHTML Interpreter (shtml.dll) is part of the FrontPage Server
Extensions (FPSE), and provides support for web forms and other
FrontPage-based dynamic content. The interpreter contains a flaw that could
be exposed when processing a request for a particular type of web file, if
the request had certain specific characteristics. This flaw affects the two
versions of FrontPage Server Extensions differently. On FrontPage Server
Extensions 2000, such a request would cause the interpreter to consume most
or all CPU availability until the web service was restarted. An attacker
could use this vulnerability to conduct a denial of service attack against
an affected web server. On FrontPage Server Extensions 2002, the same type
of request could cause a buffer overrun, potentially allowing an attacker to
run code of his choice. 

Mitigating factors: 

*	The IIS
<http://www.microsoft.com/technet/security/tools/locktool.asp> Lockdown
Tool, if used to configure a static web server, disables the SmartHTML
Interpreter. Servers on which this has been done could not be affected by
the vulnerability. 
*	FrontPage Server Extensions install on IIS 4.0, 5.0 and 5.1 by
default, but can be uninstalled if desired. Servers on which this has been
done could not be affected by the vulnerability. 

Severity Rating: 

	Internet Servers	 Intranet Servers	 Client Systems	
FrontPage Server Extensions 2000	 Critical	 Moderate
None	
FrontPage Server Extensions 2002	 Critical	 Moderate
None	
The above assessment
<http://www.microsoft.com/technet/security/topics/rating.asp>  is based on
the types of systems affected by the vulnerability, their typical deployment
patterns, and the effect that exploiting the vulnerability would have on
them. 

Vulnerability identifier: CAN-2002-0692
<http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2002-0692>  

Tested Versions:
Microsoft tested FrontPage Server Extensions 2000 and 2002 to assess whether
they are affected by these vulnerabilities. Previous versions are no longer
supported <http://support.microsoft.com/directory/discontinue.asp> , and may
or may not be affected by these vulnerabilities.

Frequently asked questions 

What's the scope of the vulnerability?

This is a denial
<http://www.microsoft.com/technet/security/bulletin/glossary.asp> of service
and buffer overrun vulnerability. It affects FrontPage Server Extensions
2000 and 2002 differently. With FrontPage Server Extensions 2000, the flaw
could cause most CPU availability to be consumed until the web service is
restarted. An attacker could use this vulnerability to conduct a denial of
service attack against an affected web server. With FrontPage Server
Extensions 2002, the same flaw in the interpreter causes a buffer overrun,
potentially allowing an attacker to run code of the his choice. 

Web site administrators who have used the IIS
<http://www.microsoft.com/technet/security/tools/locktool.asp> Lockdown Tool
to configure their servers as static web servers are already protected
against attacks that would attempt to exploit the vulnerability. 

What causes the vulnerability?

The vulnerability results because of a flaw in the FrontPage Server
Extensions SmartHTML interpreter. The interpreter can enter a mode in which
it consumes all CPU availability on a web server using FrontPage Server
Extensions 2000 or can result in a buffer overrun in FrontPage Server
Extensions 2002, if it receives a request for a particular type of web file,
along with some specific parameters.

What are the FrontPage Server Extensions?

FrontPage
<http://msdn.microsoft.com/library/en-us/dnservext/html/fpovrw.asp> Server
Extensions (FPSE) is a set of tools that can be installed on a
FrontPage-based web site. They serve two basic functions: to allow
authorized personnel to manage the server, add or change content, and
perform other tasks; and to add functions that are frequently used by web
pages, such as search and forms support. 

FPSE installs by default as part of IIS 4.0, 5.0 and 5.1. However, it can be
uninstalled if desired. Microsoft has long recommended that web
administrators uninstall FPSE if not needed. 

What is the SmartHTML interpreter?

The SmartHTML interpreter, shtml.dll, is part of FPSE, and supports certain
types of dynamic web content. For instance, using SmartHTML, a web developer
can build a web page that relies on FrontPage features, but not actually
have those features embedded within the page until a user requests it.

For example, a web developer might want to embed the current date and time
in a web page. In order to do that, the developer might use one of the
WebBot components that come with FrontPage. A WebBot component gives an
author CGI capabilities without writing CGI applications. The web page
author inserts a WebBot into an HTML page. What actually gets inserted is a
specially formatted HTML comment. A WebBot comment looks like a standard
HTML comment with special notation that identifies the WebBot and its
properties. You set the property values from a dialog box when the WebBot
gets inserted. Each WebBot has its own dialog. Microsoft calls the WebBot
notation SmartHTML, and HTML pages containing them SmartHTML pages. 

A WebBot is "executed" when the FrontPage Editor saves the HTML page. A
FrontPage Server Extension app scans the page for embedded WebBot components
and replaces them with standard HTML text. As a result of this scanning
process, a new page is created containing the standard HTML text generated
from the WebBot components and the web visitor sees the date and time
rendered on the web page.

What's wrong with the SmartHTML interpreter?

If a request for a certain type of web file is made in a particular way, it
could have the effect on a web server using FrontPage Server Extensions 2000
of causing the SmartHTML interpreter to cycle endlessly, consuming all of
the server's CPU availability and preventing the server from performing
useful work. On a web server using FrontPage Server Extensions 2002, this
same type of request could have the effect of causing a buffer overrun and
potentially allowing an attacker to run malicious code on that server.

What could an attacker do via this vulnerability?

In the case of FrontPage Server Extensions 2000, an attacker could use this
vulnerability to monopolize a server and prevent legitimate users from being
able to use the web server. In the case of FrontPage Server Extensions 2002,
an attacker could potentially cause a buffer overrun on the web server.

How might an attacker exploit the vulnerability?

The attack itself would only require that the attacker levy a particular
type of request on the SmartHTML interpreter. Upon attempting to process the
request (in the case of FrontPage Server Extensions 2000), the interpreter
would begin to "freewheel", and would continue to do so until the
administrator stopped and restarted the web service. In some cases, it might
be necessary to reboot the system in order to do this. In the case of
FrontPage Server Extensions 2002, the request could cause a buffer overrun
in the interpreter and allow code of the attacker's choice to run in the
context of the interpreter.

If an attacker exploited the buffer overrun in FrontPage Server Extensions
2002, in what context would the hostile code run?

In the case of the buffer overrun in FrontPage Server Extensions 2002, the
malicious code would run as system, even though getting to system would take
a convoluted exploit. Nonetheless, it is possible to that an attacker could
create such an exploit and be running as system.

What steps could an administrator take to protect against the vulnerability?

Of course, the simplest way to eliminate the vulnerability is to install the
patch. But even if the patch were not installed, a server wouldn't be at
risk if FPSE had been uninstalled, or if the SmartHTML interpreter were not
in use. For instance, the IIS
<http://www.microsoft.com/technet/security/tools/locktool.asp> Lockdown
Tool, if used to configure a static web server, disables the interpreter.

How does the patch eliminate the vulnerability?

The patch causes the SmartHTML interpreter to reject the requests at issue
here, as they aren't valid requests.






























































Patch availability


Download locations for this patch 

*	Microsoft FrontPage Server Extensions 2002 for all platforms
http://download.microsoft.com/download/FrontPage2002/fpse1002/1/W98NT42KMeXP
/EN-US/fpse1002.exe
<http://download.microsoft.com/download/FrontPage2002/fpse1002/1/W98NT42KMeX
P/EN-US/fpse1002.exe>  
*	Microsoft FrontPage Server Extension 2000 for NT4
http://download.microsoft.com/download/fp2000fd2000/Patch/1/W9XNT4Me/EN-US/f
pse0901.exe
<http://download.microsoft.com/download/fp2000fd2000/Patch/1/W9XNT4Me/EN-US/
fpse0901.exe>  
*	Microsoft FrontPage Server Extensions 2000 for Windows XP 


*	http://www.microsoft.com/downloads/release.asp?ReleaseID=42995
<http://www.microsoft.com/downloads/release.asp?ReleaseID=42995>  
*	Windows Update <http://windowsupdate.microsoft.com/>  

*	Microsoft FrontPage Server Extensions 2000 for Windows 2000 


*	http://www.microsoft.com/downloads/release.asp?ReleaseID=42954
<http://www.microsoft.com/downloads/release.asp?ReleaseID=42954>  
*	Windows Update <http://windowsupdate.microsoft.com/>  

Additional information about this patch 

Installation platforms: 
This patch can be installed on: 

*	FrontPage Server Extensions 2002: The patch can be applied on all
platforms which support FrontPage Server Extensions 2002. 
*	FrontPage Server Extensions 2000: The patches can be applied on the
following systems running FrontPage Server Extensions 2000 - Windows XP,
Windows 2000, and NT4. 

Inclusion in future service packs:
The fix for this issue will be included in Windows 2000 SP4, Windows XP SP2
and any future service packs for FPSE 2002. 

Reboot needed: Yes 

Patch can be uninstalled:


*	FrontPage Server Extensions 2000 patches on Windows 2000 and Windows
XP can be uninstalled. 
*	FrontPage Server Extensions 2000 patches for NT4 cannot be
uninstalled. 
*	FrontPage Server Extensions 2002 patches cannot be uninstalled. 

Superseded patches: None. 

Verifying patch installation: 

*	Users who are applying the patch on Windows 2000 or Windows XP
should refer to Q324096
<http://support.microsoft.com/default.aspx?scid=kb;en-us;Q324096>  
*	Users who are applying the patch for FrontPage Server Extensions
2000 please refer to Knoweldege Base article Q329085
<http://support.microsoft.com/default.aspx?scid=kb;en-us;Q329085>  
*	Users who are applying the patch for FrontPage Server Extensions
2002 please refer to Knoweldege Base article Q329086
<http://support.microsoft.com/default.aspx?scid=kb;en-us;Q329086>  

Caveats:
Users running FrontPage Server Extensions 2002 on any supported platform who
have not applied the latest update will need to apply the update before
installing this patch. To learn more about the update, please read Q317296
<http://support.microsoft.com/default.aspx?scid=kb;en-us;Q317296> . To go
directly to the FrontPage Server Extensions 2002 Update, click here
<http://download.microsoft.com/download/FrontPage2002/fpse1001/1/W98NT42KMeX
P/EN-US/fpse1001.exe> . 

Localization:
Localized versions of this patch are available at the locations discussed in
"Patch Availability". 

Obtaining other security patches: 
Patches for other security issues are available from the following
locations: 

*	Security patches are available from the Microsoft
<http://www.microsoft.com/downloads/search.asp?Search=Keyword&Value=%27secur
ity_patch%27&OpSysID=1> Download Center, and can be most easily found by
doing a keyword search for "security_patch". 
*	Patches for consumer platforms are available from the WindowsUpdate
<http://windowsupdate.microsoft.com/>  web site 


Other information: 


Acknowledgments 

Microsoft thanks
<http://www.microsoft.com/technet/security/bulletin/policy.asp>  Maninder
Bharadwaj of Digital Defense Services part of Digital GlobalSoft Ltd. for
reporting this issue to us and working with us to protect customers. 

Support: 

*	Microsoft Knowledge Base article Q324096 discusses this issue and
will be available approximately 24 hours after the release of this bulletin.
Knowledge Base articles can be found on the Microsoft Online
<http://support.microsoft.com/?scid=fh;en-us;kbhowto> Support web site. 
*	Technical support is available from Microsoft
<http://support.microsoft.com/directory/question.asp?sd=gn&fr=0> Product
Support Services. There is no charge for support calls associated with
security patches. 

Security Resources: The Microsoft TechNet
<http://www.microsoft.com/technet/security/default.asp> Security Web Site
provides additional information about security in Microsoft products. 

Exploit: 
The exploit could be provided for research and educational purposes on
request. 

Regards,

-------------------------------------------------
Maninder Bharadwaj
Senior Security Specialist- Digital Defense Services
Digital GlobalSoft Ltd.
(A subsidiary of Hewlett-Packard Co., USA)
Digital Park, Plot No. 39/40, Electronic City
Hosur Road, Bangalore - 561 229
-------------------------------------------------
Tel: +91 80 8528395 Ext 12171
Fax: +91 80 8528420
Email: maninder.bharadwaj@...ital.com
Web:  www.digitalglobalsoft.com


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