-----BEGIN PGP SIGNED MESSAGE-----
AUSCERT External Security Bulletin Redistribution
ESB-2003.0489 -- CERT Advisory CA-2003-14
Buffer Overflow in Microsoft Windows HTML
15 July 2003
AusCERT Security Bulletin Summary
Product: Windows Server 2003
Windows NT 4.0 Terminal Server
Windows NT 4.0
Impact: Execute Arbitrary Code/Commands
Denial of Service
Access Required: Remote
CVE Names: CAN-2003-0469
- --------------------------BEGIN INCLUDED TEXT--------------------
- -----BEGIN PGP SIGNED MESSAGE-----
CERT Advisory CA-2003-14 Buffer Overflow in Microsoft Windows HTML
Original issue date: July 14, 2003
Last revised: --
A complete revision history is at the end of this file.
* Windows 98 and 98 Second Edition (SE)
* Windows NT 4.0 and 4.0 Terminal Server Edition (TSE)
* Windows Millennium Edition (Me)
* Windows 2000
* Windows XP
* Windows Server 2003
A buffer overflow vulnerability exists in a shared HTML conversion
library included in Microsoft Windows. An attacker could exploit this
vulnerability to execute arbitrary code or cause a denial of service.
Microsoft Windows includes a shared HTML conversion library
(html32.cnv). According to Microsoft Security Bulletin MS03-023, "The
HTML converter is an extension which allows applications to convert
HTML data into Rich Text Format (RTF) while maintaining the formatting
and structure of the data as well as the text. The converter also
supports the conversion of RTF data into HTML."
The HTML conversion library contains a buffer overflow vulnerability
that can be triggered by a specially crafted align attribute in an
<HR> element. The library can be loaded by any application on the
system. For example, Internet Explorer (IE) uses the library to handle
HTML data stored in the clipboard. Using script, an attacker can cause
IE to copy a crafted <HR> element into the clipboard and load the
library. The attacker could accomplish this by convincing a victim to
view an HTML web page or HTML email message with IE, Outlook, or
Outlook Express in a zone where Active scripting and Allow paste
operations via script are enabled.
This vulnerability is not limited to IE, Outlook, or Outlook Express.
Any program, including non-Microsoft applications, can use the
vulnerable library and may present other vectors of attack.
Further information is available in VU#823260. Common Vulnerabilities
and Exposures (CVE) refers to this issue as CAN-2003-0469.
An attacker could execute arbitrary code with the privileges of the
process that loaded the HTML conversion library. The attacker could
also crash the process, causing a denial of service.
Apply a patch
Apply the appropriate patch as specified by Microsoft Security
Modify Internet Explorer security zone configuration
Modify one or both of the following IE security zone settings in the
Internet zone and the zone(s) used by Outlook, Outlook Express, and
any other application that uses Internet Explorer or the WebBrowser
ActiveX control to render HTML:
* Set Allow paste operations via script to Disable
* Set Active scripting to Disable
Either of these changes will prevent attacks that depend on scripting
in the IE HTML rendering engine. However, these changes are not
complete solutions, and they do not prevent attacks that use other
Note that disabling Active scripting provides defense against other
attacks that are outside the scope of this document.
Instructions for modifying IE 5 security zone settings can be found in
the CERT/CC Malicious Web Scripts FAQ. In IE 6, the High security zone
setting includes both of these changes.
Appendix A. Vendor Information
This appendix contains information provided by vendors. When vendors
report new information, this section is updated and the changes are
noted in the revision history. If a vendor is not listed below, we
have not received their comments.
Please see Microsoft Security Bulletin MS03-023.
Appendix B. References
* CERT/CC Vulnerability Note VU#823260 -
* Microsoft Security Bulletin MS03-023 -
This vulnerability was publicly reported by Digital Scream.
Feedback can be directed to the author, Art Manion.
This document is available from:
CERT/CC Contact Information
Phone: +1 412-268-7090 (24-hour hotline)
Fax: +1 412-268-6989
CERT Coordination Center
Software Engineering Institute
Carnegie Mellon University
Pittsburgh PA 15213-3890
CERT/CC personnel answer the hotline 08:00-17:00 EST(GMT-5) /
EDT(GMT-4) Monday through Friday; they are on call for emergencies
during other hours, on U.S. holidays, and on weekends.
We strongly urge you to encrypt sensitive information sent by email.
Our public PGP key is available from
If you prefer to use DES, please call the CERT hotline for more
Getting security information
CERT publications and other security information are available from
our web site
To subscribe to the CERT mailing list for advisories and bulletins,
send email to email@example.com. Please include in the body of your
* "CERT" and "CERT Coordination Center" are registered in the U.S.
Patent and Trademark Office.
Any material furnished by Carnegie Mellon University and the Software
Engineering Institute is furnished on an "as is" basis. Carnegie
Mellon University makes no warranties of any kind, either expressed or
implied as to any matter including, but not limited to, warranty of
fitness for a particular purpose or merchantability, exclusivity or
results obtained from use of the material. Carnegie Mellon University
does not make any warranty of any kind with respect to freedom from
patent, trademark, or copyright infringement.
Conditions for use, disclaimers, and sponsorship information
Copyright 2003 Carnegie Mellon University.
July 14, 2003: Initial release
- -----BEGIN PGP SIGNATURE-----
Version: PGP 6.5.8
- -----END PGP SIGNATURE-----
- --------------------------END INCLUDED TEXT--------------------
You have received this e-mail bulletin as a result of your organisation's
registration with AusCERT. The mailing list you are subscribed to is
maintained within your organisation, so if you do not wish to continue
receiving these bulletins you should contact your local IT manager. If
you do not know who that is, please send an email to firstname.lastname@example.org
and we will forward your request to the appropriate person.
This security bulletin is provided as a service to AusCERT's members. As
AusCERT did not write the document quoted above, AusCERT has had no control
over its content. The decision to follow or act on information or advice
contained in this security bulletin is the responsibility of each user or
organisation, and should be considered in accordance with your organisation's
site policies and procedures. AusCERT takes no responsibility for consequences
which may arise from following or acting on information or advice contained in
this security bulletin.
NOTE: This is only the original release of the security bulletin. It may
not be updated when updates to the original are made. If downloading at
a later date, it is recommended that the bulletin is retrieved directly
from the author's website to ensure that the information is still current.
Contact information for the authors of the original document is included
in the Security Bulletin above. If you have any questions or need further
information, please contact them directly.
Previous advisories and external security bulletins can be retrieved from:
If you believe that your computer system has been compromised or attacked in
any way, we encourage you to let us know by completing the secure National IT
Incident Reporting Form at:
Internet Email: email@example.com
Facsimile: (07) 3365 7031
Telephone: (07) 3365 4417 (International: +61 7 3365 4417)
AusCERT personnel answer during Queensland business
hours which are GMT+10:00 (AEST). On call after hours
for member emergencies only.
-----BEGIN PGP SIGNATURE-----
-----END PGP SIGNATURE-----