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
"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
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 Bulletin MS03-023.
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:
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
Set Allow paste operations via script to Disable
Set Active scripting to Disable
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
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
This vulnerability was publicly reported by Digital Scream.
Feedback can be directed to the author, Art Manion.
Copyright 2003 Carnegie Mellon University.
July 14, 2003: Initial release