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CERT Advisory CA-2000-16 Microsoft 'IE Script'/Access/OBJECT Tag
Vulnerability
Original release date: August 11, 2000
Last revised: --
Source: CERT/CC
A complete revision history is at the end of this file.
Systems Affected
* Internet Explorer 4.x, 5.x
* Microsoft Access 97 or 2000
Overview
Under certain conditions, Internet Explorer can open Microsoft Access
database or project files containing malicious code and execute the
code without giving a user prior warning. Access files that are
referenced by OBJECT tags in HTML documents can allow attackers to
execute arbitrary commands using Visual Basic for Applications (VBA)
or macros.
A patch which protects against all known variants of attack exploiting
this vulnerability is now available. A workaround which was previously
suggested provided protection against one specific publicly-available
exploit using .mdb files but did not protect against attack using many
other Access file types. (See Appendix B for a complete list of file
types.)
I. Description
Last month, a workaround for the "IE Script" vulnerability was
addressed in Microsoft Security Bulletin MS00-049: Subsection
"Workaround for 'The IE Script' Vulnerability." Microsoft has just
re-released MS00-049, which now includes information about a patch for
this vulnerability. The CERT Coordination Center is issuing this
advisory to raise awareness in the Internet community about the need
to apply this patch to protect IE users against all variants of
attacks which can exploit this particular vulnerability.
Initial Findings
Many of the initial public details about the vulnerability were
discussed on the SecurityFocus Bugtraq mailing list, as well as in a
SANS Flash Advisory:
http://www.securityfocus.com/bid/1398
http://www.sans.org/newlook/resources/win_flaw.htm
This vulnerability in IE can be used to open Access data or project
files. (See Appendix B for a complete list of file types.) Visual
Basic for Application (VBA) code embedded within these files will then
execute. If a warning message appears (depending on the security
settings in IE), it will only do so after the code has been run.
Attackers exploit this vulnerability by placing OBJECT tags in HTML
files posted on malicious Web sites or transmitted via email or via
newsgroup postings. The OBJECT tag can look like
<OBJECT data="database.mdb" id="d1"></OBJECT">
Note, however, the file extension does not have to be .mdb; an
attacker may use any of the ones listed in Appendix B.
The Access file can then open before any warning messages are
displayed, regardless of the default security settings in either IE or
Access. Since Access files can contain VBA or macro code executed upon
opening the file, arbitrary code can be run by a remote intruder on a
victim machine without prior warning.
While this is not an ActiveX issue per se, since all Microsoft Office
documents are normally treated like ActiveX controls, by default
Microsoft Access files are treated as unsafe for scripting within the
IE Security Zone model. This vulnerability, however, can be used to
reference an Access file and execute VBA or macro code even if
scripting has been disabled in Internet Explorer.
Other Vulnerable OBJECT tag extensions
In Microsoft Security Bulletin MS00-049, Microsoft initially provided
a workaround for this vulnerability which involved setting the Admin
password in MS Access. However, unlike with Access data files, setting
the Admin password will not protect against exploits using project
files (.ade, .adp). (See Appendix B.)
Because Access project files rely on SQL backends to authenticate
their requests, project files created without SQL content can bypass
the default authentication for such requests in MS Access. For more
information regarding Access project files, see
http://msdn.microsoft.com/library/techart/acaccessprojects.htm
II. Impact
A remote intruder can send malicious HTML via an email message,
newsgroup posting, or downloaded Web page and may be able to execute
arbitrary code on a victim machine.
III. Solution
Apply the patch provided by Microsoft
Microsoft has released the following patch which addresses the "IE
Script" vulnerability, as well as others:
http://www.microsoft.com/windows/ie/download/critical/patch11.htm
Please see MS00-055 "Patch Available for 'Scriptlet Rendering'
Vulnerability" for additional information regarding other issues
addressed by this patch:
http://www.microsoft.com/technet/security/bulletin/ms00-055.asp
Note that the OBJECT tag issues addressed by MS00-049, MS00-055, and
this advisory are separate from those addressed by the recently
released MS00-056: "Patch Available for 'Microsoft Office HTML Object
Tag' Vulnerability."
Microsoft's initial workaround for this issue was for users to set the
Admin password for Access. Since Access does not allow a user to
disable VBA code embedded in Access data and project files, the CERT
Coordination Center recommends that users follow the suggested
workaround and set the Admin password even after the patch for this
vulnerability has been applied.
Appendix A contains information provided by vendors for this advisory.
We will update the appendix as we receive more information. If you do
not see your vendor's name, the CERT/CC did not hear from that vendor.
Please contact your vendor directly.
Appendix A. Vendor Information
Microsoft Corporation
Microsoft has published the following documents regarding this issue:
http://www.microsoft.com/technet/security/bulletin/ms00-049.asp
http://www.microsoft.com/technet/security/bulletin/fq00-049.asp
http://www.microsoft.com/technet/support/kb.asp?ID=269368
Appendix B. Additional Information
The full list of OBJECT tag extensions which may be used to exploit
this vulnerability is listed below:
* .adp - Microsoft Access project file
* .ade - ADP file with all modules compiled and all editable source
code removed
* .mdb - Microsoft Access database file
* .mde - MDB file with all modules compiled and all editable source
code removed
* .mda - Microsoft Access VBA add-in
* .mdw - Microsoft Access workgroup information file synonym for
the system database used to store group and user account
names and the passwords used to authenticate users when
they log on to an Access database or MDE file secured
with user-level security
The patch provided by Microsoft addresses all the file extensions
identified above.
Please consult the following resources for further information
regarding the other file types involved in exploited this
vulnerability:
* http://www.microsoft.com/office/ork/2000/appndx/glossary.htm#adefile
* http://www.microsoft.com/office/ork/2000/appndx/glossary.htm#adpfile
* http://msdn.microsoft.com/library/officedev/off2000/defAddIn.htm
* http://www.microsoft.com/office/ork/2000/appndx/glossary.htm#mdbfile
* http://www.microsoft.com/office/ork/2000/appndx/glossary.htm#mdefile
* http://www.microsoft.com/office/ork/2000/appndx/glossary.htm#workgroupinformationfile
_____________________________________________________________
The CERT Coordination Center thanks Timothy Mullen, Alan Paller
and the SANS Research Office, and the Microsoft Security Response
Center for their help in developing this advisory.
_____________________________________________________________
Author: Jeffrey S. Havrilla
__________________________________________________________________
This document is available from:
http://www.cert.org/advisories/CA-2000-16.html
__________________________________________________________________
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Revision History
August 11, 2000: Initial release
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