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  • CERT Advisory CA-2002-33 Heap Overflow Vulnerability in Microsoft Data Access Components (MDAC)

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Original release date: November 21, 2002
Last revised: --
Source: CERT/CC

A complete revision history can be found at the end of this file.

Systems Affected

All Microsoft Windows systems running the following:

  • Versions of Microsoft Data Access Components (MDAC) prior to 2.7
  • Internet Explorer version 6
  • Internet Explorer version 5.5
  • Internet Explorer version 5.1

Note that Microsoft Windows XP is shipped with MDAC version 2.7 and is not vulnerable by default even though Internet Explorer 6.0 is installed.

Because the normal operation of several applications and web servers on a system depend on the proper operation of the MDAC ActiveX control, other programs could be used as an exploit vector. For example, Internet Information Server may be configured to use MDAC.


A vulnerability in the Microsoft Data Access Components (MDAC) could lead to remote execution of code with the privileges of the current process or user.

I. Description

Microsoft Data Access Components (MDAC) is a collection of utilities and routines to process requests between databases and network applications. A buffer overflow vulnerability exists in the Remote Data Services (RDS) component of MDAC.

The RDS component provides an intermediary step for a client's request for service from a back-end database that enables the web site to apply business logic to the request.

According to Microsoft's Security Bulletin MS02-065, a routine in the RDS component, specifically the RDS Data Stub function, contains an unchecked buffer. The RDS Data Stub function's purpose is to parse incoming HTTP requests and generate RDS commands. This unchecked buffer could be exploited to cause a heap overflow.

There are two ways in which this vulnerability can be exploited. The first involves an attacker sending a malicious HTTP request to a vulnerable service, such as an IIS server. If RDS is enabled, the attacker can execute arbitrary code as the IIS server. RDS is not enabled by default on Windows 2000 and Windows XP systems. It can be disabled on other systems by following the advice in Microsoft's security bulletin.

The other way to exploit this vulnerability involves a malicious web site hosting a page that exploits the buffer overflow in the MDAC RDS stub through a client application, such as Internet Explorer. Most systems running Internet Explorer on operating systems other than Windows XP are vulnerable to this attack. The attacker is able to run arbitrary code as the user viewing the malicious web page.

Both web servers and client applications that rely on MDAC are affected. It is recommended that all users of Microsoft Windows 98, Windows 98 SE, Windows ME, Windows NT 4.0, and Windows 2000 apply the patch (Q329414). Windows XP users are not affected since MDAC 2.7, the non-vulnerable version, is installed by default.

Information about this vulnerability is discussed in VU#542081. This issue is also being referenced as CAN-2002-1142.

II. Impact

A remote attacker could execute arbitrary code with the privileges of the application that processed the request.

In the case of a web server or other service, this is likely to be the SYSTEM or another account with elevated privileges. In the case of a client application, this will be the account used to view the web page.

III. Solution

Apply a patch from your vendor.

Microsoft has released a patch (Q329414) and a security bulletin (MS02-065) to address this issue. An end-user version of MS02-065 is available at

According to the Microsoft advisory, a scenario exists in by which a vulnerable version of the control may be re-installed on a Windows system even after the patch has been applied. This is due to the fact that the vulnerable ActiveX control is signed by Microsoft and the patch does not set the kill bit for the MDAC control.

This vulnerability was reported in an advisory by Foundstone and in MS02-065 by Microsoft.

Feedback can be sent to the Authors: Jason A. Rafail, Chad R. Dougherty, and Cory F. Cohen.

Copyright 2002 Carnegie Mellon University.

Revision History

November 21, 2002: Initial release

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