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  Microsoft Visual Basic for Applications buffer overflow

From:MICROSOFT <secure_(at)_microsoft.com>
Date:08.08.2006
Subject:Microsoft Security Bulletin MS06-047 Vulnerability in Microsoft Visual Basic for Applications Could Allow Remote Code Execution (921645)

Microsoft Security Bulletin MS06-047
Vulnerability in Microsoft Visual Basic for Applications Could Allow Remote Code Execution (921645)
Published: August 8, 2006

Version: 1.0
Summary

Who Should Read this Document: Customers using Microsoft Office applications or applications that use Microsoft Visual Basic for Applications.

Impact of Vulnerability: Remote Code Execution

Maximum Severity Rating: Critical

Recommendation: Customers should apply the update immediately

Security Update Replacement: This bulletin replaces a prior security update. See the frequently asked questions (FAQ) section of this bulletin for the complete list.

Caveats: None

Tested Software and Security Update Download Locations:

Affected Software:


Microsoft Office 2000 Service Pack 3 — Download the update (KB920822)


Microsoft Project 2000 Service Release 1 — Download the update (KB920822)


Microsoft Access 2000 Runtime Service Pack 3 — Download the update (KB920822)


Microsoft Office XP Service Pack 3 — Download the update (KB920821)


Microsoft Project 2002 Service Pack 1 — Download the update (KB920821)


Microsoft Visio 2002 Service Pack 2 — Download the update (KB920821)


Microsoft Works Suites:


Microsoft Works Suite 2004 — Download the update (KB920821) (same as the Microsoft Office XP update)


Microsoft Works Suite 2005 — Download the update (KB920821) (same as the Microsoft Office XP update)


Microsoft Works Suite 2006 — Download the update (KB920821) (same as the Microsoft Office XP update)


Microsoft Visual Basic for Applications SDK 6.0 — Download the update (KB923167)


Microsoft Visual Basic for Applications SDK 6.2 — Download the update (KB923167)


Microsoft Visual Basic for Applications SDK 6.3 — Download the update (KB923167)


Microsoft Visual Basic for Applications SDK 6.4 — Download the update (KB923167)

Non-Affected Software:


Microsoft Office 2003 Service Pack 1 and Microsoft Office 2003 Service Pack 2

The software in this list has been tested to determine whether the versions are affected. Other versions either no longer include security update support or may not be affected. To determine the support life cycle for your product and version, visit the Microsoft Support Lifecycle Web site.
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General Information

Executive Summary

Executive Summary:

This update resolves a newly discovered, privately reported vulnerability. The vulnerability is documented in the "Vulnerability Details" section of this bulletin.

On vulnerable versions of Office or Microsoft Visual Basic for Applications, if a user is logged on with administrative user rights, an attacker who successfully exploited this vulnerability could take complete control of an affected system. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights.

We recommend that customers apply the update immediately.

Severity Ratings and Vulnerability Identifiers:
Vulnerability Identifiers Impact of Vulnerability Microsoft Office 2000 Microsoft Office XP Microsoft Visual Basic for Applications SDK 6.0, 6.2, 6.3 and 6.4

Visual Basic for Applications Vulnerability - CVE-2006-3649


Remote Code Execution


Critical


Important


Important

Note The severity ratings for Microsoft Works Suite maps to the Microsoft Office versions as follows:


The Microsoft Works Suite 2004, 2005, and 2006 severity rating is the same as the Microsoft Office XP severity rating.

This assessment is based on the types of systems that are affected by the vulnerability, their typical deployment patterns, and the effect that exploiting the vulnerability would have on them.
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Frequently Asked Questions (FAQ) Related to This Security Update

What updates does this release replace?
This security update replaces a prior security update. The security bulletin ID and affected operating systems are listed in the following table.
Bulletin ID Microsoft Office 2000, Project 2000 Service Release 1, and Access 2000 Runtime Service Pack 3 Microsoft Office XP, Project 2002 Service Pack 1, and Visio 2002 Service Pack 2 Microsoft Visual Basic for Applications SDK 6.0, 6.2, and 6.3 Microsoft Visual Basic for Applications SDK 6.4

MS03-037


Replaced


Not applicable


Replaced


Not applicable

Can I use the Microsoft Baseline Security Analyzer (MBSA) to determine whether this update is required?

The following table provides the MBSA detection summary for this security update.
Product MBSA 1.2.1 MBSA 2.0

Microsoft Office 2000


Yes


No

Microsoft Office XP


Yes


Yes

Note MBSA 1.2.1 uses an integrated version of the Office Detection Tool (ODT) which does not support remote scans of this security update. For more information about MBSA, visit the MBSA Web site.

Note MSBA does not support Microsoft Visual Basic for Applications SDK 6.0, 6.2, 6.3 and 6.4.

For more information about MBSA, visit the MBSA Web site. For more information about the programs that Microsoft Update and MBSA 2.0 currently do not detect, see Microsoft Knowledge Base Article 895660.

Can I use Systems Management Server (SMS) to determine whether this update is required?
The following table provides the SMS detection summary for this security update.
Product SMS 2.0 SMS 2003

Microsoft Office 2000


Yes


No

Microsoft Office XP


Yes


Yes

SMS uses MBSA for detection. Therefore, SMS has the same limitation that is listed earlier in this bulletin related to programs that MBSA does not detect.

For SMS 2.0, the SMS SUS Feature Pack, which includes the Security Update Inventory Tool, can be used by SMS to detect security updates. SMS SUIT uses the MBSA 1.2.1 engine for detection. For more information about the Security Update Inventory Tool, visit the following Microsoft Web site. For more information about the limitations of the Security Update Inventory Tool, see Microsoft Knowledge Base Article 306460. The SMS SUS Feature Pack also includes the Microsoft Office Inventory Tool to detect required updates for Microsoft Office applications.

For SMS 2003, the SMS 2003 Inventory Tool for Microsoft Updates can be used by SMS to detect security updates that are offered by Microsoft Update and that are supported by Windows Server Update Services. For more information about the SMS 2003 Inventory Tool for Microsoft Updates, visit the following Microsoft Web site. SMS 2003 can also use the Microsoft Office Inventory Tool to detect required updates for Microsoft Office applications.

For more information about SMS, visit the SMS Web site.
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Vulnerability Details

Visual Basic for Applications Vulnerability - CVE-2006-3649

A remote code execution vulnerability exists in the way that Visual Basic for Applications (VBA) checks the document properties that a host application passes to it when opening a document. This vulnerability could allow an attacker who successfully exploited the vulnerability to take complete control of the affected system.

Mitigating Factors for Visual Basic for Applications Vulnerability - CVE-2006-3649:


An attacker who successfully exploited this vulnerability could gain the same user rights as the local user. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights.


In Outlook 2002 and Outlook 2003, the vulnerability could not be exploited automatically through e-mail. A user would have to click on an attachment and then acknowledge a warning and accept a prompt to Open before the vulnerability could be exploited.


In a Web-based attack scenario, an attacker could host a Web site that contains a Web page that is used to exploit this vulnerability. In addition, compromised Web sites and Web sites that accept or host user-provided content or advertisements could contain specially crafted content that could exploit this vulnerability. In all cases, however, an attacker would have no way to force users to visit these Web sites. Instead, an attacker would have to persuade users to visit the Web site, typically by getting them to click a link in an e-mail message or instant messenger message that takes users to the attacker's Web site.

Note Office 2000 products do not prompt the user to Open, Save, or Cancel before opening a document.
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Workarounds for Visual Basic for Applications Vulnerability - CVE-2006-3649:

Microsoft has tested the following workarounds. While these workarounds will not correct the underlying vulnerability, they help block known attack vectors. When a workaround reduces functionality, it is identified in the following section.

Do not open or save Microsoft Office files that you receive from un-trusted sources or that you received unexpectedly from trusted sources.

This vulnerability could be exploited when a user opens a file.
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FAQ for Visual Basic for Applications Vulnerability - CVE-2006-3649:

What is the scope of the vulnerability?
A remote code execution vulnerability exists in the way that Visual Basic for Applications (VBA) checks document properties that a host application passes to it when opening a document. This vulnerability could allow an attacker who successfully exploited this vulnerability to take complete control of the affected system.

What causes the vulnerability?
The vulnerability results from the way that VBA checks certain document properties that a host application passes to it when opening a document. As a result, it is possible for the host application to pass unchecked parameters to VBA, causing a buffer overrun condition that could allow arbitrary code to be executed.

What is Visual Basic for Applications (VBA)?
Microsoft VBA is a development technology for developing client desktop packaged applications and integrating them with existing data and systems. Microsoft VBA is based on the Microsoft Visual Basic development system. Microsoft Office products include VBA and make use of VBA to perform certain functions. VBA can also be used to build customized applications based around an existing host application.

What might an attacker use the vulnerability to do?
An attacker who successfully exploited this vulnerability could take complete control of the affected system.

How could an attacker exploit the vulnerability?
In order for an attack to be successful, a user would have to open a specially crafted document sent to them by an attacker. This document could be any type of document that supports VBA, such as a Word document, Excel spreadsheet, PowerPoint presentation. In the case where Microsoft Word is being used as the HTML e-mail editor for Microsoft Outlook, this document could be an e-mail message; however, the user would need to reply to or forward the message in order for the vulnerability to be exploited.

In a Web-based attack scenario, an attacker could host a Web site that contains a Web page that is used to exploit this vulnerability. In addition, compromised Web sites and Web sites that accept or host user-provided content or advertisements could contain specially crafted content that could exploit this vulnerability. In all cases, however, an attacker would have no way to force users to visit these Web sites. Instead, an attacker would have to persuade users to visit the Web site, typically by getting them to click a link in an e-mail message or instant messenger message that takes users to the attacker's Web site.

What systems are primarily at risk from the vulnerability?
Workstations and terminal servers are primarily at risk. Servers could be at more risk if users who have sufficient administrative permissions are given the ability to log on to servers and to run programs. However, best practices strongly discourage allowing this.

What does the update do?
The update removes the vulnerability by modifying the way that Visual Basic for Applications parses the function before it passes the message to the allocated buffer.

When this security bulletin was issued, had this vulnerability been publicly disclosed?
Yes. While the initial report was provided through responsible disclosure, the vulnerability was later disclosed publicly. This security bulletin addresses the publicly disclosed vulnerability as well as additional issues discovered through internal investigations.

When this security bulletin was issued, had Microsoft received any reports that this vulnerability was being exploited?
Yes. When the security bulletin was released, Microsoft had received information that this vulnerability was being exploited.

Acknowledgments

Microsoft thanks the following for working with us to help protect customers:


Ka Chun Leung of Symantec for reporting the Visual Basic for Applications Vulnerability - CVE-2006-3649.


Revisions:


V1.0 (August 8, 2006): Bulletin published.

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