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  Microsoft Excel memory corruption

From:MICROSOFT <secure_(at)_microsoft.com>
Date:14.08.2007
Subject:Microsoft Security Bulletin MS07-044 - Critical Vulnerability in Microsoft Excel Could Allow Remote Code Execution (940965)

Microsoft Security Bulletin MS07-044 - Critical
Vulnerability in Microsoft Excel Could Allow Remote Code Execution (940965)
Published: August 14, 2007

Version: 1.0
General Information
Executive Summary

This security update resolves a privately reported vulnerability in addition to other security issues identified during the course of the investigation. These vulnerabilities could allow remote code execution if a user opens a specially crafted Excel file. 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.

This is a critical security update for supported editions of Microsoft Office 2000. For supported editions of Microsoft Office XP, Microsoft Office 2003, Microsoft Office 2004 for Mac, this update is rated important. This update is also rated important for the Excel Viewer 2003. For more information, see the subsection, Affected and Non-Affected Software, in this section.

This security update addresses these vulnerabilities by modifying the way that Microsoft Excel handles specially crafted Excel files. For more information about the vulnerabilities, see the Frequently Asked Questions (FAQ) subsection for the specific vulnerability entry under the next section, Vulnerability Information.

Recommendation. Microsoft recommends that customers apply the update immediately.

Known Issues. None
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Affected and Non-Affected Software

The software listed here have been tested to determine which versions or editions are affected. Other versions or editions are either past their support life cycle or are not affected. To determine the support life cycle for your software version or edition, visit Microsoft Support Lifecycle.

Affected Software
Office Suite and Other Affected Software Component Maximum Security Impact Aggregate Severity Rating Bulletins Replaced by This Update

Microsoft Office 2000 Service Pack 3


Microsoft Office 2000 Service Pack 3


Remote Code Execution


Critical


MS07-036

Microsoft Office XP Service Pack 3


Microsoft Office XP Service Pack 3


Remote Code Execution


Important


MS07-036

Microsoft Office 2003 Service Pack 2


Microsoft Office 2003 Service Pack 2

Microsoft Excel Viewer 2003


Remote Code Execution


Important


MS07-036

Microsoft Office 2004 for Mac


Microsoft Office 2004 for Mac


Remote Code Execution


Important


MS07-036
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Frequently Asked Questions (FAQ) Related to This Security Update

Why does this update address several reported security vulnerabilities?
This update addresses several vulnerabilities because the modifications for these issues are located in related files. Instead of having to install several updates that are almost the same, customers need to install this update only.

I do not have any of the Affected Software installed, but I do have other Microsoft Office applications installed. Why am I being offered the security update?
The vulnerabilities described in this security update exist within Microsoft Office but could not be exploited using other Microsoft applications that are not vulnerable. Other Microsoft Office applications may use some of the same files as the applications listed in the Affected Software that the security update affects. We recommend installing the update to prevent the security update from being offered again.

I am using an older release of the software discussed in this security bulletin. What should I do?
The affected software listed in this bulletin have been tested to determine which releases are affected. Other releases are past their support life cycle. To determine the support life cycle for your software release, visit Microsoft Support Lifecycle.

It should be a priority for customers who have older releases of the software to migrate to supported releases to prevent potential exposure to vulnerabilities. For more information about the Windows Product Lifecycle, visit the following Microsoft Support Lifecycle. For more information about the extended security update support period for these software releases, visit the Microsoft Product Support Services Web site.

Customers who require custom support for older software must contact their Microsoft account team representative, their Technical Account Manager, or the appropriate Microsoft partner representative for custom support options. Customers without an Alliance, Premier, or Authorized Contract can contact their local Microsoft sales office. For contact information, visit the Microsoft Worldwide Information Web site, select the country, and then click Go to see a list of telephone numbers. When you call, ask to speak with the local Premier Support sales manager. For more information, see the Windows Operating System Product Support Lifecycle FAQ.
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Vulnerability Information

Severity Ratings and Vulnerability Identifiers
Vulnerability Severity Rating and Maximum Security Impact by Affected Software
Affected Software Workspace Memory Corruption Vulnerability – CVE-2007-3890 Aggregate Severity Rating

Microsoft Excel 2000 Service Pack 3


Critical
Remote Code Execution


Critical

Microsoft Excel 2002 Service Pack 3


Important
Remote Code Execution


Important

Microsoft Excel 2003 Service Pack 2


Important
Remote Code Execution


Important

Microsoft Excel 2003 Viewer


Important
Remote Code Execution


Important

Microsoft Office 2004 for Mac


Important
Remote Code Execution


Important
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Workspace Memory Corruption Vulnerability – CVE-2007-3890

A remote code execution vulnerability exists in the way Excel handles malformed Excel files. An attacker could exploit the vulnerability by sending a malformed file which could be included as an e-mail attachment, or hosted on a malicious or compromised Web site.

To view this vulnerability as a standard entry in the Common Vulnerabilities and Exposures list, see CVE-2007-3890.

Mitigating Factors for Workspace Memory Corruption Vulnerability – CVE-2007-3890

Mitigation refers to a setting, common configuration, or general best-practice, existing in a default state, that could reduce the severity of exploitation of a vulnerability. The following mitigating factors may be helpful in your situation:


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.


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.


The vulnerability cannot be exploited automatically through e-mail. For an attack to be successful a user must open an attachment that is sent in an e-mail message.


Users who have installed and are using the Office Document Open Confirmation Tool for Office 2000 will be prompted with Open, Save, or Cancel before opening a document. The features of the Office Document Open Confirmation Tool are incorporated in Office XP and later editions of Office.
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Workarounds for Workspace Memory Corruption Vulnerability – CVE-2007-3890

Workaround refers to a setting or configuration change that does not correct the underlying vulnerability but would help block known attack vectors before you apply the update. Microsoft has tested the following workarounds and states in the discussion whether a workaround reduces functionality:


Use Microsoft Office File Block policy to block the opening of Office 2003 and earlier documents from unknown or un-trusted sources and locations.

The following registry scripts can be used to set the File Block policy.

Note Modifying the Registry incorrectly can cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that problems resulting from incorrect modification of the Registry can be solved. Modify the Registry at your own risk.

For Office 2003

Windows Registry Editor Version 5.00

[HKEY_CURRENT_USER\Software\Microsoft\Office\11.
0\Excel\Security\FileOpenBlock]

"BinaryFiles"=dword:00000001.

Note In order to use 'FileOpenBlock' with Office 2003, all of the latest Office 2003 security updates as of May 2007 must be applied.

Impact of Workaround: Users who have configured the File Block policy and have not configured a special “exempt directory” as discussed in Microsoft Knowledge Base Article 92248 will be unable to open Office 2003 files or earlier versions in Office 2003 or 2007 Microsoft Office System.


Do not open or save Microsoft Office files that you receive from untrusted sources or that you receive unexpectedly from trusted sources. This vulnerability could be exploited when a user opens a specially crafted file.
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FAQ for Workspace Memory Corruption Vulnerability – CVE-2007-3890

What is the scope of the vulnerability?
This is a remote code execution vulnerability. An attacker who successfully exploited this vulnerability could take complete control of an affected system remotely. An attacker could then install programs or view, change, or delete data; or create new accounts with full user rights.

What causes the vulnerability?
Excel does not perform sufficient validation when denoting the index value for a Workspace.

What might an attacker use the vulnerability to do?
An attacker who successfully exploited this vulnerability could run arbitrary code as the logged on user. If a user is logged on with administrative user rights, an attacker could take complete control of the 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.

How could an attacker exploit the vulnerability?
This vulnerability requires that a user open a specially crafted Excel file with an affected version of Microsoft Excel.

In an e-mail attack scenario, an attacker could exploit the vulnerability by sending a specially-crafted Excel file to the user and by convincing the user to open the file.

In a Web-based attack scenario, an attacker would have to host a Web site that contains an Excel file that is used to attempt to exploit this vulnerability. In addition, compromised Web sites and Web sites that accept or host user-provided content could contain specially crafted content that could exploit this vulnerability. An attacker would have no way to force users to visit a specially crafted Web site. Instead, an attacker would have to persuade them to visit the Web site, typically by getting them to click a link that takes them to the attacker's site.

What systems are primarily at risk from the vulnerability?
Systems where Microsoft Excel is used are primarily at risk. Servers could be at more risk if administrators allow users 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 Microsoft Excel validates the index value attributes associated with a Workspace.

When this security bulletin was issued, had this vulnerability been publicly disclosed?
No. Microsoft received information about this vulnerability through responsible disclosure. Microsoft had not received any information to indicate that this vulnerability had been publicly disclosed when this security bulletin was originally issued. This security bulletin addresses the privately 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?
No. Microsoft had not received any information to indicate that this vulnerability had been publicly used to attack customers and had not seen any examples of proof of concept code published when this security bulletin was originally issued.

Other Information
Acknowledgments

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


Dyon Balding of Secunia for reporting the Workspace Memory Corruption Vulnerability (CVE-2007-3890)
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Support


Customers in the U.S. and Canada can receive technical support from Microsoft Product Support Services at 1-866-PCSAFETY. There is no charge for support calls that are associated with security updates.


International customers can receive support from their local Microsoft subsidiaries. There is no charge for support that is associated with security updates. For more information about how to contact Microsoft for support issues, visit the International Support Web site.
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Disclaimer

The information provided in the Microsoft Knowledge Base is provided "as is" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply.
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Revisions


V1.0 (August 14, 2007): Bulletin published.

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