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Related information

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  iDefense Security Advisory 12.10.08: Microsoft Excel Malformed Object Memoy Corruption Vulnerability

  CORE-2008-0228: Microsoft Word Malformed FIB Arbitrary Free Vulnerability

  ZDI-08-086: Microsoft Office Word Document Table Property Stack Overflow Vulnerability

  ZDI-08-085: Microsoft Office RTF Drawing Object Heap Overflow Vulnerability

From:MICROSOFT <secure_(at)_microsoft.com>
Date:10.12.2008
Subject:Microsoft Security Bulletin MS08-074 - Critical Vulnerabilities in Microsoft Office Excel Could Allow Remote Code Execution (959070)

Microsoft Security Bulletin MS08-074 - Critical
Vulnerabilities in Microsoft Office Excel Could Allow Remote Code Execution (959070)
Published: December 9, 2008

Version: 1.0
General Information
Executive Summary

This security update resolves three privately reported vulnerabilities in Microsoft Office Excel that could allow remote code execution if a user opens a specially crafted Excel file. An attacker who successfully exploited these vulnerabilities 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.

This security update is rated Critical for all supported editions of Microsoft Office Excel 2000. For all supported editions of Microsoft Office Excel 2002, Microsoft Office Excel 2003, Microsoft Office Excel Viewer 2003, Microsoft Office Excel 2007, Microsoft Office Compatibility Pack, Microsoft Office Excel Viewer, Microsoft Office 2004 for Mac, Microsoft Office 2008 for Mac, and Open XML File Format Converter for Mac, this security update is rated Important. 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 Office Excel opens Excel files. For more information about the vulnerability, 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. Microsoft Knowledge Base Article 959070 documents the currently known issues that customers may experience when installing this security update. The article also documents recommended solutions for these issues.
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Affected and Non-Affected Software

The following software 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 Software Component Maximum Security Impact Aggregate Severity Rating Bulletins Replaced by this Update
Microsoft Office Suites and Components

Microsoft Office 2000 Service Pack 3


Microsoft Office Excel 2000 Service Pack 3
(KB958435)


Remote Code Execution


Critical


MS08-057

Microsoft Office XP Service Pack 3


Microsoft Office Excel 2002 Service Pack 3
(KB958372)


Remote Code Execution


Important


MS08-057

Microsoft Office 2003 Service Pack 3


Microsoft Office Excel 2003 Service Pack 3
(KB958436)


Remote Code Execution


Important


MS08-057

2007 Microsoft Office System


Microsoft Office Excel 2007
(KB958437)


Remote Code Execution


Important


MS08-057

2007 Microsoft Office System Service Pack 1


Microsoft Office Excel 2007 Service Pack 1
(KB958437)


Remote Code Execution


Important


MS08-057
Other Office Software

Microsoft Office Excel Viewer 2003
(KB958434)


Not applicable


Remote Code Execution


Important


MS08-057

Microsoft Office Excel Viewer 2003 Service Pack 3
(KB958434)


Not applicable


Remote Code Execution


Important


MS08-057

Microsoft Office Excel Viewer
(KB958442)


Not applicable


Remote Code Execution


Important


MS08-057

Microsoft Office Compatibility Pack for Word, Excel, and PowerPoint 2007 File Formats
(KB958439)


Not applicable


Remote Code Execution


Important


MS08-057

Microsoft Office Compatibility Pack for Word, Excel, and PowerPoint 2007 File Formats Service Pack 1
(KB958439)


Not applicable


Remote Code Execution


Important


MS08-057
Microsoft Office for Mac

Microsoft Office 2004 for Mac
(KB960402)


Not applicable


Remote Code Execution


Important


MS08-057

Microsoft Office 2008 for Mac
(KB960401)


Not applicable


Remote Code Execution


Important


MS08-057

Open XML File Format Converter for Mac
(KB960403)


Not applicable


Remote Code Execution


Important


MS08-057

Non-Affected Software
Office and Other Software

Microsoft Works 8.5

Microsoft Works 9.0

Microsoft Works Suite 2005

Microsoft Works Suite 2006

Microsoft Office SharePoint Server 2003 Service Pack 3

Microsoft Office SharePoint Server 2007 and Microsoft Office SharePoint Server 2007 Service Pack 1 (32-bit editions)

Microsoft Office SharePoint Server 2007 and Microsoft Office SharePoint Server 2007 Service Pack 1 (64-bit editions)
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Frequently Asked Questions (FAQ) Related to This Security Update

Where are the file information details?
The file information details can be found in Microsoft Knowledge Base Article 959070.

MS08-072 also describes vulnerabilities in Microsoft Office 2004 for Mac, Microsoft Office 2008 for Mac, and Open XML File Format Converter for Mac. How does MS08-072relate to this bulletin (MS08-074)?
This security update for Microsoft Office 2004 for Mac (960402), Microsoft Office 2008 for Mac (960401), and Open XML File Format Converter for Mac (960403) also addresses the vulnerabilities described in MS08-072. Users with Microsoft Office 2004 for Mac, Microsoft Office 2008 for Mac, or Open XML File Format Converter for Mac installed will have to install this security update but will only need to install it once.

What is the Microsoft Office Excel Viewer?
The Microsoft Office Excel Viewer is a replacement for all previous Excel Viewer versions, including Excel Viewer 97 and Excel Viewer 2003. With Excel Viewer, you can open, view, and print Excel workbooks, even if you don't have Excel installed. You can also copy data from Excel Viewer to another program. However, you cannot edit data, save a workbook, or create a new workbook.

What components of the Microsoft Office Compatibility Pack for Word, Excel, and PowerPoint 2007 File Formats are updated by this bulletin?
The update included with this security bulletin applies only to the specific component within the Microsoft Office Compatibility Pack for Word, Excel, and PowerPoint 2007 File Formats that is affected. For example, in an Excel bulletin, only the Excel compatibility pack component files are included in the update packages and not Word or PowerPoint compatibility pack component files. Word compatibility pack component files are updated in a Word bulletin and PowerPoint compatibility pack component files are updated in a PowerPoint bulletin.

Why does this update address several reported security vulnerabilities?
This update contains support for several vulnerabilities because the modifications that are required to address 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.

The Office component discussed in this article is part of the Office Suite that I have installed on my system; however, I did not choose to install this specific component. Will I be offered this update?
Yes, if the version of the Office Suite installed on your system shipped with the component discussed in this bulletin, the system will be offered updates for it whether the component is installed or not. The detection logic used to scan for affected systems is designed to check for updates for all components that shipped with the particular Office Suite and offer the updates to a system. Users who choose not to apply an update for a component that is not installed, but is included in the version of the Office Suite, will not increase the security risk of that system. However, users who do choose to install the update will not have a negative impact on the security or performance of a system. For more information on this issue, please see Microsoft Knowledge Base Article 830335.

Does the offer to update a non-vulnerable version of Microsoft Office constitute an issue in the Microsoft update mechanism?
No, the update mechanism is functioning correctly in that it detects a lower version of the files on the system than in the update package and thus, offers the update.

I use Microsoft Office 2007 RTM. Are any additional security features included in this update?
Yes, as part of the servicing model for Microsoft Office 2007, when users of Microsoft Office 2007 RTM install this update, their systems will be upgraded to functionality that was initially released with Microsoft Office 2007 Service Pack 1. All updates released after December 8, 2007 for Microsoft Office 2007 will include these security features, which were introduced in Microsoft Office 2007 Service Pack 1. We have thoroughly tested this update, but as with all updates, we recommend that users perform testing appropriate to the environment and configuration of their systems.

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 Microsoft Support Lifecycle. For more information about the extended security update support period for these software versions or editions, visit Microsoft Product Support Services.

Customers who require custom support for older releases 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 Microsoft Worldwide Information, 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 File Format Parsing Vulnerability - CVE-2008-4265 File Format Parsing Vulnerability - CVE-2008-4264 Excel Global Array Memory Corruption Vulnerability - CVE-2008-4266 Aggregate Severity Rating

Microsoft Office Excel 2000 Service Pack 3


Critical

Remote Code Execution


Critical

Remote Code Execution


Critical

Remote Code Execution


Critical

Microsoft Office Excel 2002 Service Pack 3


None


Important

Remote Code Execution


Important

Remote Code Execution


Important

Microsoft Office Excel 2003 Service Pack 3


None


Important

Remote Code Execution


Important

Remote Code Execution


Important

Microsoft Office Excel 2007


None


Important

Remote Code Execution


None


Important

Microsoft Office Excel 2007 Service Pack 1


None


Important

Remote Code Execution


None


Important

Microsoft Office Excel Viewer 2003


None


Important

Remote Code Execution


Important

Remote Code Execution


Important

Microsoft Office Excel Viewer 2003 Service Pack 3


None


Important

Remote Code Execution


Important

Remote Code Execution


Important

Microsoft Office Excel Viewer


None


Important

Remote Code Execution


None


Important

Microsoft Office Compatibility Pack for Word, Excel, and PowerPoint 2007 File Formats


None


Important

Remote Code Execution


None


Important

Microsoft Office Compatibility Pack for Word, Excel, and PowerPoint 2007 File Formats Service Pack 1


None


Important

Remote Code Execution


None


Important

Microsoft Office 2004 for Mac


None


Important

Remote Code Execution


Important

Remote Code Execution


Important

Microsoft Office 2008 for Mac


None


Important

Remote Code Execution


Important

Remote Code Execution


Important

Open XML File Format Converter for Mac


None


Important

Remote Code Execution


Important

Remote Code Execution


Important
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File Format Parsing Vulnerability - CVE-2008-4265

A remote code execution vulnerability exists in Microsoft Office Excel as a result of memory corruption when loading Excel records. The vulnerability could allow remote code execution if a user opens a specially crafted Excel file that includes a malformed object. 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.

To view this vulnerability as a standard entry in the Common Vulnerabilities and Exposures list, see CVE-2008-4265.

Mitigating Factors for File Format Parsing Vulnerability - CVE-2008-4265

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:


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 Office 2003.
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Workarounds for File Format Parsing Vulnerability - CVE-2008-4265

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:


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 File Format Parsing Vulnerability - CVE-2008-4265

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?
A vulnerability exists in Microsoft Office Excel that allows an attacker to execute code when a user of an affected version of Excel opens a specially crafted attacker-supplied Excel spreadsheet. The specific vulnerability exists in the way Microsoft Office Excel parses the Excel spreadsheet file format.

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 spreadsheet with an affected version of Microsoft Office 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 Office 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 convince them to visit the Web site, typically by getting them to click a link that takes them to the attacker's site, and then convincing them to open the specially crafted Excel file.

What systems are primarily at risk from the vulnerability?
Systems where the Microsoft Office Excel is used, including workstations and terminal servers, 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?
This update removes the vulnerability by changing the way Microsoft Office Excel handles opening specially crafted Excel files

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 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.
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File Format Parsing Vulnerability - CVE-2008-4264

A remote code execution vulnerability exists in Microsoft Office Excel as a result of pointer corruption when loading Excel formulas. The vulnerability could allow remote code execution if a user opens a specially crafted Excel file that includes a malformed formula. 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.

To view this vulnerability as a standard entry in the Common Vulnerabilities and Exposures list, see CVE-2008-4264.

Mitigating Factors for File Format Parsing Vulnerability - CVE-2008-4264

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:


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 Office 2003.
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Workarounds for File Format Parsing Vulnerability - CVE-2008-4264

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 the Microsoft Office Isolated Conversion Environment (MOICE) when opening files from unknown or un-trusted sources

The Microsoft Office Isolated Conversion Environment (MOICE) will protect Office 2003 installations by more securely opening Word, Excel, and PowerPoint binary format files.

To install MOICE, you must have Office 2003 or 2007 Office system installed.

To install MOICE, you must have the Compatibility Pack for Word, Excel, and PowerPoint 2007 File Formats. The compatibility pack is available as a free download from the Microsoft Download Center:

Download the FileFormatConverters.exe package now

MOICE requires all updates that are recommended for all Office programs. Visit Microsoft Update to install all recommended updates:

http://update.microsoft.com/microsoftupdate/v6/default.aspx?ln=en-us

To enable MOICE, change the registered handler for the .xls, .xlt, and .xla file formats. The following table describes the command to enable or to disable MOICE for the .xls, .xlt, and .xla file formats:
Command to use to enable MOICE to be the registered handler Command to use to disable MOICE as the registered handler

ASSOC .XLS=oice.excel.sheet


ASSOC .xls=Excel.Sheet.8

ASSOC .XLT=oice.excel.template


ASSOC .xlt=Excel.Template

ASSOC .XLA=oice.excel.addin


ASSOC .xla=Excel.Addin

Note On Windows Vista and Windows Server 2008 the commands above will need to be run from an elevated command prompt.

For more information on MOICE, see Microsoft Knowledge Base Article 935865.

Impact of Workaround: Office 2003 and earlier formatted documents that are converted to the 2007 Microsoft Office System Open XML format by MOICE will not retain macro functionality. Additionally, documents with passwords or that are protected with Digital Rights Management cannot be converted.


Use Microsoft Office File Block policy to block the opening of Office 2003 and earlier documents from unknown or untrusted 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 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 922848 will be unable to open Office 2003 files or earlier versions in Office 2003 or 2007 Microsoft Office System.

For 2007 Office system

Windows Registry Editor Version 5.00

[HKEY_CURRENT_USER\Software\Microsoft\Office\12.
0\Excel\Security\FileOpenBlock]

"BinaryFiles"=dword:00000001

Note In order to use 'FileOpenBlock' with the 2007 Microsoft Office system, all of the latest security updates for the 2007 Microsoft Office system 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 922848 will be unable to open Office 2003 files or earlier versions in Office 2003 or 2007 Microsoft Office System.

How to Undo the Workaround:

For Office 2003

Windows Registry Editor Version 5.00

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

"BinaryFiles"=dword:00000000

For 2007 Office system

Windows Registry Editor Version 5.00

[HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\12.
0\Excel\Security\FileOpenBlock]

"BinaryFiles"=dword:00000000
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FAQ for File Format Parsing Vulnerability - CVE-2008-4264

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?
A vulnerability exists in Microsoft Office Excel that could allow an attacker to execute code when a user of an affected version of Excel opens a specially crafted attacker-supplied Excel spreadsheet. The specific vulnerability exists in the way Microsoft Office Excel parses the Excel spreadsheet file format.

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 spreadsheet with an affected version of Microsoft Office Excel.

In an e-mail attack scenario, an attacker could exploit the vulnerability by sending a specially crafter 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 Office 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 convince them to visit the Web site, typically by getting them to click a link that takes them to the attacker's site, and then convincing them to open the specially crafted Excel file.

What systems are primarily at risk from the vulnerability?
Systems where the Microsoft Office Excel is used, including workstations and terminal servers, 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?
This update removes the vulnerability by changing the way Microsoft Office Excel handles opening specially crafted Excel files.

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 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.
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Excel Global Array Memory Corruption Vulnerability - CVE-2008-4266

A remote code execution vulnerability exists in Microsoft Office Excel as a result of stack corruption when loading Excel records. The vulnerability could allow remote code execution if a user opens a specially crafted Excel file that includes a malformed object. 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.

To view this vulnerability as a standard entry in the Common Vulnerabilities and Exposures list, see CVE-2008-4266.

Mitigating Factors for Excel Global Array Memory Corruption Vulnerability - CVE-2008-4266

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:


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 Office 2003.
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Workarounds for Excel Global Array Memory Corruption Vulnerability - CVE-2008-4266

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:


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 Excel Global Array Memory Corruption Vulnerability - CVE-2008-4266

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?
A vulnerability exists in Microsoft Office Excel that allows an attacker to execute code when a user of an affected version of Excel opens a specially crafted attacker-supplied Excel spreadsheet. The specific vulnerability exists in the way Microsoft Office Excel parses the Excel spreadsheet file format.

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 spreadsheet with an affected version of Microsoft Office 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 Office 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 convince them to visit the Web site, typically by getting them to click a link that takes them to the attacker's site, and then convincing them to open the specially crafted Excel file.

What systems are primarily at risk from the vulnerability?
Systems where the Microsoft Office Excel is used, including workstations and terminal servers, 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?
This update removes the vulnerability by changing the way Microsoft Office Excel handles opening specially crafted Excel files.

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 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:


Joshua J. Drake of VeriSign iDefense Labs for reporting the File Format Parsing Vulnerability (CVE-2008-4265)


Claes M Nyberg of signedness.org for reporting the File Format Parsing Vulnerability (CVE-2008-4264)


Dyon Balding of Secunia for reporting the Excel Global Array Memory Corruption Vulnerability (CVE-2008-4266)
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Microsoft Active Protections Program (MAPP)

To improve security protections for customers, Microsoft provides vulnerability information to major security software providers in advance of each monthly security update release. Security software providers can then use this vulnerability information to provide updated protections to customers via their security software or devices, such as antivirus, network-based intrusion detection systems, or host-based intrusion prevention systems. To determine whether active protections are available from security software providers, please visit the active protections Web sites provided by program partners, listed in Microsoft Active Protections Program (MAPP) Partners.
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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.

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.

Revisions


V1.0 (December 9, 2008): Bulletin published.

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