Microsoft released a security bulletin and software updates to address the invalid object arbitrary code execution vulnerability in Microsoft Office Excel.
Description
Microsoft Office Excel, Office Excel Viewer, Office for Mac, Microsoft Office Compatibility Pack for Word, Excel, and PowerPoint 2007 File Formats contain a vulnerability that could allow an unauthenticated, remote attacker to execute arbitrary code.
The vulnerability is due to an unspecified error when handling invalid objects. An unauthenticated, remote attacker could exploit this vulnerability by convincing a targeted user to open a malicious .xls file. An exploit could allow the attacker to execute arbitrary code with the privileges of the user.
This vulnerability is being exploited actively.
Microsoft confirmed this vulnerability and released software updates.
Warning Indicators
The following Microsoft products are vulnerable:
Microsoft Office Excel 2000 SP3 and prior
Microsoft Office Excel 2002 SP3 and prior
Microsoft Office Excel 2003 SP3 and prior
Microsoft Office Excel 2007 SP1 and prior
Microsoft Office Excel Viewer 2003 and prior
Microsoft Office Excel Viewer 2003 SP3 and prior
Microsoft Office Excel Viewer 2007 and prior
Microsoft Office Compatibility Pack for Word, Excel, and PowerPoint 2007 File Formats SP1 and prior
Microsoft Office for Mac 2004 and prior
Microsoft Office for Mac 2008 and prior
IntelliShield Analysis
Attackers are actively exploiting this vulnerability to conduct limited malicious code attacks that are designed to infect targeted systems with a variant of the Mdropper family of trojans. This family of trojans is detailed in IntelliShield Alert 12562.
It should be noted that the new XML format for Excel, .xlsx, is not affected by this vulnerability. Only the legacy Excel file format, .xls, can be used in an exploit. Sites that do no use the legacy file format can block that file type to prevent exploitation.
The Cisco Applied Intelligence team has created an Applied Mitigation Bulletin to address vulnerabilities that Microsoft disclosed in the April 2009 security bulletin release. This Cisco bulletin, which assists administrators in identifying or mitigating these vulnerabilities using Cisco devices, is available at the following link: Cisco Applied Mitigation Bulletin: Microsoft Security Bulletin Release for April 2009
The update available from Microsoft corrects this vulnerability by ensuring proper processing of Microsoft Excel files.
Vendor Announcements
Microsoft has released a security bulletin at the following link: MS09-009
Microsoft has re-released a security advisory at the following link: 968272
Impact
An unauthenticated, remote attacker could exploit this vulnerability to execute arbitrary code with the privileges of the user. If the user holds Administrator privileges, the attacker could take complete control of the targeted system.
Technical Information
The vulnerability is due to an unspecified error in handling the file format of Excel spreadsheet documents. The processing of a malicious document could corrupt memory in such a way that an attacker could execute arbitrary code. Further technical information is unavailable.
Safeguards
Administrators are advised to apply the available software updates.
Users are advised not to open unsolicited files. Users should verify the authenticity of unexpected files from trusted sources before opening them.
Users may consider applying the Microsoft Office Isolated Conversion Environment (MOICE) to safely open documents from untrusted sources on systems running Microsoft Office 2003 and 2007.
Users are advised to run applications with the least privileges necessary.
Administrators may consider using a host-based intrusion prevention system to help mitigate the impact of an exploit.
Administrators may consider enabling the File Block policy to prevent Excel from opening .xls files until an update can be applied.
Administrators may consider using the Microsoft Baseline Security Analyzer (MBSA) scan tool to identify common security misconfigurations and missing security updates on system endpoints.
Patches/Software
Microsoft customers can obtain updates directly by using the links in the MS09-009 security bulletin. These updates are also distributed by Windows automatic update features and available on the Windows Update website. Microsoft Windows Server Update Services (WSUS), Systems Management Server, and System Center Configuration Manager can assist administrators in deploying software updates.
Signatures
Cisco Systems Cisco Intrusion Prevention System (IPS) 6.0
Version 5, March 6, 2009, 5:42 PM: Microsoft re-released a security advisory to remove the Open XML File Format Converter for Mac products because they are not affected by the invalid object arbitrary code execution vulnerability as original reports indicated.
Version 4, February 26, 2009, 5:03 PM: Microsoft re-released a security advisory with additional products affected by the invalid object arbitrary code execution vulnerability.
Version 3, February 25, 2009, 2:34 PM: Additional details and workaround information is available to address the invalid object arbitrary code execution vulnerability in Microsoft Office Excel.
Version 2, February 24, 2009, 2:31 PM: Microsoft has released a security advisory and workarounds to address the arbitrary code execution vulnerability in Microsoft Office Excel.
Version 1, February 24, 2009, 10:26 AM: Microsoft Office Excel contains a vulnerability that could allow an unauthenticated, remote attacker to execute arbitrary code with the privileges of the user. Updated software is available.
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