Microsoft Excel Object Record Corruption Remote Code Execution Vulnerability (CVE-2009-0557, MS09-021)
Executive & SecOps Summary
SECOPS ASSESSMENTMicrosoft Office 2000 SP3, XP SP3, 2003 SP3, 2007 SP1/SP2, Office for Mac 2004/2008, Excel Viewer, and Compatibility Pack
Remote attackers can execute arbitrary code with the privileges of the active user by tricking them into opening a specially crafted Excel file
Immediately apply the official Microsoft MS09-021 security update and restrict the execution of untrusted spreadsheet files
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
This vulnerability is resolved by applying the MS09-021 security update. For legacy systems, you can use the following PowerShell commands to check and install the required security updates:
# Install and force Windows Update for MS09-021 related KBs
Install-Module PSWindowsUpdate -Force -Verbose
Get-WindowsUpdate -KBArticleID KB969682, KB969679, KB969680 -Install -AcceptAll -AutoReboot2. Temporary Workaround & Hardening Configuration
If immediate patching is not feasible, you can block legacy binary Excel files from being opened by configuring the File Block settings via the registry:
# Block opening of legacy Excel Binary Files (.xls) via Registry (Excel 2007)
New-ItemProperty -Path 'HKCU:\Software\Policies\Microsoft\Office\12.0\Excel\Security\FileOpenBlock' -Name 'BinaryFiles' -Value 1 -PropertyType DWord -Force3. Log Audit & IoC Verification Commands
You can verify the installed version of the Excel executable to determine if the system remains vulnerable to CVE-2009-0557:
# Check Excel executable version to verify patch status
$ExcelPath = (Get-ItemProperty -Path 'HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\App Paths\excel.exe' -ErrorAction SilentlyContinue).'(default)'
if ($ExcelPath) {
$FileVersion = (Get-Item $ExcelPath).VersionInfo.FileVersion
Write-Host 'Current Excel Version:' $FileVersion
# Example: Excel 2003 (11.0) must be version 11.0.8307.0 or higher after patching
if ([Version]$FileVersion -lt [Version]'11.0.8307.0') {
Write-Warning 'Vulnerable Excel version detected! Apply MS09-021 immediately.'
} else {
Write-Host 'Excel is patched and secure.' -ForegroundColor Green
}
} else {
Write-Host 'Excel is not installed on this machine.'
}Block Kernel Privilege Escalation & Ransomware Payloads Before You Can Reboot
Protect unpatched Windows, Linux, and macOS workloads against in-memory exploitation and lateral movement with autonomous EDR.
Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability exists in Microsoft Excel's parsing engine when processing legacy binary file formats (.xls) containing malformed record objects. Due to insufficient validation and boundary checks of specific object records within the Excel file structure, a memory corruption condition (CWE-94) can be triggered when a corrupted record is loaded into memory. This allows an attacker to disrupt the application's execution flow and redirect it to arbitrary code.
2. Exploitation Mechanics & Attack Scenario
An attacker crafts a malicious Excel spreadsheet containing a corrupted object record designed to trigger memory corruption upon parsing. The file is typically distributed via spear-phishing emails, malicious web downloads, or social engineering tactics. When a victim opens the file using an unpatched version of Excel or Excel Viewer, the application attempts to parse the malformed record, leading to memory corruption and executing the embedded shellcode under the context of the current user.
3. Infrastructure & Business Impact
As a vulnerability listed in the CISA KEV catalog, this flaw has been actively exploited in the wild. Successful exploitation grants the attacker the same system privileges as the local user. If the victim is logged in with administrative rights, the attacker can gain complete control of the affected system, install unauthorized programs, perform lateral movement within the corporate network, and exfiltrate sensitive business data.
Official Vendor Advisories & References
Excel in Microsoft Office 2000 SP3, Office XP SP3, Office 2003 SP3, and Office 2004 and 2008 for Mac; Excel in 2007 Microsoft Office System SP1 and SP2; Open XML File Format Converter for Mac; Microsoft Office Excel Viewer 2003 SP3; Microsoft Office Excel Viewer; and Microsoft Office Compatibility Pack for Word, Excel, and PowerPoint 2007 File Formats SP1 and SP2 allow remote attackers to execute arbitrary code via a crafted Excel file with a malformed record object, aka "Object Record Corruption Vulnerability."
Frequently Asked SecOps Questions (CVE-2009-0557)
FAQQ1. How critical is CVE-2009-0557 and is it actively exploited in the wild?
CVE-2009-0557 is rated CVSS 7.8 (HIGH) with a 30-day EPSS exploitation probability of 52.8%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2009-0557?
Primary impacted vendors include microsoft, apple across excel, office, office for mac, excel viewer, compatibility pack. Scope summary: Microsoft Excel 2000 SP3, XP SP3, 2003 SP3, 2007 SP1/SP2, Office for Mac 2004/2008, Excel Viewer 2003 SP3, and Microsoft Office Compatibility Pack SP1/SP2
Q3. What temporary mitigations or workarounds exist for CVE-2009-0557 before patching?
[Mitigation] Immediately apply the official Microsoft MS09-021 security update and restrict the execution of untrusted spreadsheet files Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
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