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Actively exploited

CVE-2009-0238 Microsoft Office Remote Code Execution

Microsoft Office Excel contains a remote code execution vulnerability that could allow an attacker to take complete control of an affected system if a user opens a specially crafted Excel file that includes a malformed object.

From the CISA KEV catalogue version 2026.11.06, with Cybergen analysis. Updated 6 Nov 2026.

Our Assessment

Should You Worry?

Patch urgentlyCybergen assessment
  • CISA confirmed exploitation in the wild and added it to the Known Exploited Vulnerabilities catalogue on 14 Apr 2026.
  • Rated High severity (CVSS 8.8, scored by CISA).
  • It has been in the catalogue for 206 days. Systems still unpatched now have almost certainly been scanned for it.
The Vulnerability

What It Is

Microsoft Office Excel 2000 SP3, 2002 SP3, 2003 SP3, and 2007 SP1; Excel Viewer 2003 Gold and SP3; Excel Viewer; Compatibility Pack for Word, Excel, and PowerPoint 2007 File Formats SP1; and Excel in Microsoft Office 2004 and 2008 for Mac allow remote attackers to execute arbitrary code via a crafted Excel document that triggers an access attempt on an invalid object, as exploited in the wild in February 2009 by Trojan.Mdropper.AC.

From Watch to Action

What To Do Now

  1. 1

    Find it

    Search your asset inventory and external attack surface for Microsoft Office. Include cloud images, appliances and anything a supplier runs for you.

    Attack Surface Management
  2. 2

    Fix it

    Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

    Vulnerability Management
  3. 3

    Hunt for compromise

    If an affected system was reachable before you patched, assume it may have been hit. Check logs, new accounts, web shells and outbound connections from the date of exposure.

    Incident Response
  4. 4

    Prove it is fixed

    Rescan or test the system after patching. Upgrades that fail silently and forgotten secondary instances are common.

    Penetration Testing

Vendor Advisories

Regulation

The Compliance Clock

Cyber EssentialsRated high, so if it affects devices in your Cyber Essentials scope, the update must be installed within 14 days of the vendor releasing it.NIS2If exploitation causes a significant incident, essential and important entities owe their CSIRT an early warning within 24 hours and a notification within 72 hours.DORAFinancial entities must classify ICT incidents and send an initial notification for a major incident within strict deadlines, with exploited flaws a common cause.US federal (BOD 22-01)Federal civilian agencies had until 28 Apr 2026 to remediate. A sensible benchmark for everyone else.

General guidance, not legal advice. Your obligations depend on your sector, scope and jurisdiction.

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Evidence

Sources

  1. CISA Known Exploited Vulnerabilities catalogue
  2. NVD: CVE-2009-0238
  3. CVE record: CVE-2009-0238
  4. FIRST EPSS
  5. learn.microsoft.com/en-us/security-updates/securitybulletins/2009/ms09-009
  6. microsoft.com/technet/security/advisory/968272.mspx
  7. vupen.com/english/advisories/2009/1023
  8. exchange.xforce.ibmcloud.com/vulnerabilities/48875
  9. us-cert.gov/cas/techalerts/TA09-104A.html
  10. securityfocus.com/bid/33870
  11. symantec.com/business/security_response/writeup.jsp?docid=2009-022310-4202-99
  12. docs.microsoft.com/en-us/security-updates/securitybulletins/2009/ms09-009