An ancient Microsoft Excel security flaw could let hackers hijack your entire system, so patch now

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CISA is warning about ongoing exploitation of a 2008 bug

Someone using Excel on a Laptop.
(Image credit: Microsoft)
  • CISA adds 18‑year‑old Excel flaw (CVE‑2009‑0238) to KEV catalog
  • Vulnerability enables RCE via malicious Excel files, patched long ago
  • Outdated systems still at risk; agencies ordered to patch by April 28

Incredible as it may sound, there are still systems out there vulnerable to 18-year-old Microsoft Excel vulnerabilities, and unsurprisingly, cybercriminals are taking advantage of that fact.

The US Cybersecurity and Infrastructure Security Agency (CISA) recently updated its Known Exploited Vulnerabilities (KEV) catalog - a list of flaws confirmed to be exploited in the wild, to add CVE-2009-0238, a bug in Microsoft Excel first discovered in 2009.

According to the National Vulnerability Database (NVD), the bug allows threat actors to execute arbitrary code (RCE) via a crafted Excel document “that triggers an access attempt on an invalid object”.

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A week to patch

This vulnerability, given a severity score of 8.8/10 (high), was first observed delivering the Trojan.Mdropper.AC malware.

It affects 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. It was patched literally ages ago.

Still, it seems that there are systems out there still using this severely outdated, and thus vulnerable, software. CISA added the bug to KEV on April 14 2026, and gave FCEB agencies a week’s time to patch up (April 28).

Other than that, we don’t know much about who is exploiting the bug and to what end. CISA could not say if the flaw was being used in ransomware infections, or not. We can assume that the attacks include a phishing email with a weaponized Excel document.

Furthermore, if we assume that versions not on the list are safe, that would mean anyone running these is not at risk:

Excel 2007 (SP2 and later)
Excel 2010
Excel 2013
Excel 2016
Excel 2019
Excel 2021
Excel for Microsoft 365 (all versions)
Excel for Mac (versions newer than 2008).

Via The Register

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Sead Fadilpašić

Sead is a seasoned freelance journalist based in Sarajevo, Bosnia and Herzegovina. He writes about IT (cloud, IoT, 5G, VPN) and cybersecurity (ransomware, data breaches, laws and regulations). In his career, spanning more than a decade, he’s written for numerous media outlets, including Al Jazeera Balkans. He’s also held several modules on content writing for Represent Communications.

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