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Microsoft December 2021 Patch Tuesday Brings Fix for Active Emotet Exploit Zero-Day

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icrosoft rolled out its December 2021 Patch Tuesday updates yesterday. As usual, dozens of fixes (67 in total) were included in the cumulative updates, including one for a zero-day vulnerability that is already being exploited in the wild.

This flaw is concerning because it sends the Emotet Trickbot to unsuspecting users through a fake application. Microsoft has been tracking the vulnerability as CVE-2021-43890 and given it an “important” rating.

Microsoft describes the problem as a spoofing vulnerability found in the Windows AppX Installer. This means it affects Windows 10 apps. Windows AppX Installer is available from the App Store an allows users to side-load Windows applications.

Attackers can exploit the vulnerability by creating a package file and modifying it to look like a real application. Instead, it is loaded with the Emotet trickbot malware.

Yes, that’s the same Emotet that Microsoft declared war on and removed earlier this year. However, it has since made a comeback. Emotet is a relatively old and solvable trojan that has been around since 2014. However, threat actors have evolved the botnet to become the most dangerous in circulation.

It is used by a threat group known as Mummy Spider (TA542) to deploy other malware types such as Trickbot.


Microsoft says the December 2021 Patch Tuesday fix should shore app Windows AppX Installer and fake packages will no longer appear legitimate. However, the company points out the patch does not stop the threat actors from sending the files.

The Patch Tuesday Cumulative updates for December 2021 are rolling out now. Amongst the 67 fixes are patches covering vulnerabilities in Microsoft Edge, Microsoft Office, SharePoint, Windows, Azure Bot Framework SDK, Visual Studio, ASP.NET Core, Microsoft Defender for IoT, and more.

Tip of the day: Whether it’s for a presentation, song, or YouTube video, at some point in your life you’ll need to record audio from your computer. Windows 11 has multiple options to record sound due to its litany of apps. In our tutorial, we show you how to record audio using the built-in Windows 10 Voice Recorder and the freeware audio editor Audacity.

Source Winbuzzer

Juliana Luwoye

The author Juliana Luwoye

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