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Microsoft Patch Tuesday: Windows Flaw Under Active Attack

The zero-day attacks against Microsoft’s software products continue to pile up with a new warning from Redmond about a zero-day attack hitting a security defect in the Windows Update Medic Service.

The zero-day flaw, documented as CVE-2021-36948, is rated “important” with a CVSS base score of 7.8.

Microsoft described the vulnerability as a local privilege escalation bug, a suggestion that it is part of a larger software exploit chain.

The Windows Update Medic Service is used to repair Windows Update components from damage so that Windows machines can continue to receive software updates. The utility was first introduced in Windows 10 and is an important part of the operating system’s self-healing mechanisms.

This is the 19th documented zero-day attack against Microsoft’s products so far in 2021. Microsoft did not provide any details or indicators of compromise (IOCs) related to this new attack.

[ Related: Microsoft Takes Another Stab at PrintNightmare Security Fix ]

Microsoft's August batch of security patches also provides cover for multiple code execution flaws in a range of Windows OS and platform components.

In all, Microsoft released patches for 44 documented security vulnerabilities in Windows, Microsoft Office, Windows Defender, WIndows Update, Microsoft Dynamics, and Microsoft Azure.

Microsoft said seven of the 44 vulnerabilities are rated “critical” and carry the risk of remote code execution attacks.

The August patches also included cover for a new Windows Print Spooler flaw that Microsoft’s lists as publicly known.   

Separately, Microsoft announced a major default change to the way Windows interacts with the problematic Point and Print driver. Windows will now require admin rights to change the default Point and Print driver installation and update behavior.

This move is meant to be a more comprehensive fix for dangerous security flaws publicly known as PrintNightmare that expose users to remote code execution and privilege escalation attacks.

“Our investigation into several vulnerabilities collectively referred to as “PrintNightmare” has determined that the default behavior of Point and Print does not provide customers with the level of security required to protect against potential attacks,” according to a statement from the Microsoft Security Response Center (MSRC).

[ RelatedDid Microsoft Botch the PrintNightmare Patch? ]

The default change takes effect with the installation of the August batch of security updates for all versions of Windows.   

The PrintNightmare issue has been a public embarrassment for Microsoft as security researchers used social media to highlight major problems with Redmond’s mitigation guidance and the effectiveness of its out-of-band update.

Related: Windows Admins Scrambling to Contain 'PrintNightmare' Flaw 

Related: Microsoft Warns of Under-Attack Windows Kernel Flaw

Related: Microsoft Patch Tuesday: 83 Vulnerabilities, 10 Critical, 1 Actively Exploited

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Ryan Naraine is Editor-at-Large at SecurityWeek and host of the popular Security Conversations podcast series. Ryan is a veteran cybersecurity strategist who has built security engagement programs at major global brands, including Intel Corp., Bishop Fox and GReAT. He is a co-founder of Threatpost and the global SAS conference series. Ryan's past career as a security journalist included bylines at major technology publications including Ziff Davis eWEEK, CBS Interactive's ZDNet, PCMag and PC World. Ryan is a director of the Security Tinkerers non-profit, an advisor to early-stage entrepreneurs, and a regular speaker at security conferences around the world. Follow Ryan on Twitter @ryanaraine.