Microsoft Patch Tuesday – October 2021

Patch Tuesday is once again upon us. The October 2021 edition of Patch Tuesday brings us 76 fixes, 3 of which are rated as critical with one actively exploited. We’ve listed the most important changes below.

⚡ TL;DR | Go Straight to the October 2021 Patch Tuesday Audit Report

MysterySnail Zero-day

Dubbed “MysterySnail”, CVE-2021-40449 is an elevation of privilege exploit that has been exploited in the wild according to Kaspersky. This use-after-free vulnerability in the Win32k kernel driver lies in the Win32k NtGdiResetDC function. Alongside the zero-day vulnerability itself, Kaspersky found that: “variants of the malware were detected in widespread espionage campaigns against IT companies, military/defense contractors, and diplomatic entities.“

Two Hyper-V Remote Code Execution Vulnerabilities

Two of the three critically rated fixes are in Hyper-V this month. CVE-2021-38672 and CVE-2021-40461 are both RCE vulnerabilities and while Microsoft has not provided many details of exactly where the vulnerability in Hyper-V resides, the vulnerabilities both score a CVSS 3.1 base score of 8.0. The only detail known details regarding exploitation is that this vulnerability can allow a malicious guest VM to read kernel memory in the host. To exploit the vulnerability the guest VM needs a memory allocation error to occur first, then the bug can be used for a VM escape from guest to host.

Microsoft Word Remote Code Execution Vulnerability

The third critical vulnerability this month is in Microsoft Word. CVE-2021-40486 has a CVSS 3.1 base score of 7.8. Very little is known about the details since Microsoft isn’t releasing much. Microsoft has shared that even the Preview Pane is an attack vector.

Windows Thin PC End of Life

Microsoft’s lightweight Windows 7 version, named Windows Thin PC is going end of life today. Three weeks ago, we released our Windows Thin PC EOL blog post containing a report to help you migrate or decommission any Windows Thin PCs left in your environment.

Run the Patch Tuesday October 2021 Audit Report

To help manage your update progress, we’ve created the Patch Tuesday Audit Report that checks if the assets in your network are on the latest patch updates. The report has been color-coded to see at a glance which machines are up-to-date and which ones still need to be updated. As always, system administrators are urged to update their environment as soon as possible to ensure all endpoints are secured.

Patch Tuesday October 2021 CVE Codes & Titles

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