Microsoft Patch Tuesday, March 2021 Edition

On the off chance you were looking for more security to-dos from Microsoft today…the company released software updates to plug more than 82 security flaws in Windows and other supported software. Ten of these earned Microsoft’s “critical” rating, meaning they can be exploited by malware or miscreants with little or no help from users.

Top of the heap this month (apart from the ongoing, global Exchange Server mass-compromise) is a patch for an Internet Explorer bug that is seeing active exploitation. The IE weakness — CVE-2021-26411 — affects both IE11 and newer EdgeHTML-based versions, and it allows attackers to run a file of their choice by getting you to view a hacked or malicious website in IE.

The IE flaw is tied to a vulnerability that was publicly disclosed in early February by researchers at ENKI who claim it was one of those used in a recent campaign by nation-state actors to target security researchers. In the ENKI blog post, the researchers said they will publish proof-of-concept (PoC) details after the bug has been patched.

“As we’ve seen in the past, once PoC details become publicly available, attackers quickly incorporate those PoCs into their attack toolkits,” said Satnam Narang, staff research engineer at Tenable. “We strongly encourage all organizations that rely on Internet Explorer and Microsoft Edge (EdgeHTML-Based) to apply these patches as soon as possible.”

This is probably a good place to quote Ghacks.net’s Martin Brinkman: This is the last patch hurrah for the legacy Microsoft Edge web browser, which is being retired by Microsoft.

For the second month in a row, Microsoft has patched scary flaws in the DNS servers on Windows Server 2008 through 2019 versions that could be used to remotely install software of the attacker’s choice. All five of the DNS bugs quashed in today’s patch batch earned a CVSS Score (danger metric) of 9.8 — almost as bad as it gets.

“There is the outside chance this could be wormable between DNS servers,” warned Trend Micro’s Dustin Childs.

As mentioned above, hundreds of thousands of organizations are in the midst dealing with a security nightmare after having their Exchange Server and Outlook Web Access (OWA) hacked and retrofitted with a backdoor. If an organization you know has been affected by this attack, please have them check with the new victim notification website mentioned in today’s story.

Susan Bradley over at Askwoody.com says “nothing in the March security updates (besides the Exchange ones released last week) is causing me to want to urge you to go running to your machines and patch at this time.” I’d concur, unless of course you cruise the web with older Microsoft browsers.

It’s a good idea for Windows users to get in the habit of updating at least once a month, but for regular users (read: not enterprises) it’s usually safe to wait a few days until after the patches are released, so that Microsoft has time to iron out any kinks in the new armor.

But before you update, please make sure you have backed up your system and/or important files. It’s not uncommon for a Windows update package to hose one’s system or prevent it from booting properly, and some updates have been known to erase or corrupt files.

So do yourself a favor and backup before installing any patches. Windows 10 even has some built-in tools to help you do that, either on a per-file/folder basis or by making a complete and bootable copy of your hard drive all at once.

And if you wish to ensure Windows has been set to pause updating so you can back up your files and/or system before the operating system decides to reboot and install patches on its own schedule, see this guide.

As always, if you experience glitches or problems installing any of these patches this month, please consider leaving a comment about it below; there’s a better-than-even chance other readers have experienced the same and may chime in here with some helpful tips.

Additional reading:

Martin Brinkman’s always comprehensive take.

The SANS Internet Storm Center no-frills breakdown of the fixes.