Microsoft Patches Six Zero-Day Security Holes

Microsoft today released another round of security updates for Windows operating systems and supported software, including fixes for six zero-day bugs that malicious hackers already are exploiting in active attacks.

June’s Patch Tuesday addresses just 49 security holes — about half the normal number of vulnerabilities lately. But what this month lacks in volume it makes up for in urgency: Microsoft warns that bad guys are leveraging a half-dozen of those weaknesses to break into computers in targeted attacks.

Among the zero-days are:

–CVE-2021-33742, a remote code execution bug in a Windows HTML component.
–CVE-2021-31955, an information disclosure bug in the Windows Kernel
–CVE-2021-31956, an elevation of privilege flaw in Windows NTFS
–CVE-2021-33739, an elevation of privilege flaw in the Microsoft Desktop Window Manager
–CVE-2021-31201, an elevation of privilege flaw in the Microsoft Enhanced Cryptographic Provider
–CVE-2021-31199, an elevation of privilege flaw in the Microsoft Enhanced Cryptographic Provider

Kevin Breen, director of cyber threat research at Immersive Labs, said elevation of privilege flaws are just as valuable to attackers as remote code execution bugs: Once the attacker has gained an initial foothold, he can move laterally across the network and uncover further ways to escalate to system or domain-level access.

“This can be hugely damaging in the event of ransomware attacks, where high privileges can enable the attackers to stop or destroy backups and other security tools,” Breen said. “The ‘exploit detected’ tag means attackers are actively using them, so for me, it’s the most important piece of information we need to prioritize the patches.”

Microsoft also patched five critical bugs — flaws that can be remotely exploited to seize control over the targeted Windows computer without any help from users. CVE-2021-31959 affects everything from Windows 7 through Windows 10 and Server versions 2008, 2012, 2016 and 2019.

Sharepoint also got a critical update in CVE-2021-31963; Microsoft says this one is less likely to be exploited, but then critical Sharepoint flaws are a favorite target of ransomware criminals.

Interestingly, two of the Windows zero-day flaws — CVE-2021-31201 and CVE-2021-31199 — are related to a patch Adobe released today for CVE-2021-28550, a flaw in Adobe Acrobat and Reader that also is being actively exploited.

“Attackers have been seen exploiting these vulnerabilities by sending victims specially crafted PDFs, often attached in a phishing email, that when opened on the victim’s machine, the attacker is able to gain arbitrary code execution,” said Christopher Hass, director of information security and research at Automox. “There are no workarounds for these vulnerabilities, patching as soon as possible is highly recommended.”

In addition to updating Acrobat and Reader, Adobe patched flaws in a slew of other products today, including Adobe Connect, Photoshop, and Creative Cloud. The full list is here, with links to updates.

The usual disclaimer:

Before you update with this month’s patch batch, please make sure you have backed up your system and/or important files. It’s not uncommon for Windows updates to hose one’s system or prevent it from booting properly, and some updates even 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.

For a quick visual breakdown of each update released today and its severity level, check out the this Patch Tuesday post from the SANS Internet Storm Center.