Microsoft Patch Tuesday, September 2021 Edition

Microsoft today pushed software updates to plug dozens of security holes in Windows and related products, including a vulnerability that is already being exploited in active attacks. Also, Apple has issued an emergency update to fix a flaw that’s reportedly been abused to install spyware on iOS products, and Google‘s got a new version of Chrome that tackles two zero-day flaws. Finally, Adobe has released critical security updates for Acrobat, Reader and a slew of other software.

Four of the flaws fixed in this patch batch earned Microsoft’s most-dire “critical” rating, meaning they could be exploited by miscreants or malware to remotely compromise a Windows PC with little or no help from the user.

Top of the critical heap is CVE-2021-40444, which affects the “MSHTML” component of Internet Explorer (IE) on Windows 10 and many Windows Server versions. In a security advisory last week, Microsoft warned attackers already are exploiting the flaw through Microsoft Office applications as well as IE.

The critical bug CVE-2021-36965 is interesting, as it involves a remote code execution flaw in “WLAN AutoConfig,” the component in Windows 10 and many Server versions that handles auto-connections to Wi-Fi networks. One mitigating factor here is that the attacker and target would have to be on the same network, although many systems are configured to auto-connect to Wi-Fi network names with which they have previously connected.

Allan Liska, senior security architect at Recorded Future, said a similar vulnerability — CVE-2021-28316 — was announced in April.

“CVE-2021-28316 was a security bypass vulnerability, not remote code execution, and it has never been reported as publicly exploited,” Liska said. “That being said, the ubiquity of systems deployed with WLAN AutoConfig enabled could make it an attractive target for exploitation.”

Kevin Breen of Immersive Labs calls attention to several “privilege escalation” flaws fixed by Microsoft this month, noting that while these bugs carry lesser severity ratings, Microsoft considers them more likely to be exploited by bad guys and malware.

“CVE-2021-38639 and CVE-2021-36975 have also been listed as ‘exploitation more likely’ and together cover the full range of supported Windows versions,” Breem wrote. “I am starting to feel like a broken record when talking about privilege escalation vulnerabilities. They typically have a lower CVSS score than something like Remote Code Execution, but these local exploits can be the linchpin in the post-exploitation phases of an experienced attacker. If you can block them here you have the potential to significantly limit their damage. If we assume a determined attacker will be able to infect a victim’s device through social engineering or other techniques, I would argue that patching these is even more important than patching some other Remote Code execution vulnerabilities.”

Apple on Monday pushed out an urgent security update to fix a “zero-click” iOS vulnerability (CVE-2021-30860) reported by researchers at Citizen Lab that allows commands to be run when files are opened on certain Apple devices. Citizen Lab found that an exploit for CVE-2021-30860 was being used by the NSO Group, an Israeli tech company whose spyware enables the remote surveillance of smartphones.

Google also released a new version of its Chrome browser on Monday to fix nine vulnerabilities, including two that are under active attack. If you’re running Chrome, keep a lookout for when you see an “Update” tab appear to the right of the address bar. If it’s been a while since you closed the browser, you might see the Update button turn from green to orange and then red. Green means an update has been available for two days; orange means four days have elapsed, and red means your browser is a week or more behind on important updates. Completely close and restart the browser to install any pending updates.

As it usually does on Patch Tuesday, Adobe also released new versions of Reader, Acrobat and a large number of other products. Adobe says it is not aware of any exploits in the wild for any of the issues addressed in its updates today.

For a complete rundown of all patches released today and indexed by severity, check out the always-useful Patch Tuesday roundup from the SANS Internet Storm Center. And it’s not a bad idea to hold off updating for a few days until Microsoft works out any kinks in the updates: AskWoody.com usually has the lowdown on any patches that are causing problems for Windows users.

On that note, 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.

If you experience glitches or problems installing any of these patches this month, please consider leaving a comment about it below; there’s a decent chance other readers have experienced the same and may chime in here with useful tips.