Microsoft’s September 2026 Patch Tuesday addresses 964 CVEs, including 104 rated Critical and 860 rated Important, making it the company’s largest Patch Tuesday release on record.

Microsoft lists 974 CVEs in its full September security release. However, 10 of those affect cloud services or involve fixes that Microsoft applies itself, leaving 964 vulnerabilities that customers need to patch.

The release includes fixes for two actively exploited Windows zero-days. Both are local elevation-of-privilege vulnerabilities that could allow an attacker who already has access to a device to gain SYSTEM privileges. Neither provides remote access by itself, but SYSTEM-level access is valuable to malware operators after they gain an initial foothold through phishing, stolen credentials, or another method.

How to apply patches and check if you’re protected

These updates fix security problems and help keep your Windows PC protected. Here’s how to make sure you’re up to date:

• Click the Start button, then open Settings.
• Select Windows Update (usually at the bottom of the menu on the left).
• Click Check for updates. Windows will search for the latest security updates. If you’ve enabled Get the latest updates as soon as they’re available under More options, you may be prompted to restart immediately to complete the update. Otherwise, continue to the next step.

• If updates are available, they’ll start downloading automatically. When they’re ready, click Install or Restart now if prompted. Your computer may need a restart to finish the update.
• After restarting, go back to Windows Update and check again. If it says You’re up to date, you’re all set.
  

Technical details

The unusually large batch also includes high-severity remote-code-execution vulnerabilities in Windows DNS Server and Remote Desktop Services, as well as fixes affecting Exchange Server, SharePoint, SQL Server, Office, and core Windows components.

Let’s take a closer look at the two zero-day vulnerabilities. Microsoft classifies a vulnerability as a zero-day if it was publicly disclosed or actively exploited before an official fix became available.

The first is a Windows Update Stack elevation-of-privilege (EoP) vulnerability with a CVSS score of 7.8 out of 10, tracked as CVE-2026-81963. The description says:

“Improper link resolution before file access (‘link following’) in Windows Update Stack allows an authorized attacker to elevate privileges locally.”

This means Windows can be persuaded to open or modify the wrong file because it follows a shortcut-like pointer without properly checking where that pointer leads. Microsoft says attackers exploited the bug before a patch was available.

The second zero-day, tracked as CVE-2026-85880, also has a CVSS score of 7.8 out of 10. Microsoft describes it as:

“heap-based buffer overflow in Windows ALPC allows an authorized attacker to elevate privileges locally.”

Microsoft says an attacker who can execute code in a low-privilege AppContainer could exploit the vulnerability locally to escape the sandbox and elevate their privileges on the affected system. No additional user interaction is required.

Windows ALPC is an internal messaging system in the Windows operating system that allows different programs on the same computer to communicate with each other quickly.

A buffer overflow occurs when an area of memory within a software application reaches its boundary and data spills into an adjacent memory region. The heap is a region of memory used for dynamic memory allocation.

These are not the kinds of bugs a typical victim triggers merely by opening a malicious document or visiting a website. But local privilege escalation is a critical part of many attack chains: After malware runs with limited rights, a SYSTEM-level exploit can help an intruder disable defenses, access protected data, establish persistence, or move through a network.

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Microsoft Corp. today issued updates to plug at least 974 security holes in its Windows operating systems and other software, by far its biggest single patch batch ever. Microsoft says artificial intelligence is helping to speed the discovery of vulnerabilities, but security experts warn that many organizations already are struggling to prioritize the more human-intensive endeavor of testing and deploying so many fixes each month.

Image: Shutterstock.com, Kirill Makarov.

This month’s patch bundle obliterates the software giant’s previous record set in July, when it released updates for at least 570 security vulnerabilities. September’s Patch Tuesday brings this year’s total to more than 2,600, more than twice Microsoft’s previous record-setting patch year in 2020 (1,245) and with three more months to go.

There are two “zero-day” flaws fixed this month that are being actively exploited: both CVE-2026-81963 and CVE-2026-85880 allow an attacker to elevate their privileges on Windows system.

Fully 113 of the bugs addressed today earned Microsoft’s “critical” rating, meaning they could be abused by malware or miscreants to seize control over a vulnerable Windows machine with little or no help from the user.

Among the more serious critical flaws this month is CVE-2026-69730, a DNS weakness present in Windows Server 2012 onward and on Windows 10. Microsoft warns that an unauthenticated attacker could leverage this weakness simply by sending a specially crafted packet to an affected system, and that it is likely to be exploited.

Also scary is CVE-2026-69829, a critical, remote code execution flaw in the Windows Shell. This vulnerability has a CVSS base score of 9.8 (10 is the most severe), and can be exploited with low attack complexity, no privileges, and no user interaction.

Microsoft’s summary of the security updates released today. Image: msrc.microsoft.com.

Microsoft is hardly alone in shipping monster patch bundles lately. Many other large software companies, including Adobe, Cisco, Google, Mozilla and Oracle, all have recently credited AI-assisted research with increasing their patch cadence and volume (Google said today it is now going to ship security updates every two weeks).

Tyler Reguly, associate director of security research and development at Fortra, said one core challenge with deploying Windows updates is that they need to be tested before being installed across an organization because not all third-party software works seamlessly in the face of changes to the underlying operating system.

“It’s time to put our CISOs and CSOs on notice,” Reguly said. “How are you helping your teams through these difficult times? Do you have your teams deploy after hours and on weekends to avoid disruption to the business environment? Do you reward them for that effort? Time to dig into your budget and buy dinner for your teams that are working on Saturday to get patches rolled out before users return to work on Monday.”

Satnam Narang is senior staff research engineer at Tenable. Narang said it’s important to recognize that while the number of vulnerabilities being patched by Microsoft is rising, the number of flaws that can and will affect most organizations remains quite low.

“AI-assisted vulnerability discovery in 2026 is creating larger haystacks, but it isn’t finding more needles,” he said. “It’s critical that organizations understand which vulnerabilities actually apply to them, whether they pose a threat by being reachable and exploitable, and prioritize remediation based on this risk context.”

Of course, regular Windows users don’t need to test patches before deploying them, but they still need to open Windows Update periodically or else assent to the program’s nag notices about pending updates. And at the rate these Windows patch releases are ballooning in size, it’s probably best not to let them pile up month after month.

Enterprise Windows admins will want to keep an eye on askwoody.com for news of any updates that appear to be causing problems. As always, the SANS Internet Storm Center has a per-patch breakdown ordered by severity and urgency.