Microsoft Fixes 974 Security Flaws In September Windows Update
Security researchers counted 974 vulnerabilities addressed in the release, including 113 rated critical. The update also includes fixes for two vulnerabilities that were already being exploited.
The unusually large number of fixes means Windows users and organisations should install the available security updates rather than delay them.
Microsoft Releases September Security Updates
Microsoft's September Patch Tuesday update was released on September 8, 2026.
The fixes cover Windows and several other Microsoft products and services. Researchers have described the release as the largest Patch Tuesday security update recorded by Microsoft.
The vulnerabilities include different types of security flaws, with elevation-of-privilege and remote-code-execution vulnerabilities among the major categories addressed in the update.
Two Vulnerabilities Were Already Being Exploited
One of the main concerns with this month's update is that two of the vulnerabilities had already been exploited before Microsoft released its fixes.
Both are elevation-of-privilege vulnerabilities affecting Windows. Such flaws can allow an attacker who has already gained access to a system to obtain higher levels of control.
The inclusion of actively exploited vulnerabilities makes installing the September security update particularly important for affected Windows systems.
113 Vulnerabilities Rated Critical
Among the vulnerabilities addressed this month, 113 were rated critical by Microsoft, according to security researchers tracking the release.
Critical vulnerabilities can present serious risks when exploited, particularly when they affect widely used software or can be used to execute malicious code.
The September update therefore covers more than routine bug fixes and includes security issues that require attention.
What Windows Users Should Do
Windows users should check for the latest available updates on their computers.
To check for updates on Windows 11:
- Open Settings.
- Select Windows Update.
- Click Check for updates.
- Download and install available updates.
- Restart the computer if required.
The exact update available will depend on the version of Windows installed on the device.
Why You Should Not Delay Windows Updates
Security updates are released to fix vulnerabilities that could potentially be used against computers.
Delaying updates leaves known security weaknesses unpatched for longer. This is particularly important when vulnerabilities are already being exploited.
For home users, keeping Windows updated is one of the simplest ways to maintain the security of a computer.
The Update Covers More Than Windows
Although Windows users are directly affected by the operating system updates, Microsoft's September security release covers a much wider range of products.
The September fixes also address vulnerabilities affecting products and services including Microsoft Office, Exchange Server, SharePoint Server, SQL Server and other Microsoft technologies.
This makes the update particularly important for businesses and organisations that rely on Microsoft's wider software ecosystem.
Microsoft Has Released A Record Number Of Fixes
The size of September's release stands out compared with Microsoft's previous monthly updates.
CrowdStrike counted 972 Microsoft vulnerabilities in the September release, while other security trackers reported 973 or 974 depending on how the vulnerabilities were counted.
Regardless of the slight difference in counting, security researchers agree that September's release represents an unusually large Microsoft security update.
Install The September Update
Windows users should check their devices for the September 2026 security updates and install them when available.
With two vulnerabilities already being exploited and more than 100 rated critical, leaving the updates pending for an extended period could expose systems to known security weaknesses.
For most users, checking Settings > Windows Update is the simplest way to see whether the latest security updates are ready to install.
