# Microsoft September 2026 security patch deployment

> Live situation record from CLSTR: https://clstr.news/situations/microsoft-september-2026-security-patch-deployment
> Updated: 2026-09-12T03:00:00.000Z. Sources: 29. Developments: 2.

In September 2026, Microsoft released a record-breaking batch of security patches, addressing between 966 and 974 vulnerabilities across its product suite. This massive deployment, the largest single patch batch in the company’s history, was attributed to the implementation of MDASH (Microsoft Security multi-model agentic scanning harness), an AI-driven system that uses automated agents to scan code and simulate attack scenarios.

The update addressed several critical issues, including 105 flaws classified as critical. This included two zero-day vulnerabilities (CVE-2026-81963 and CVE-2026-85880) affecting the Windows Update Stack and the Windows Advanced Local Procedure Call mechanism, which were being actively exploited in the wild to allow attackers to escalate privileges to the SYSTEM level.

Following the release, the deployment of the Windows 11 cumulative update (KB5124008) led to various technical malfunctions. Reported issues included Remote Desktop Protocol connection failures, Linux virtual machine directory sharing errors, and audio failures for certain USB devices on Windows 11 versions 24H2, 25H2, and 26H1. Other reported bugs included Explorer.exe crashes causing black screens and instability with certain graphics drivers. Microsoft has confirmed issues regarding Remote Desktop Services and Linux file sharing, advising users to complete security updates within three days to mitigate risks while investigations into the bugs continue.

## Claims

- Microsoft released a record-breaking batch of security patches in September 2026, addressing between 966 and 974 vulnerabilities. (corroborated by 7 sources)
- Two zero-day vulnerabilities, CVE-2026-81963 and CVE-2026-85880, were actively exploited by attackers before being patched. (corroborated by 5 sources)
- Of the vulnerabilities addressed in the September cycle, 105 were classified as critical. (corroborated by 3 sources)
- The surge in vulnerability discovery is attributed to the use of MDASH, an AI-driven multi-model agentic scanning harness. (corroborated by 2 sources)
- The KB5124008 update has caused functional issues, including audio failures for USB devices and Remote Desktop Service errors. (corroborated by 2 sources)
- Microsoft has updated its deployment recommendations, suggesting users install security updates within three days. (single source)

## Timeline

### 2026-09-12: Microsoft issues record-breaking security patches for Windows

Microsoft released a record-breaking September 2026 security update addressing nearly 1,000 vulnerabilities, including two actively exploited zero-days, using new AI-driven scanning tools.

8 sources. https://clstr.news/cluster/microsoft-releases-massive-security-update-amid-reports-of-new-windows-bugs

### 2026-09-07: Microsoft issues record 974 security patches, including two exploited zero-days

Microsoft released a record 974 security patches in September 2026, including 723 for Windows. Two zero-day vulnerabilities are being actively exploited to escalate system privileges.

21 sources. https://clstr.news/cluster/google-releases-chrome-updates-and-patches-security-vulnerabilities

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Cite as: Microsoft September 2026 security patch deployment. CLSTR, https://clstr.news/situations/microsoft-september-2026-security-patch-deployment