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Patch Tuesday

Patch Tuesday September 2026 – known issues, zero-days and what to do

On 8 Sep 2026 Microsoft fixed 998 vulnerabilities – critical: 131, already exploited (zero-days): 2. Known issues with the updates: 2 open, 2 with workaround, 3 fixed.

998vulnerabilities
131critical
2zero-days
7known issues

What to do now

Zero-days: already exploited

Critical vulnerabilities (60)

Show 54 more critical vulnerabilities

Updates (KB) of this month

KB numbers according to the Security Update Guide; known issues from our update issues – click a KB to see all its entries.

UpdateProduct familyVulnerabilitiesKnown issues
KB5124008Windows6075
KB5122871Windows6552
KB5122882Windows6192
KB5124012Windows1032
KB5129194Windows12
KB5122876Windows5941
KB5122880Windows5811
KB5122878Windows5481
KB5123099Windows811
KB5123065Windows71none known
KB5123066Windows71none known
KB5122773SQL Server52none known
Show 34 more updates
UpdateProduct familyVulnerabilitiesKnown issues
KB5122771SQL Server52none known
KB5122770SQL Server50none known
KB5122772SQL Server45none known
KB5122775SQL Server45none known
KB5122774SQL Server45none known
KB5002923Microsoft Office30none known
KB5002914Microsoft Office30none known
KB5002904Microsoft Office30none known
KB5122769SQL Server23none known
KB5122768SQL Server18none known
KB5002916Microsoft Office17none known
KB5002908Microsoft Office16none known
KB5121610Windows ESU (Extended Security Updates)9none known
KB5121609Windows ESU (Extended Security Updates)9none known
KB5121608Windows ESU (Extended Security Updates)9none known
KB5123301Microsoft Office9none known
KB5123287Microsoft Office9none known
KB5123300Microsoft Office9none known
KB5121611Windows ESU (Extended Security Updates)8none known
KB5002920Microsoft Office6none known
KB5126105Developer tools (.NET, Visual Studio …)6none known
KB5126106Developer tools (.NET, Visual Studio …)6none known
KB5126104Developer tools (.NET, Visual Studio …)5none known
KB5002910Microsoft Office5none known
KB5002919Microsoft Office3none known
KB5002912Microsoft Office2none known
KB5002913Microsoft Office2none known
KB5002644Microsoft Office2none known
KB5002898Microsoft Office2none known
KB5126049Developer tools (.NET, Visual Studio …)1none known
KB5126047Developer tools (.NET, Visual Studio …)1none known
KB5126051Developer tools (.NET, Visual Studio …)1none known
KB5123731Microsoft Dynamics1none known
KB4011160Microsoft Office1none known

Known issues with the updates

OpenKnown issueCommunity report

Windows 11/Server 2025: USB Audio Class 1.0 devices fail (Code 10) or give no sound

USB Audio Class 1.0 devices reportedly fail with Code 10 or produce no sound on Windows 11 and Windows Server 2025. This is reported by users, not yet confirmed by the vendor. No permanent fix has been found; a third-party page claims the Windows Server 2022 update KB5126655 fixes it, which is unverified.

Microsoft · Windows Server 2025, Windows 11 26H2/25H2/24H2, Windows Server 2019

WorkaroundKnown issue

Windows 11 26H2: USB audio devices might fail to start or produce no sound

Some USB Audio Class 1.0 devices might fail to start or produce no audio after installing Windows 11, version 26H2. Microsoft lists the same issue for other Windows client and server versions, where it originates from the September 8, 2026 security updates. For 26H2 the vendor status is Mitigated and a fix in a future Windows update is still being worked on.

Microsoft · Windows 11, Version 26H2

WorkaroundKnown issueCommunity report

Windows 11/10 ESU: File History shows false 'Reconnect your drive' after 8 Sep 2026 update

File History is reported to show a false 'Reconnect your drive' message after the 8 Sep 2026 update, and backups stop working. This is reported by users, not yet confirmed by the vendor. A fix is reported to be available with KB5124010, but one report says part of the problem persists.

Microsoft · Windows 11 23H2, 24H2, 25H2, 26H1 and Windows 10 ESU

FixedKnown issueCommunity report

Windows 11: Always On VPN failures from September updates fixed in KB5127936

Always On VPN profiles with automatic protocol selection or fallback (IKEv2 and SSTP) failed after the September 2026 Windows 11 updates. According to secondary sources and research notes, the optional preview update KB5127936 (28 Oct 2026) fixes this. We could not read the vendor page ourselves, so the details are not yet confirmed by a vendor source here.

Microsoft · Windows 11

FixedKnown issue

Windows 11 26H2: Domain-joined devices may lose their trust relationship with the domain

After installing Windows 11 version 26H2, Credential Guard protected machine accounts may lose their secure channel to an on-premises Active Directory domain. The cause is Machine Identity Isolation (MII), which Windows now honours; it is only supported with Windows Server 2025 domain controllers at Domain Functional Level 2025 or above. Microsoft has resolved the issue with updates released on 2026-09-22 and later.

Microsoft · Windows 11, Version 26H2

FixedKnown issue

Windows 11 26H2: October 2026 update fixes VPN, FSLogix and S2D issues; one extra restart possible

The October 2026 Windows security update was released on 2026-10-13 for all supported Windows versions. For Windows 11, version 26H2, it fixes several known problems: Always On VPN, a black screen in Azure Virtual Desktop with FSLogix, and tiered Storage Spaces Direct virtual disks. A limited number of devices may need one additional restart during installation because of the Secure Boot certificate update.

Microsoft · Windows 11

By product family

  • Windows705
  • Microsoft Office142
  • SQL Server62
  • Azure24
  • Developer tools (.NET, Visual Studio …)22
  • Other19
  • Windows ESU (Extended Security Updates)9
  • Apps5

More about this month

Where the information comes from

Fixed vulnerabilities, severity, zero-days and KB numbers come from the official Microsoft Security Update Guide (MSRC); known issues, workarounds and dated changes from our update issues, each with its source. “What to do now” is derived from this data using fixed rules, without AI.

Affected? We can help.

We check whether your systems are affected, apply workarounds properly and plan for dated changes in good time.

Get in touchAll known issues after updates