Microsoft releases urgent updates to fix RDP failures in Windows and Windows Server

Systems and published out-of-band updates

The table summarises the six packages covered by this notice. Confirm the version and build before installing any of them.

Microsoft’s support pages are the reference for prerequisites, known issues and installation methods. A version appearing in this table does not by itself confirm that a device is affected.

What happens with Remote Desktop and RDS

In an infrastructure that centralises applications or workplaces through RDS, an authentication failure or an unresponsive console can prevent users from reaching their desktop even while the server remains powered on. The priority is to distinguish an issue introduced by the update from network, licensing, profile or capacity problems.

Checks should include system logs, the installed build, when symptoms first appeared and a controlled access test. Uninstalling security updates without analysis may restore operations in the short term, but it can also reopen fixed vulnerabilities; the corresponding OOB update is the route documented by Microsoft.

Hyper-V Plan 9 and multichannel USB audio

Plan 9 enables folder sharing between the host and certain Linux virtual machines on Hyper-V. The fixed error could prevent those folders from mounting and affect processes that depend on that exchange. Post-update validation should check not only that the virtual machine starts, but also that shared paths are available again and applications can access them.

Microsoft also documents issues with multichannel USB Audio Class 1.0 devices on certain versions. This is a narrower issue, but it may matter in meeting rooms, audiovisual workstations or devices using audio interfaces compatible with this class.

Recommended action plan

The aim is not to install blindly, but to reduce exposure time without introducing a second incident. A short, documented procedure allows teams to act quickly while retaining recovery capability.

1. 1.Inventory Windows and Windows Server devices, including their version, build and active features.
2. 2.Identify RDS servers, Hyper-V hosts using Plan 9 folders and devices with multichannel USB audio that may be within scope.
3. 3.Check Microsoft’s official support pages and select only the KB corresponding to each version.
4. 4.Confirm a recoverable backup and agree the intervention window before changing production.
5. 5.Apply the update, restart where required, and validate RDP access, sessions, licensing, services, shared storage and affected peripherals.
6. 6.Document the result and maintain enhanced monitoring after the change.

What this incident teaches about continuity

A virtual desktop platform concentrates the work of many users. That concentration simplifies management, but it requires patching, backups, monitoring and access testing to be treated as one continuity process rather than independent tasks.

The organisation should know who authorises an urgent update, which backup enables rollback, how the service is tested with a limited group and which temporary alternative exists if remote access fails. These decisions should be prepared before the next critical update.

Official sources and documentation consulted

The pages linked below are the primary technical references. The information was consulted on 18 September 2026 and may subsequently be updated by Microsoft.

• Microsoft Support: KB5129236 — Windows 10 21H2 and 22H2
• Microsoft Support: KB5129195 — Windows 11 24H2 and 25H2
• Microsoft Support: KB5129194 — Windows 11 26H1
• Microsoft Support: KB5129238 — Windows Server 2019 and Windows 10 1809
• Microsoft Support: KB5129237 — Windows Server 2022
• Microsoft Support: KB5129235 — Windows Server 2025
• RedesZone: News report summarising the urgent updates

Frequently Asked Questions

Are all Windows devices affected?

No. The impact depends on the version, build, installed updates and configuration. Each device must be compared with the official support page for the relevant KB and with the symptoms observed.

What is a Microsoft out-of-band update?

It is an update released outside the regular monthly schedule to resolve an issue that requires an early correction. It should be assessed and installed with the same version control, backup and validation applied to any production change.

Should the September security update be uninstalled?

Not as a general measure. Uninstalling a security update can reopen vulnerabilities. If an issue exists, identify the affected system and apply the corrective update documented by Microsoft, with a recovery plan available.

Is a restart required after installing these KBs?

The need for and behaviour of the restart must be checked on the official support page and on the specific system. For production servers, plan an intervention window and validate services after it is complete.

How should an RDS server be validated after patching?

Check sign-in, session creation and closure, published applications, profiles, licensing, printing and access to required resources. Events and monitoring should also be reviewed during the period following the change.