Windows administrators report that the September 2026 cumulative updates can cause Remote Desktop Services (RDS) to hang or crash on Windows Server 2019, 2022, and 2025. Microsoft’s release notes separately confirm Remote Desktop problems in Windows Server 2016, including broken audio redirection, while the updates also address a critical RDS remote-code-execution flaw.

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A new Microsoft Defender zero-day called ShieldCrash can reportedly read arbitrary files as SYSTEM on fully patched Windows 10, Windows 11, and Windows Server systems. The proof of concept targets an incomplete fix for ShieldBreak, patched in September, and could potentially be expanded into a full SYSTEM privilege-escalation exploit.

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CompatTelRunner.exe is a Windows Compatibility Appraiser process. It runs diagnostic checks to determine whether a device’s hardware, drivers, and installed applications are compatible with upcoming Windows feature upgrades or cumulative updates. Microsoft has confirmed that the August 2026 security updates can cause recurring `0xc0000409` crashes in `CompatTelRunner.exe` on Windows Server 2016. The issue affects physical servers and virtual machines, including VMware and Azure deployments, but does not currently impair system functionality.

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Windows Server 2025 administrators may need to disable Lock Pages in Memory (LPIM) to stop SQL Server crashes linked to a change in the system’s memory-management behavior. Microsoft has not yet released a permanent fix for applications using Address Windowing Extensions (AWE), so disabling LPIM remains a potentially costly workaround.

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Microsoft will significantly tighten Windows Hardware Compatibility Program (WHCP) driver signing from March 2027. Drivers targeting Windows 11 25H2 or later and Windows Server 2025 or later will need validated Software Bill of Materials (SBOM) and Vulnerability Exploitability Exchange (VEX) files, while submissions will also need to target relatively modern hardware.

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