August updates trigger 0xc0000409 errors on Windows Server 2016
Recorded: Sept. 8, 2026, 4:10 p.m.
| Original | Summarized |
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Microsoft has issued a service alert indicating that August 2026 security updates may trigger 0xc0000409 errors on Windows Server 2016 systems, specifically when the Compatibility Appraiser diagnostic service is enabled. On affected systems, users will observe the CompatTelRunner.exe (Compatibility Appraiser Telemetry Runner) process crashing. This issue stems from Microsoft Compatibility Appraiser, which governs CompatTelRunner and functions as a Windows Compatibility Telemetry component responsible for checking if hardware and software meet the prerequisites for major Windows cumulative updates or feature upgrades. Microsoft noted that this known issue impacts both physical devices and virtual machine environments, including those running VMware and Azure platforms. Although these recurring failures in CompatTelRunner.exe may generate Application event log entries with exception code 0xc0000409, Microsoft stated that they do not affect device functionality. The associated warnings can be temporarily disregarded until a permanent resolution is released in a future update. Microsoft is currently working on a fix that will be included in a subsequent Windows update, though no timeline for the permanent solution has yet been provided. This situation relates to previous known issues where Microsoft fixed problems affecting June 2026 security updates and warnings about application crashes in Windows Server 2025 resulting from recent memory management changes affecting applications utilizing Address Windowing Extensions (AWE), which allows them to use more than four gigabytes of physical memory within a three-two bit virtual address space. When these memory management issues occur, impacted systems can experience memory corruption errors, access violation exceptions with error code 0xC0000005, SQL Server crash dumps, and unexpected stopping or restarting of SQL Server services. Furthermore, the text references data concerning general security posture, noting that once attackers possess valid credentials, prevention measures sharply decrease, as only thirty-seven percent of their actions are blocked, and the Blue Report 2026 measures defenses across customer production environments. |