[German]The cumulative security updates released for Windows on April 14, 2024, are causing some issues. I have received several user reports indicating that users are unable to log in after installing the April 2026 updates. This affects Windows Server, but likely also Windows 11 clients (though that may be a different issue).
Microsoft updated the Media Creation Tool (MCT), version 10.0.26100.7019, on April 17, 2026, regarding the downloaded installation images. When creating a USB installation medium, Windows 11 25H2 Build 26200.8246 is now downloaded. This build includes the security update KB5083769 from April 14, 2026. (via)
[German]The security update KB5082063, released on April 14, 2026, for Windows Server 2025, causes installation error 0x800F0983 on some systems. In addition, the April 2026 updates caused reboot errors on domain controllers running Windows Server 2016–2026, Microsoft released out-of-band updates (including KB5091157) on April 19, 2026, to resolve installation error 0x800F0983 and the reboot error.
I have received several error reports related to the cumulative update KB508206, released on April 14, 2024, for Windows Server 2025. In some environments, the installation of this update fails with error code 0x80073712. Other machines fail with installation error 0x800F0983. Microsoft has confirmed the latter installation error; and I got an explanation for install error 0x80073712 (blame legacy Windows Media Player app).
[German]The cumulative updates released on April 14, 2026, for Windows Server 2016 through Windows Server 2025 (e.g., KB508206 for Windows Server 2025) cause domain controllers to reboot under certain conditions. I got some reports from my German blog readers during the last hours.
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There are several critical vulnerabilities in Microsoft Defender, that put Windows systems at risk. A security researcher has published an 0-day-exploit named BlueHammer on April 3, 2026, that has been patched on April 14, 2026. But there is still an unpatched vulnerability, where the security researcher has published the RedSun exploit. And ther is UnDefend, allowing to stop Windows Defender.
[German]On April 14, 2026 (Patch Day), Microsoft released a fix for Remote Desktop to protect RDP connections against phishing attacks. Users now see a warning message when establishing an RDP connection. This has caused a lot of confusion and issues. I've written a follow-up article providing an overview of the situation, including workarounds. And there are many user comments outlining more insights. Details may be read at my German blog post [use the build-in translator to switch the language].
[English]The security updates KB5083769 and KB5082052 for Windows 11, released on April 14, 2026, are causing BitLocker issues. Microsoft has since confirmed this in updates to the support articles. However, the prompt for the BitLocker recovery key only occurs in specific configurations that are not enabled by default. Details may be read at my German blog post [use the build-in translator to switch the language].
[German]Microsoft has announced an extension of the Extended Security Update (ESU) program for certain legacy software. This includes Microsoft Exchange 2016/2019 and Skype for Business Server, for which ESU "Period 2" is now being launched. This means that organizations can purchase an ESU extension for an additional six months. Details may be read within my German blog post [use the build-in tranlator to switch the language].
On April 14, 2026 (the second Tuesday of the month, Microsoft's Patch Tuesday), Microsoft released cumulative updates for the still-supported client operating system versions of Windows 10 (with an ESU license) and Windows 11. Microsoft has also released security updates for supported Windows Server versions and for Office as well.
MVP:
2013 – 2016
WIMVP:
2017 – 2020
