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Domain Controller

Windows Server vulnerability can grant system privileges with just a malformed packet — domain controllers are being exploited in the wild
Winsage
June 1, 2026

Windows Server vulnerability can grant system privileges with just a malformed packet — domain controllers are being exploited in the wild

Microsoft is facing scrutiny due to a critical remote execution vulnerability, CVE-2026-41089, rated at 9.8, affecting Windows Server domain controllers from version 2012 onward. This vulnerability allows unauthenticated users on the same network to send malformed UDP packets to a domain controller, potentially granting unauthorized system access or causing a reboot, leading to denial-of-service scenarios. The vulnerable service is Netlogon, and there are no immediate mitigations available; patches will be released on May 12. The vulnerability could allow attackers to create multiple accounts with various access levels, compromising the security of entire networks. Cybersecurity experts recommend patching all linked domain controllers simultaneously. The vulnerability is caused by a buffer overflow in the Netlogon service due to a field in a network packet exceeding its expected size. A GitHub repository exists with proof-of-concept code that can crash the LSASS service. Additionally, Microsoft is in conflict with security researcher Chaotic Eclipse, who has published zero-day exploits following a breakdown in negotiations.
Critical Windows Netlogon RCE flaw now exploited in attacks
Winsage
June 1, 2026

Critical Windows Netlogon RCE flaw now exploited in attacks

The Centre for Cybersecurity Belgium (CCB) has warned about the exploitation of a critical vulnerability in Windows Netlogon, identified as CVE-2026-41089, which allows remote code execution on domain controllers without prior access or authentication. This vulnerability, characterized as a stack-based buffer overflow, was patched by Microsoft during the May 2026 Patch Tuesday. The CCB emphasized the urgency of patching vulnerable servers, noting that the vulnerability is actively being exploited. The CVSS score for this vulnerability is 9.8. Further details on the ongoing attacks have not been disclosed, and Microsoft has not updated its advisory on the vulnerability.
Microsoft tests the 15-character limit of Windows Server admins' patience
Winsage
May 28, 2026

Microsoft tests the 15-character limit of Windows Server admins’ patience

Windows Server 2016 has a bug introduced by the May 12 security update that affects servers with hostnames exactly 15 characters long, causing errors in domain controller discovery. Specifically, calling the DCLocator results in an ERRORINVALIDPARAMETER, hindering applications and tools from locating a domain controller. This issue impacts features like Distributed File System (DFS) Namespace management. Microsoft has not provided a workaround but suggests changing the hostname length. Windows Server 2016 is officially supported until January 12, 2027, with extended support options available. Despite representing only 2.2 percent of all Windows devices, it accounts for 20.3 percent of all servers. Additionally, the May 2026 security update has caused installation failures on some Windows 11 devices due to insufficient EFI System Partition size.
Windows Server 2016 Update: Disastrous Bug Breaks AD
Winsage
May 28, 2026

Windows Server 2016 Update: Disastrous Bug Breaks AD

Microsoft released a mandatory patch (KB5087537) for Windows Server 2016 to enhance cryptographic layers and address critical vulnerabilities. This update is essential for organizations using legacy workloads, as mainstream support ended in January 2022, but extended support continues until January 12, 2027. The patch aims to prepare systems for the expiration of Windows Secure Boot certificates in June 2026, which, if not updated, could compromise security and expose systems to malware. The update uses a phased deployment model and includes a new SecureBoot folder to assist IT professionals in managing certificate status. It also addresses various quality-of-life issues, including bugs affecting Remote Desktop Connection and authentication errors with Microsoft services. However, a significant issue arises when the host server name is exactly 15 characters long, causing failures in the domain controller discovery process and obstructing critical operations. This bug is linked to the historical 15-character limit of NetBIOS, which affects the Active Directory lookup mechanism. Microsoft has acknowledged the issue but has not provided a timeline for a fix, leaving administrators to either rename servers or uninstall the update. As the Secure Boot deadline approaches, IT departments must carefully assess their environments to avoid disruptions while ensuring security compliance.
Windows Server 2016 fails to find domain controller
Winsage
May 28, 2026

Windows Server 2016 fails to find domain controller

Microsoft has acknowledged an issue with the May 2026 security update for Windows Server 2016, affecting systems with hostnames of exactly 15 characters, which leads to failed domain controller (DC) lookups. The error occurs during DC lookups, specifically returning the error code ERRORINVALIDPARAMETER. Servers with 14 or 16 character hostnames are not affected. Administrators may face challenges with DFS Namespace management and other functions reliant on DC access. Microsoft is investigating the issue but has not provided a timeline for a fix. Windows Server 2016's mainstream support ended in January 2022, but extended support will continue until January 2027.
Microsoft: Domain Controller lookup may fail on Windows Server 2016
Winsage
May 26, 2026

Microsoft: Domain Controller lookup may fail on Windows Server 2016

Microsoft has acknowledged an issue affecting Windows Server 2016 systems related to domain controller lookups after the installation of the KB5087537 security update released in May 2026. The problem occurs specifically for devices with hostnames that are exactly 15 characters long, causing domain controller discovery to fail and resulting in an ERRORINVALIDPARAMETER during DCLocator calls. This issue may disrupt administrative operations that depend on domain controller lookups, such as DFS Namespace management. Microsoft is investigating the issue but has not provided a timeline for resolution.
Emergency Update for Windows Server Following Reboot Issues
Winsage
April 20, 2026

Emergency Update for Windows Server Following Reboot Issues

Microsoft has released emergency updates for various versions of Windows Server due to issues arising from the April 2026 Patch Tuesday security updates. A significant problem was a reboot loop affecting domain controllers caused by crashes of the Local Security Authority Subsystem Service (LSASS), which disrupted authentication services. This issue was especially problematic during the setup of new domain controllers. Additionally, some Windows Server 2025 systems encountered difficulties in installing the security update KB5082063. The out-of-band update (KB5091157) for Windows Server 2025 addresses both the installation failure and the domain controller restart issue. Other updates targeting the domain controller restart problem were released for additional supported Windows Server versions. Microsoft has introduced an out-of-band update for seven versions, including KB5091157 for Windows Server 2025 and KB5091571 for Windows Server, version 23H2. Furthermore, some Windows Server 2025 devices may boot into BitLocker recovery mode after the update, requiring users to enter a BitLocker recovery key.
Microsoft releases emergency updates to fix Windows Server issues
Winsage
April 20, 2026

Microsoft releases emergency updates to fix Windows Server issues

Microsoft has confirmed that some administrators are experiencing difficulties installing the KB5082063 security update on Windows Server 2025. This month's Patch Tuesday updates have caused certain Windows servers, especially those with domain controller roles, to enter a restart loop due to failures in the Local Security Authority Subsystem Service (LSASS). Microsoft has released emergency out-of-band updates, including KB5091157 for Windows Server 2025, to address both the installation failure and the restart issues. Additionally, some Windows Server 2025 devices may boot into BitLocker recovery mode after installing the KB5082063 update. A bug affecting Windows Server 2019 and Windows Server 2022 that caused unexpected upgrades to Windows Server 2025 has also been resolved. Microsoft has issued various emergency updates throughout the year to address other issues, including a Bluetooth device visibility bug and vulnerabilities in the Routing and Remote Access Service (RRAS).
Microsoft's April patch puts Windows domain controllers into reboot loops — third known issue from KB5082063 is affecting Windows Server 2016 through 2025
Winsage
April 17, 2026

Microsoft’s April patch puts Windows domain controllers into reboot loops — third known issue from KB5082063 is affecting Windows Server 2016 through 2025

Microsoft has acknowledged that the April 2026 security update for Windows Server, patch KB5082063, has caused significant disruptions for some enterprise domain controllers, leading to continuous reboot cycles in non-Global Catalog domain controllers used in Privileged Access Management (PAM) deployments. This has resulted in the unavailability of Active Directory authentication and directory services on affected servers. Additionally, the installation of KB5082063 may fail on some Windows Server 2025 systems. This issue marks the third consecutive year that April security updates have caused problems for Windows Server domain controllers. In previous years, Microsoft issued emergency fixes for similar issues, including crashes and complications with NTLM authentication. Administrators currently have limited options, including delaying the update, isolating a test domain controller, or engaging with Microsoft Support for tailored mitigation steps.
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