Windows Authentication Failures Due to Duplicate Security Identifiers
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Windows updates released since August 29, 2025, have introduced authentication failures on systems with duplicate Security Identifiers (SIDs). These updates enforce stricter SID checks, causing Kerberos and NTLM authentication to fail on affected devices. The issue impacts Windows 11 (24H2 and 25H2) and Windows Server 2025, leading to various login and access problems. Duplicate SIDs often result from improperly cloned or duplicated Windows installations. Microsoft recommends rebuilding affected systems using supported cloning methods or applying a temporary Group Policy fix obtained through Microsoft Support.
Timeline
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21.10.2025 19:56 1 articles · 23h ago
Windows updates released since August 29, 2025, cause authentication failures due to duplicate SIDs
Windows updates released since August 29, 2025, enforce stricter SID checks, leading to authentication failures on devices with duplicate SIDs. This issue impacts Windows 11 24H2, Windows 11 25H2, and Windows Server 2025. Affected systems experience various login and access problems, including failed remote desktop connections and 'access denied' errors. Duplicate SIDs are often created when cloning or duplicating Windows installations without using the Sysprep tool. Microsoft recommends rebuilding affected systems using supported cloning methods or applying a temporary Group Policy fix.
Show sources
- Microsoft: Recent Windows updates cause login issues on some PCs — www.bleepingcomputer.com — 21.10.2025 19:56
Information Snippets
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Security Identifiers (SIDs) are unique alphanumeric strings used by Windows to manage user accounts, groups, and computer accounts.
First reported: 21.10.2025 19:561 source, 1 articleShow sources
- Microsoft: Recent Windows updates cause login issues on some PCs — www.bleepingcomputer.com — 21.10.2025 19:56
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Windows updates released on and after August 29, 2025, include stricter SID checks that cause authentication failures on devices with duplicate SIDs.
First reported: 21.10.2025 19:561 source, 1 articleShow sources
- Microsoft: Recent Windows updates cause login issues on some PCs — www.bleepingcomputer.com — 21.10.2025 19:56
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Affected systems include Windows 11 24H2, Windows 11 25H2, and Windows Server 2025.
First reported: 21.10.2025 19:561 source, 1 articleShow sources
- Microsoft: Recent Windows updates cause login issues on some PCs — www.bleepingcomputer.com — 21.10.2025 19:56
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Authentication failures can lead to issues such as failed remote desktop connections and 'access denied' errors.
First reported: 21.10.2025 19:561 source, 1 articleShow sources
- Microsoft: Recent Windows updates cause login issues on some PCs — www.bleepingcomputer.com — 21.10.2025 19:56
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Duplicate SIDs are often created when cloning or duplicating Windows installations without using the Sysprep tool.
First reported: 21.10.2025 19:561 source, 1 articleShow sources
- Microsoft: Recent Windows updates cause login issues on some PCs — www.bleepingcomputer.com — 21.10.2025 19:56
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Microsoft recommends rebuilding systems with duplicate SIDs using supported cloning methods.
First reported: 21.10.2025 19:561 source, 1 articleShow sources
- Microsoft: Recent Windows updates cause login issues on some PCs — www.bleepingcomputer.com — 21.10.2025 19:56
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A temporary fix involves installing and configuring a special Group Policy obtained through Microsoft Support.
First reported: 21.10.2025 19:561 source, 1 articleShow sources
- Microsoft: Recent Windows updates cause login issues on some PCs — www.bleepingcomputer.com — 21.10.2025 19:56