Windows SMB Server Elevation of Privilege Vulnerability
This high-severity Microsoft Server advisory covers CVE-2026-20921 affecting Windows Server 2008 R2 Service Pack 1 (Server Core installation), Windows Server 2008 Service Pack 2 (Server Core installation), Windows Server 2012 (Server Core installation).
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Summary
Concurrent execution using shared resource with improper synchronization ('race condition') in Windows SMB Server allows an authorized attacker to elevate privileges over a network.
Affected products named by the advisory: Windows Server 2008 R2 Service Pack 1; Windows Server 2008 R2 Service Pack 1 (Server Core installation); Windows Server 2008 Service Pack 2; Windows Server 2008 Service Pack 2 (Server Core installation); and 12 more.
Affected products named by the advisory: Windows Server 2012 (Server Core installation); Windows Server 2012 R2 (Server Core installation); Windows Server 2016 (Server Core installation); Windows Server 2019 (Server Core installation); and 2 more.
- Windows 10 Version 1607 10.0.14393.0 before 10.0.14393.8783
- Windows 10 Version 1809 10.0.17763.0 before 10.0.17763.8276
- Windows 10 Version 21H2 10.0.19044.0 before 10.0.19044.6809
- Windows 10 Version 22H2 10.0.19045.0 before 10.0.19045.6809
- Windows 11 version 23H2 10.0.22631.0 before 10.0.22631.6491
- Windows 11 Version 23H2 10.0.22631.0 before 10.0.22631.6491
- Windows 11 Version 24H2 10.0.26100.0 before 10.0.26100.7623
- Windows 11 Version 25H2 10.0.26200.0 before 10.0.26200.7623
- Windows Server 2008 R2 Service Pack 1 6.1.7601.0 before 6.1.7601.28117
- Windows Server 2008 R2 Service Pack 1 (Server Core installation) 6.1.7601.0 before 6.1.7601.28117
- Windows Server 2008 Service Pack 2 6.0.6003.0 before 6.0.6003.23717
- Windows Server 2008 Service Pack 2 (Server Core installation) 6.0.6003.0 before 6.0.6003.23717
Official advisory · high-confidence parse· fetched 2 hours ago·verify at source
- 10.0.14393.8783
- 10.0.17763.8276
- 10.0.19044.6809
- 10.0.19045.6809
- 10.0.22631.6491
- 10.0.26100.7623
- 10.0.26200.7623
- 6.1.7601.28117
- 6.0.6003.23717
- 6.2.9200.25868
- 6.3.9600.22968
- 10.0.20348.4648
Official advisory · high-confidence parse· fetched 2 hours ago·verify at source
Mitigation
Upgrade to a fixed release: 10.0.14393.8783, 10.0.17763.8276, 10.0.19044.6809, 10.0.19045.6809, 10.0.22631.6491, 10.0.26100.7623. That is the remediation for this advisory.
The vendor advisory may list additional interim mitigations or workarounds not captured here — review it before change work.
Official advisory · high-confidence parse· fetched 2 hours ago·verify at source
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