CVE-2026-20921: Windows SMB Server Elevation of Privilege Vulnerability

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-01-13 · updated 2026-07-30
Weakness: CWE-362

Description

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

Microsoft Windows 10 1607: before 10.0.14393.8783 — fixed in 10.0.14393.8783
Microsoft Windows 10: before 10.0.17763.8276 — fixed in 10.0.17763.8276
Microsoft Windows 10: before 10.0.19044.6809 — fixed in 10.0.19044.6809
Microsoft Windows 10: before 10.0.19045.6809 — fixed in 10.0.19045.6809
Microsoft Windows 11: before 10.0.22631.6491 — fixed in 10.0.22631.6491
Microsoft Windows 11: before 10.0.26100.7623 — fixed in 10.0.26100.7623
Microsoft Windows 11 25H2: before 10.0.26200.7623 — fixed in 10.0.26200.7623
Microsoft Windows Server 2008: r2-sp1
Microsoft Windows Server 2012: r2
Microsoft Windows Server 2016: before 10.0.14393.8783 — fixed in 10.0.14393.8783
Microsoft Windows Server 2019: before 10.0.17763.8276 — fixed in 10.0.17763.8276
Microsoft Windows Server 2022: before 10.0.20348.4648 — fixed in 10.0.20348.4648
Microsoft Windows Server 2022, 23H2 Edition (Server Core installation): before 10.0.25398.2092 — fixed in 10.0.25398.2092
Microsoft Windows Server 2025: before 10.0.26100.32230 — fixed in 10.0.26100.32230
Microsoft Windows 10 1607: from 10.0.14393.0 before 10.0.14393.8783 — fixed in 10.0.14393.8783
Microsoft Windows 10: from 10.0.17763.0 before 10.0.17763.8276 — fixed in 10.0.17763.8276
Microsoft Windows 10: from 10.0.19044.0 before 10.0.19044.6809 — fixed in 10.0.19044.6809
Microsoft Windows 10: from 10.0.19045.0 before 10.0.19045.6809 — fixed in 10.0.19045.6809
Microsoft Windows 11: from 10.0.22631.0 before 10.0.22631.6491 — fixed in 10.0.22631.6491
Microsoft Windows 11: from 10.0.26100.0 before 10.0.26100.7623 — fixed in 10.0.26100.7623
Microsoft Windows 11 25H2: from 10.0.26200.0 before 10.0.26200.7623 — fixed in 10.0.26200.7623
Microsoft Windows Server 2008 R2 Service Pack 1: from 6.1.7601.0 before 6.1.7601.28117 — fixed in 6.1.7601.28117
Microsoft Windows Server 2008 Service Pack 2: from 6.0.6003.0 before 6.0.6003.23717 — fixed in 6.0.6003.23717
Microsoft Windows Server 2012: from 6.2.9200.0 before 6.2.9200.25868 — fixed in 6.2.9200.25868
Microsoft Windows Server 2012 R2: from 6.3.9600.0 before 6.3.9600.22968 — fixed in 6.3.9600.22968
Microsoft Windows Server 2016: from 10.0.14393.0 before 10.0.14393.8783 — fixed in 10.0.14393.8783
Microsoft Windows Server 2019: from 10.0.17763.0 before 10.0.17763.8276 — fixed in 10.0.17763.8276
Microsoft Windows Server 2022: from 10.0.20348.0 before 10.0.20348.4648 — fixed in 10.0.20348.4648
Microsoft Windows Server 2022, 23H2 Edition (Server Core installation): from 10.0.25398.0 before 10.0.25398.2092 — fixed in 10.0.25398.2092
Microsoft Windows Server 2025: from 10.0.26100.0 before 10.0.26100.32230 — fixed in 10.0.26100.32230

How to fix

Upgrade to a fixed version: Microsoft Windows 10 1607 10.0.14393.8783; Microsoft Windows 10 10.0.17763.8276; Microsoft Windows 10 10.0.19044.6809; Microsoft Windows 10 10.0.19045.6809; Microsoft Windows 11 10.0.22631.6491; Microsoft Windows 11 10.0.26100.7623; Microsoft Windows 11 25H2 10.0.26200.7623; Microsoft Windows Server 2016 10.0.14393.8783; Microsoft Windows Server 2019 10.0.17763.8276; Microsoft Windows Server 2022 10.0.20348.4648; Microsoft Windows Server 2022, 23H2 Edition (Server Core installation) 10.0.25398.2092; Microsoft Windows Server 2025 10.0.26100.32230. Check the vendor advisory for mitigations.

References

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