CVE-2026-20921

CVE Database · CVE-2026-20921

CVE-2026-20921

· HIGHModified

CVSS v3.1

7.5

EPSS

1.15%

Published

Jan 13, 2026

Modified

May 26, 2026

Public PoC / Exploit (1)

All weaponized →

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Links to public security research (Exploit-DB, Nuclei, Trickest, GitHub) for defensive use only.

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.

CVSS Vector

CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H

Weaknesses (CWE)

CWE-362

Affected Products (19)

microsoft · windows_10_1607 (up to 10.0.14393.8783)vulnerable

microsoft · windows_10_1809 (up to 10.0.17763.8276)vulnerable

microsoft · windows_10_21h2 (up to 10.0.19044.6809)vulnerable

microsoft · windows_10_22h2 (up to 10.0.19045.6809)vulnerable

microsoft · windows_11_23h2 (up to 10.0.22631.6491)vulnerable

microsoft · windows_11_24h2 (up to 10.0.26100.7623)vulnerable

References (3)

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20921

Vendor Advisory

https://www.vicarius.io/vsociety/posts/cve-2026-20921-detection-script-race-condition-vulnerability-in-windows-smb-server

https://www.vicarius.io/vsociety/posts/cve-2026-20921-remediation-script-race-condition-vulnerability-in-windows-smb-server

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