CVE-2026-20921

7.5 highEPSS 1.2%

High (7.5) in microsoft. EPSS 1.2% chance of exploitation in the next 30 days.

Concurrent execution using shared resource with improper synchronization ('race condition') in Windows SMB Server allows an authorized attacker to elevate privileges over a network.

Severity

CVSS 3.1

7.5 high

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

EPSS: 1.2% chance of exploitation in the next 30 days; higher than 67% of CVEs (scores of 2026-10-31)
CWE: CWE-362
Published: 2026-01-13
Modified: 2026-07-30
Record from: the NVD, synced 2026-10-19

Affected

microsoft:windows_10_1607
microsoft:windows_10_1809
microsoft:windows_10_21h2
microsoft:windows_10_22h2
microsoft:windows_11_23h2
microsoft:windows_11_24h2
microsoft:windows_11_25h2
microsoft:windows_server_2008
microsoft:windows_server_2012
microsoft:windows_server_2016
microsoft:windows_server_2019
microsoft:windows_server_2022
microsoft:windows_server_2022_23h2
microsoft:windows_server_2025

References

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