CVE-2026-20921

  1. OpenCVE
  2. Vulnerabilities (CVE)
  3. CVE-2026-20921
Concurrent execution using shared resource with improper synchronization ('race condition') in Windows SMB Server allows an authorized attacker to elevate privileges over a network.

7.5 /10

CVSS v3 : HIGH

V3 Legend

Vector :

Exploitability : 1.6 / Impact : 5.9

Attack Vector NETWORK

Attack Complexity HIGH

Privileges Required LOW

User Interaction NONE

Confidentiality Impact HIGH

Integrity Impact HIGH

Availability Impact HIGH

Scope UNCHANGED

References
Link Resource
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
Configurations

Configuration 1 (hide)

OR cpe:2.3:o:microsoft:windows_10_1607:*:*:*:*:*:*:x64:*
cpe:2.3:o:microsoft:windows_10_1607:*:*:*:*:*:*:x86:*
cpe:2.3:o:microsoft:windows_10_1809:*:*:*:*:*:*:x64:*
cpe:2.3:o:microsoft:windows_10_1809:*:*:*:*:*:*:x86:*
cpe:2.3:o:microsoft:windows_10_21h2:*:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_10_22h2:*:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_11_23h2:*:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_11_24h2:*:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_11_25h2:*:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_server_2008:-:sp2:*:*:*:*:x64:*
cpe:2.3:o:microsoft:windows_server_2008:-:sp2:*:*:*:*:x86:*
cpe:2.3:o:microsoft:windows_server_2008:r2:sp1:*:*:*:*:x64:*
cpe:2.3:o:microsoft:windows_server_2012:-:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_server_2012:r2:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_server_2016:*:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_server_2019:*:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_server_2022:*:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_server_2022_23h2:*:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_server_2025:*:*:*:*:*:*:*:*
History

26 May 2026, 19:16

Type Values Removed Values Added
References
  • () 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 -
Summary
  • (es) Ejecución concurrente utilizando un recurso compartido con sincronización inadecuada ('condición de carrera') en el servidor SMB de Windows permite a un atacante autorizado elevar privilegios a través de una red.

15 Jan 2026, 21:15

Type Values Removed Values Added
CPE cpe:2.3:o:microsoft:windows_11_23h2:*:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_server_2008:-:sp2:*:*:*:*:x86:*
cpe:2.3:o:microsoft:windows_11_25h2:*:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_10_1607:*:*:*:*:*:*:x64:*
cpe:2.3:o:microsoft:windows_server_2012:r2:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_server_2008:r2:sp1:*:*:*:*:x64:*
cpe:2.3:o:microsoft:windows_10_1809:*:*:*:*:*:*:x86:*
cpe:2.3:o:microsoft:windows_server_2008:-:sp2:*:*:*:*:x64:*
cpe:2.3:o:microsoft:windows_10_1607:*:*:*:*:*:*:x86:*
cpe:2.3:o:microsoft:windows_server_2025:*:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_server_2012:-:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_11_24h2:*:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_10_22h2:*:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_server_2016:*:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_server_2019:*:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_10_1809:*:*:*:*:*:*:x64:*
cpe:2.3:o:microsoft:windows_server_2022_23h2:*:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_10_21h2:*:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_server_2022:*:*:*:*:*:*:*:*
First Time Microsoft windows 11 24h2
Microsoft windows 11 25h2
Microsoft windows Server 2022
Microsoft
Microsoft windows Server 2016
Microsoft windows 10 1607
Microsoft windows Server 2012
Microsoft windows Server 2008
Microsoft windows Server 2022 23h2
Microsoft windows 10 1809
Microsoft windows 10 21h2
Microsoft windows 11 23h2
Microsoft windows 10 22h2
Microsoft windows Server 2019
Microsoft windows Server 2025
References () https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20921 - () https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20921 - Vendor Advisory

13 Jan 2026, 18:16

Type Values Removed Values Added
New CVE
Information

Published : 2026-01-13 18:16

Updated : 2026-05-26 19:16

NVD link : CVE-2026-20921

Mitre link : CVE-2026-20921

CVE.ORG link : CVE-2026-20921

JSON object : View

Products Affected

microsoft

  • windows_11_25h2
  • windows_10_1607
  • windows_11_24h2
  • windows_10_1809
  • windows_11_23h2
  • windows_server_2012
  • windows_10_22h2
  • windows_server_2016
  • windows_server_2022_23h2
  • windows_server_2008
  • windows_10_21h2
  • windows_server_2022
  • windows_server_2019
  • windows_server_2025
CWE
CWE-362

Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')