Medium severity · published Jan 13, 2026
CVE-2026-20927
Windows SMB Server Denial of Service Vulnerability
5.3
CVSS
0.9%
EPSS
No
On KEV
Description
Concurrent execution using shared resource with improper synchronization ('race condition') in Windows SMB Server allows an authorized attacker to deny service over a network.
CVSS vector
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
High
Privileges
Low
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.9% · higher than 60% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
W1
Windows 10 Version 1607 · Microsoft
10.0.14393.0 before 10.0.14393.8783 · source: vendor
W1
Windows 10 Version 1809 · Microsoft
10.0.17763.0 before 10.0.17763.8276 · source: vendor
W1
Windows 10 Version 21H2 · Microsoft
10.0.19044.0 before 10.0.19044.6809 · source: vendor
W1
Windows 10 Version 22H2 · Microsoft
10.0.19045.0 before 10.0.19045.6809 · source: vendor
W1
Windows 11 Version 24H2 · Microsoft
10.0.26100.0 before 10.0.26100.7623 · source: vendor
W1
Windows 11 Version 25H2 · Microsoft
10.0.26200.0 before 10.0.26200.7623 · source: vendor
W1
Windows 11 version 23H2 · Microsoft
10.0.22631.0 before 10.0.22631.6491; 10.0.22631.0 before 10.0.22631.6491 · source: vendor
WS
Windows Server 2008 R2 Service Pack 1 · Microsoft
6.1.7601.0 before 6.1.7601.28117 · source: vendor
WS
Windows Server 2008 R2 Service Pack 1 (Server Core installation) · Microsoft
6.1.7601.0 before 6.1.7601.28117 · source: vendor
WS
Windows Server 2008 Service Pack 2 · Microsoft
6.0.6003.0 before 6.0.6003.23717 · source: vendor
WS
Windows Server 2008 Service Pack 2 (Server Core installation) · Microsoft
6.0.6003.0 before 6.0.6003.23717 · source: vendor
WS
Windows Server 2012 · Microsoft
6.2.9200.0 before 6.2.9200.25868 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-20927
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-20927
Vendor Advisory
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20927
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