OnlyFm252
Windows SMB Server

CVE-2026-20927 — Windows SMB Server Denial of Service Vulnerability

Important CVSS 5.3 EPSS 0.00892 2026-01 archive

Executive Summary

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

Overview

5.3
CVSS MEDIUM
Important
MS Severity
Not Exploited
MS Exploit Status
Exploitation Unlikely
MS Exploit Likelihood
Category Denial of Service
Released Jan 13 2026
Last Updated Jan 13 2026
Publicly Disclosed No
CISA KEV Not Listed
Known Exploits None Known
EPSS Score 0.00892 — 0.54703 percentile
NVD CVSS 5.3 MEDIUM — matches MSRC

CVSS Vector

CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H/E:U/RL:O/RC:C
ATTACK VECTOR
Network
ATTACK COMPLEXITY
High
PRIVILEGES REQUIRED
Low
USER INTERACTION
None
SCOPE
Unchanged
CONFIDENTIALITY
None
INTEGRITY
None
AVAILABILITY
High
EXPLOIT CODE MATURITY
Unproven
REMEDIATION LEVEL
Official Fix
REPORT CONFIDENCE
Confirmed
Temporal Score: 4.6

EPSS Score

0.00892
probability of exploitation in the next 30 days
0.54703 percentile - updated 2026-06-21
View on FIRST.org

Affected Products

29 affected products
Product KB Article Severity Impact Restart Required
Windows 10 Version 1607 for 32-bit Systems 5073722 (Security Update) Important Denial of Service Yes
Windows 10 Version 1607 for x64-based Systems 5073722 (Security Update) Important Denial of Service Yes
Windows 10 Version 1809 for 32-bit Systems 5073723 (Security Update) Important Denial of Service Yes
Windows 10 Version 1809 for x64-based Systems 5073723 (Security Update) Important Denial of Service Yes
Windows 10 Version 21H2 for 32-bit Systems 5073724 (Security Update) Important Denial of Service Yes
Windows 10 Version 21H2 for ARM64-based Systems 5073724 (Security Update) Important Denial of Service Yes
Windows 10 Version 21H2 for x64-based Systems 5073724 (Security Update) Important Denial of Service Yes
Windows 10 Version 22H2 for 32-bit Systems 5073724 (Security Update) Important Denial of Service Yes
Windows 10 Version 22H2 for ARM64-based Systems 5073724 (Security Update) Important Denial of Service Yes
Windows 10 Version 22H2 for x64-based Systems 5073724 (Security Update) Important Denial of Service Yes
Windows 11 Version 23H2 for ARM64-based Systems 5073455 (Security Update) Important Denial of Service Yes
Windows 11 Version 23H2 for x64-based Systems 5073455 (Security Update) Important Denial of Service Yes
Windows 11 Version 24H2 for ARM64-based Systems 5074109 (Security Update) Important Denial of Service Yes
Windows 11 Version 24H2 for x64-based Systems 5074109 (Security Update) Important Denial of Service Yes
Windows 11 Version 25H2 for ARM64-based Systems 5074109 (Security Update) Important Denial of Service Yes
Windows 11 Version 25H2 for x64-based Systems 5074109 (Security Update) Important Denial of Service Yes
Windows Server 2008 for 32-bit Systems Service Pack 2 5073697 (Monthly Rollup) 5073700 (Security Only) Important Denial of Service 5071504 Base: 5.3 Temporal: 4.6 Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H/E:U/RL:O/RC:C 6.0.6003.23717 Yes None Windows Server 2008 for 32-bit Systems Service Pack 2 (Server Core installation) 5073697 (Monthly Rollup) 5073700 (Security Only) Important Denial of Service 5071504 Base: 5.3 Temporal: 4.6 Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H/E:U/RL:O/RC:C 6.0.6003.23717 Yes None Windows Server 2008 for x64-based Systems Service Pack 2 5073697 (Monthly Rollup) 5073700 (Security Only) Important Denial of Service 5071504 Base: 5.3 Temporal: 4.6 Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H/E:U/RL:O/RC:C 6.0.6003.23717 Yes None Windows Server 2008 for x64-based Systems Service Pack 2 (Server Core installation) 5073697 (Monthly Rollup) 5073700 (Security Only) Important Denial of Service 5071504 Base: 5.3 Temporal: 4.6 Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H/E:U/RL:O/RC:C 6.0.6003.23717 Yes None Windows Server 2008 R2 for x64-based Systems Service Pack 1 5073695 (Monthly Rollup) 5073699 (Security Only) Important Denial of Service 5071501 Base: 5.3 Temporal: 4.6 Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H/E:U/RL:O/RC:C 6.1.7601.28117 Yes None Windows Server 2008 R2 for x64-based Systems Service Pack 1 (Server Core installation) 5073695 (Monthly Rollup) 5073699 (Security Only) Important Denial of Service 5071501 Base: 5.3 Temporal: 4.6 Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H/E:U/RL:O/RC:C 6.1.7601.28117 Yes None Windows Server 2012 5073698 (Monthly Rollup) Important Denial of Service Yes
Windows Server 2012 (Server Core installation) 5073698 (Monthly Rollup) Important Denial of Service Yes
Windows Server 2012 R2 5073696 (Monthly Rollup) Important Denial of Service Yes
Windows Server 2012 R2 (Server Core installation) 5073696 (Monthly Rollup) Important Denial of Service Yes
Windows Server 2016 5073722 (Security Update) Important Denial of Service Yes
Windows Server 2016 (Server Core installation) 5073722 (Security Update) Important Denial of Service Yes
Windows Server 2019 5073723 (Security Update) Important Denial of Service Yes
Windows Server 2019 (Server Core installation) 5073723 (Security Update) Important Denial of Service Yes
Windows Server 2022 5073457 (Security Update) Important Denial of Service Yes
Windows Server 2022 (Server Core installation) 5073457 (Security Update) Important Denial of Service Yes
Windows Server 2022, 23H2 Edition (Server Core installation) 5073450 (Security Update) Important Denial of Service Yes
Windows Server 2025 5073379 (Security Update) Important Denial of Service Yes
Windows Server 2025 (Server Core installation) 5073379 (Security Update) Important Denial of Service Yes

Patches

10 patches
Article Type Restart
5073722 Security Update Yes
5073723 Security Update Yes
5073724 Security Update Yes
5073455 Security Update Yes
5074109 Security Update Yes
5073698 Monthly Rollup Yes
5073696 Monthly Rollup Yes
5073457 Security Update Yes
5073450 Security Update Yes
5073379 Security Update Yes

Known Exploits

Acknowledgments

Microsoft

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