HIGH
Windows SMB Server Elevation of Privilege Vulnerability
Published Jan 13, 2026
7.5
HIGHCVSS 3.1
EPSS 1.19%
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.
Affected products
-
- Version 10.0.14393.0StatusaffectedConstraints<10.0.14393.8783
- Version
-
- Version 10.0.17763.0StatusaffectedConstraints<10.0.17763.8276
- Version
-
- Version 10.0.19044.0StatusaffectedConstraints<10.0.19044.6809
- Version
-
- Version 10.0.19045.0StatusaffectedConstraints<10.0.19045.6809
- Version
-
- Version 10.0.22631.0StatusaffectedConstraints<10.0.22631.6491
- Version
-
- Version 10.0.26100.0StatusaffectedConstraints<10.0.26100.7623
- Version
-
- Version 10.0.26200.0StatusaffectedConstraints<10.0.26200.7623
- Version
-
- Version 10.0.22631.0StatusaffectedConstraints<10.0.22631.6491
- Version
-
- Version 6.1.7601.0StatusaffectedConstraints<6.1.7601.28117
- Version
- Vendor Microsoft Product Windows Server 2008 R2 Service Pack 1 (Server Core installation) Defaultn/a
- Version 6.1.7601.0StatusaffectedConstraints<6.1.7601.28117
- Version
-
- Version 6.0.6003.0StatusaffectedConstraints<6.0.6003.23717
- Version
-
- Version 6.0.6003.0StatusaffectedConstraints<6.0.6003.23717
- Version
-
- Version 6.2.9200.0StatusaffectedConstraints<6.2.9200.25868
- Version
-
- Version 6.2.9200.0StatusaffectedConstraints<6.2.9200.25868
- Version
-
- Version 6.3.9600.0StatusaffectedConstraints<6.3.9600.22968
- Version
-
- Version 6.3.9600.0StatusaffectedConstraints<6.3.9600.22968
- Version
-
- Version 10.0.14393.0StatusaffectedConstraints<10.0.14393.8783
- Version
-
- Version 10.0.14393.0StatusaffectedConstraints<10.0.14393.8783
- Version
-
- Version 10.0.17763.0StatusaffectedConstraints<10.0.17763.8276
- Version
-
- Version 10.0.17763.0StatusaffectedConstraints<10.0.17763.8276
- Version
-
- Version 10.0.20348.0StatusaffectedConstraints<10.0.20348.4648
- Version
-
- Version 10.0.25398.0StatusaffectedConstraints<10.0.25398.2092
- Version
-
- Version 10.0.26100.0StatusaffectedConstraints<10.0.26100.32230
- Version
-
- Version 10.0.26100.0StatusaffectedConstraints<10.0.26100.32230
- Version
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Microsoft | Windows 10 Version 1607 | n/a |
| ||||||
| Microsoft | Windows 10 Version 1809 | n/a |
| ||||||
| Microsoft | Windows 10 Version 21H2 | n/a |
| ||||||
| Microsoft | Windows 10 Version 22H2 | n/a |
| ||||||
| Microsoft | Windows 11 Version 23H2 | n/a |
| ||||||
| Microsoft | Windows 11 Version 24H2 | n/a |
| ||||||
| Microsoft | Windows 11 Version 25H2 | n/a |
| ||||||
| Microsoft | Windows 11 version 23H2 | n/a |
| ||||||
| Microsoft | Windows Server 2008 R2 Service Pack 1 | n/a |
| ||||||
| Microsoft | Windows Server 2008 R2 Service Pack 1 (Server Core installation) | n/a |
| ||||||
| Microsoft | Windows Server 2008 Service Pack 2 | n/a |
| ||||||
| Microsoft | Windows Server 2008 Service Pack 2 (Server Core installation) | n/a |
| ||||||
| Microsoft | Windows Server 2012 | n/a |
| ||||||
| Microsoft | Windows Server 2012 (Server Core installation) | n/a |
| ||||||
| Microsoft | Windows Server 2012 R2 | n/a |
| ||||||
| Microsoft | Windows Server 2012 R2 (Server Core installation) | n/a |
| ||||||
| Microsoft | Windows Server 2016 | n/a |
| ||||||
| Microsoft | Windows Server 2016 (Server Core installation) | n/a |
| ||||||
| Microsoft | Windows Server 2019 | n/a |
| ||||||
| Microsoft | Windows Server 2019 (Server Core installation) | n/a |
| ||||||
| Microsoft | Windows Server 2022 | n/a |
| ||||||
| Microsoft | Windows Server 2022, 23H2 Edition (Server Core installation) | n/a |
| ||||||
| Microsoft | Windows Server 2025 | n/a |
| ||||||
| Microsoft | Windows Server 2025 (Server Core installation) | n/a |
|
OR
- < 10.0.14393.8783
- < 10.0.14393.8783
- < 10.0.17763.8276
- < 10.0.17763.8276
- < 10.0.19044.6809
- < 10.0.19045.6809
- < 10.0.22631.6491
- < 10.0.26100.7623
- < 10.0.26200.7623
- n/a
- n/a
- r2
- n/a
- r2
- < 10.0.14393.8783
- < 10.0.17763.8276
- < 10.0.20348.4648
- < 10.0.25398.2092
- < 10.0.26100.32230
No data.
No Red Hat product state for this CVE.
No package ranges for this CVE.
Remediation
No remediation recorded yet.
Metrics
No CVSS v4.0 score for this CVE.
7.5 HIGH CVE.org
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C
Attack Vector Network
Attack Complexity High
Privileges Required Low
User Interaction None
Scope Unchanged
Confidentiality Impact High
Integrity Impact High
Availability Impact High
Exploit Maturity Unreported
1 other source (NVD) ▾
7.5 HIGH NVD
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
Attack Vector Network
Attack Complexity High
Privileges Required Low
User Interaction None
Scope Unchanged
Confidentiality Impact High
Integrity Impact High
Availability Impact High
No CVSS v3.0 score for this CVE.
No CVSS v2.0 score for this CVE.
This CVE is not in the KEV list.
CISA SSVC (Vulnrichment)
Stakeholder-Specific Vulnerability Categorization from CISA ADP.
Exploitation
NoneAutomatable
NoTechnical Impact
TotalDecision
n/aAssessed Jan 14, 2026 · SSVC 2.0.3
1.19% 0.01193
Estimated probability of exploitation in the wild in the next 30 days (FIRST EPSS). As of Oct 1, 2026.
EPSS probability 0.01193
Score over time
Jan–Oct 2026- EPSS v4
- EPSS v5
Percentile over time
- EPSS v4
- EPSS v5
Table of values (3 key points)
Flat stretches are collapsed; showing up to 120 newest points.
| Date | Score | Percentile | Model |
|---|---|---|---|
| Oct 1, 2026 | 1.19% (0.01193) | 66.91th | v5 (v2026.06.15) |
| Jun 15, 2026 | 1.15% (0.01154) | 62.74th | v5 (v2026.06.15) |
| Jan 14, 2026 | 0.05% (0.00052) | 16.37th | v4 (v2025.03.14) |
Weaknesses (1)
References (3)
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20921 vendor-advisorypatchVendor 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
Change history (0)
No recorded changes yet.
Sources
CVE.org / MITRE
Status PUBLISHED
Assigner microsoft
Published Jan 13, 2026
Updated Jul 30, 2026
Reserved Dec 4, 2025
Link CVE-2026-20921
CISA Vulnrichment
Updated Jan 14, 2026