CVE-2026-20921
Published: 13 January 2026
Summary
CVE-2026-20921 is a high-severity Race Condition (CWE-362) vulnerability in Microsoft Windows Server 2008. Its CVSS base score is 7.5 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked at the 15.9th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 SC-4 (Information in Shared System Resources) and SI-2 (Flaw Remediation).
Deeper analysis
CVE-2026-20921 is a race condition vulnerability (CWE-362) stemming from concurrent execution using a shared resource with improper synchronization in the Windows SMB Server. Published on January 13, 2026, it has a CVSS v3.1 base score of 7.5 (AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H), indicating high impact potential despite elevated attack complexity.
An authorized attacker with low privileges (PR:L) can exploit this vulnerability over the network (AV:N) without user interaction (UI:N). Successful exploitation enables privilege escalation, granting high levels of confidentiality, integrity, and availability impact (C:H/I:H/A:H) within the affected system.
Microsoft's update guide at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20921 provides details on mitigations and patches for this vulnerability.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-2122
Vulnerability details
Concurrent execution using shared resource with improper synchronization ('race condition') in Windows SMB Server allows an authorized attacker to elevate privileges over a network.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Race condition in Windows SMB Server directly enables remote exploitation for local privilege escalation (CWE-362) by low-privileged network attackers.
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
SI-2 requires timely identification, reporting, and correction of system flaws such as this race condition vulnerability via patching.
SC-4 prevents unauthorized and unintended information transfer via shared system resources, directly mitigating race conditions from improper synchronization.
AC-6 enforces least privilege, limiting the potential impact and scope of privilege escalation resulting from successful exploitation.