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 16.3th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
Threat & Defense at a Glance
Threat & Defense Details
Likely Mitigating ControlsAI
Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.
Accurate timestamps from internal clocks enable detection of race conditions by providing reliable event ordering in audit logs.
Coordination of concurrent security activities reduces the probability that shared resources will be accessed simultaneously without proper synchronization.
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.
NVD 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.
Deeper analysisAI
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.
Details
- CWE(s)