CVE-2026-20866
Published: 13 January 2026
Summary
CVE-2026-20866 is a high-severity Race Condition (CWE-362) vulnerability in Microsoft Windows 10 1809. Its CVSS base score is 7.8 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked at the 3.3th 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-2026-20866 is a race condition vulnerability (CWE-362) stemming from concurrent execution using a shared resource with improper synchronization in Windows Management Services. This flaw affects Windows systems and was published on 2026-01-13 with a CVSS v3.1 base score of 7.8 (AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H), rated as high severity due to its potential for significant impact across confidentiality, integrity, and availability.
An authorized local attacker with low privileges can exploit this vulnerability by racing to manipulate the shared resource in Windows Management Services, requiring high attack complexity but no user interaction. Successful exploitation enables privilege escalation, granting the attacker high-level access that could compromise the system through unauthorized data access, modification, or disruption.
The Microsoft Security Response Center advisory at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20866 provides details on mitigation, including available patches and recommended actions for affected Windows versions.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-2161
Vulnerability details
Concurrent execution using shared resource with improper synchronization ('race condition') in Windows Management Services allows an authorized attacker to elevate privileges locally.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Race condition in Windows Management Services directly enables local privilege escalation via exploitation of a shared resource flaw (T1068).
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Directly remediates the race condition vulnerability by applying vendor-provided patches for Windows Management Services.
Prevents unauthorized manipulation of shared system resources through concurrent access, countering the improper synchronization exploited in this race condition.
Enforces least privilege to restrict the potential impact and scope of successful local privilege escalation from low-privilege exploitation.