CVE-2026-20934
Published: 13 January 2026
Summary
CVE-2026-20934 is a high-severity Race Condition (CWE-362) vulnerability in Microsoft Windows 10 21H2. 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 9.8th 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-2026-20934 is a race condition vulnerability (CWE-362) in the Windows SMB Server, stemming from concurrent execution using a shared resource with improper synchronization. Published on 2026-01-13, it carries 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 severity due to its potential for significant impact across confidentiality, integrity, and availability.
An authorized attacker with low privileges (PR:L) can exploit this vulnerability over the network (AV:N), though it requires high attack complexity (AC:H) and no user interaction (UI:N). Successful exploitation enables privilege escalation, allowing the attacker to achieve high-impact outcomes on the targeted system.
Mitigation details are available in the Microsoft Security Response Center advisory at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20934.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-2139
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 local privilege escalation via network exploitation of a remote service component.
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Directly mitigates the race condition by identifying, prioritizing, and applying vendor patches or updates for the specific vulnerability in Windows SMB Server.
Prevents unauthorized manipulation or transfer via shared system resources by enforcing proper isolation and synchronization mechanisms exploited in the SMB Server race condition.
Limits the impact of privilege escalation by ensuring low-privilege accounts have minimal access necessary to interact with the SMB Server over the network.