CVE-2026-20831
Published: 13 January 2026
Summary
CVE-2026-20831 is a high-severity Time-of-check Time-of-use (TOCTOU) Race Condition (CWE-367) vulnerability in Microsoft Windows Server 2008. 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 7.1th 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 SI-2 (Flaw Remediation) and AC-6 (Least Privilege).
Threat & Defense at a Glance
Threat & Defense Details
Mitigating Controls (NIST 800-53 r5)AI
Requires timely identification, reporting, and correction of system flaws like this TOCTOU race condition in the Windows Ancillary Function Driver for WinSock via vendor patches.
Enforces least privilege to restrict the scope and impact of local low-privilege attackers exploiting the privilege escalation vulnerability.
Enables continuous monitoring of systems to identify unauthorized privilege escalations from exploitation of the TOCTOU race condition.
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
TOCTOU race condition in kernel driver directly enables local privilege escalation via exploitation of a vulnerable system component.
NVD Description
Time-of-check time-of-use (toctou) race condition in Windows Ancillary Function Driver for WinSock allows an authorized attacker to elevate privileges locally.
Deeper analysisAI
CVE-2026-20831 is a time-of-check time-of-use (TOCTOU) race condition in the Windows Ancillary Function Driver for WinSock, affecting Windows systems. Published on 2026-01-13, this vulnerability is cataloged under CWE-367 and carries a CVSS v3.1 base score of 7.8 (AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H), reflecting high severity due to its potential for significant local impact.
A local attacker with low privileges (PR:L) can exploit this race condition without requiring user interaction or high complexity. Successful exploitation enables privilege escalation, granting the attacker high levels of control over confidentiality, integrity, and availability on the affected system.
The Microsoft Security Response Center advisory at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20831 provides details on mitigation, including available patches and recommended actions for remediation.
Details
- CWE(s)