Raw vector
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:HSummary
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 Path Interception (T1034); ranked at the 23th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to AC-25 (Reference Monitor) and AC-3 (Access Enforcement) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
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.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-2187
Vulnerability Data
Time-of-check time-of-use (toctou) race condition in Windows Ancillary Function Driver for WinSock allows an authorized attacker to elevate privileges locally.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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V15.4.2V17.2.6
Mitigating Controls (NIST 800-53 r5) AI
A reference monitor that is always invoked and analyzable structurally eliminates the non-atomic check-then-use pattern underlying TOCTOU.
Access enforcement that performs an atomic check-and-use decision directly stops the window in which a TOCTOU race can be exploited.
Process isolation limits the blast radius of a successful TOCTOU exploitation but does not remove the race itself.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Secure SDLC practices directly include coding standards and reviews that prevent TOCTOU race conditions.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Reliable, synchronized time across systems narrows the exploitable window in which a resource state can change between a security check and its use.