CVE-2026-20816
Published: 13 January 2026
Summary
CVE-2026-20816 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 7.0th 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 CM-11 (User-installed Software) and SI-2 (Flaw Remediation).
Threat & Defense at a Glance
Threat & Defense Details
Mitigating Controls (NIST 800-53 r5)AI
Directly remediates the TOCTOU race condition in Windows Installer by requiring timely application of vendor patches as specified in the MSRC advisory.
Prohibits or strictly controls user-installed software via Windows Installer, preventing local low-privilege attackers from triggering the vulnerable installation process.
Enforces least privilege for local accounts, limiting the attack surface and impact of potential privilege escalation from the race condition exploitation.
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Direct local privilege escalation via exploitation of a TOCTOU race condition vulnerability in Windows Installer.
NVD Description
Time-of-check time-of-use (toctou) race condition in Windows Installer allows an authorized attacker to elevate privileges locally.
Deeper analysisAI
CVE-2026-20816 is a time-of-check time-of-use (TOCTOU) race condition vulnerability in Windows Installer, affecting Windows operating systems. Classified under CWE-367, it enables local privilege escalation for authorized attackers. The vulnerability received 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), indicating high severity due to its potential for significant impact on confidentiality, integrity, and availability with low complexity and privileges required.
An attacker with local access and low-level privileges (PR:L) can exploit this race condition in Windows Installer to elevate their privileges. By racing the time-of-check against time-of-use mechanism, the attacker can manipulate the installation process, potentially gaining higher privileges on the system and achieving high-impact outcomes across confidentiality, integrity, and availability.
The Microsoft Security Response Center advisory at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20816 provides details on mitigation, including available patches and recommended actions for affected Windows systems. Security practitioners should consult this reference for specific update guidance to address the vulnerability.
Details
- CWE(s)