Is CVE-2026-20816 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-20816 being exploited in the wild.

How severe is CVE-2026-20816?

High severity, with a CVSS score of 7.8, published 13 January 2026.

Which products and versions are affected?

Microsoft Windows 11 Version 22H3, 23H2, 24H2, 25H2; Microsoft Windows Server 2008 R2 Service Pack 1; Microsoft Windows 10 Version 1607, 1809, 21H2, 22H2.

Is there a fix for CVE-2026-20816?

No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

How is CVE-2026-20816 attacked?

It is attacked with local access, in an operating system.

Am I affected by CVE-2026-20816?

Check whether you run Microsoft Windows 11, Microsoft Windows Server 2008 R2 or Microsoft Windows 10 at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-20816: Microsoft Windows Installer privilege escalation via TOCTOU race condition

CVE-2026-20816 · Severity: high · CVSS 7.8 · Published 2026-01-13

A security vulnerability has been identified in the Windows Installer, the standard service used by Windows to install and maintain software. An attacker who already has basic access to a computer could exploit a timing flaw to gain full administrative control over the system. This could allow them to view sensitive data, delete files, or install malicious software with high-level permissions.

Technologies: Microsoft Windows 11, Microsoft Windows Server 2008 R2, Microsoft Windows 10. Vendors: Microsoft.

Quick answers

Is CVE-2026-20816 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-20816 being exploited in the wild.
How severe is CVE-2026-20816?: High severity, with a CVSS score of 7.8, published 13 January 2026.
Which products and versions are affected?: Microsoft Windows 11 Version 22H3, 23H2, 24H2, 25H2; Microsoft Windows Server 2008 R2 Service Pack 1; Microsoft Windows 10 Version 1607, 1809, 21H2, 22H2.
Is there a fix for CVE-2026-20816?: No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2026-20816 attacked?: It is attacked with local access, in an operating system.
Am I affected by CVE-2026-20816?: Check whether you run Microsoft Windows 11, Microsoft Windows Server 2008 R2 or Microsoft Windows 10 at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

A race condition vulnerability (CWE-367) exists in the Windows Installer service. The flaw is a Time-of-Check Time-of-Use (TOCTOU) issue, where the service validates a file or resource but a window of opportunity exists for an attacker to replace that resource before it is actually used by the installer. An attacker with low-privileged local access can exploit this timing window to execute code with elevated system privileges. Microsoft has released security updates for various versions of Windows 10, Windows 11, and Windows Server to address this issue.

Affected products

Microsoft Windows 10 Version 1607, 1809, 21H2, 22H2
Microsoft Windows 11 Version 22H3, 23H2, 24H2, 25H2
Microsoft Windows Server 2008 R2 Service Pack 1

Timeline

2026-01-13: disclosed
2026-01-13: advisory

References

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20816

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