Microsoft has issued an urgent security update addressing CVE-2026-21511, a critical vulnerability affecting multiple Windows versions. Users must install patches immediately to prevent potential exploitation.
Microsoft has released a critical security update to address CVE-2026-21511, a vulnerability that could allow attackers to execute arbitrary code on affected systems. The flaw affects Windows 10 version 1809 and later, Windows Server 2019 and newer, and all supported versions of Windows 11.
The vulnerability exists in the Windows kernel and could be exploited when a user opens a specially crafted file or visits a malicious website. Microsoft rates this as a Critical severity issue with a CVSS score of 9.8 out of 10.
Affected Products and Versions
- Windows 10 version 1809 through 22H2
- Windows 11 version 21H2 and 22H2
- Windows Server 2019 and 2022
- Windows Server version 20H2 and later
Mitigation Steps
- Enable automatic updates or manually check for updates immediately
- Install the latest security patches released April 2026
- Verify installation by checking Windows Update history
- Restart systems after installation to complete the update process
Microsoft has not observed any active exploitation in the wild but urges immediate action due to the severity of the vulnerability. The company recommends organizations prioritize patching critical infrastructure and endpoints.
Additional security guidance and technical details are available through the Microsoft Security Response Center and the official Security Update Guide at msrc.microsoft.com/update-guide.
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