CVE-2026-20871 is a use-after-free vulnerability (CWE-416) affecting the Desktop Windows Manager in Microsoft Windows 10 Version 21H2 (build 10.0.19044.0). This flaw enables an authorized local attacker to elevate privileges on the affected system. The vulnerability has been assigned a CVSS v3.1 base score of 7.8, indicating high severity, with attack vector local, low attack complexity, and requiring privileges but no user interaction. Microsoft has published an official fix for this vulnerability, as documented in their security update guide.

Successful exploitation of this vulnerability could allow an authorized local attacker to elevate their privileges, potentially gaining higher-level access to the system. This could lead to full system compromise depending on the privileges gained. The confidentiality, integrity, and availability impacts are all rated high according to the CVSS vector.

An official fix is available from Microsoft. It is recommended to apply the security update provided by Microsoft for Windows 10 Version 21H2 (build 10.0.19044.0) as soon as possible to remediate this vulnerability. Refer to the Microsoft security update guide at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20871 for detailed patch information and installation instructions.