Improper access control in the Windows Container Isolation Filesystem Filter Driver (unionfs.sys) permits a local attacker with authorized access to bypass privilege checks and gain higher rights. The weakness, identified as CWE-59, involves improper restriction of operations within the bounds of a resource, leading to potential escalation of privileges on the host machine.

Microsoft Windows 11 versions 23H2, 24H2, 25H2, 26H2, and 26H1, as well as Windows Server 2022 and Windows Server 2025—including the Server Core installation—are affected by this vulnerability.

The vulnerability carries a CVSS score of 7.8, indicating a high potential impact. The EPSS score is not available, and the flaw is not listed in the CISA KEV catalog. Based on the description, it is inferred that the attack vector is local and requires an authorized user context. Once exploited, an attacker can elevate privileges within the container environment and potentially affect the host system.