Improper link resolution before file access, known as "link following," exists in the Windows Container Isolation FS Filter Driver (unionfs.sys). An attacker with local or container‑level authority can exploit this flaw to tamper with files on the host, compromising data integrity. The weakness is a classic dereference of symbolic links before validating the target—CWE‑59. Because the vulnerability only allows manipulation of local files, the attack does not immediately expose sensitive data or enable remote code execution, but it can undermine system stability and trust.

The flaw affects Microsoft Windows 11 Version 24H2, 25H2, 26H2, and 26H1, as well as Microsoft Windows Server 2022 and Windows Server 2025, including their Server Core installations. These products rely on the unionfs.sys filter driver for container isolation, which is the component vulnerable.

The CVSS score of 5.5 indicates a moderate severity, and the EPSS score is unavailable. The vulnerability is not listed in CISA's KEV catalog. Attack requires an authorized local attacker with sufficient privileges to run a container or otherwise invoke unionfs.sys. If successful, an attacker can modify or delete files, potentially disabling system services or compromising the integrity of applications running in containers.