Windows Container Isolation CVE-2026-62775

Exploitation requires a local authenticated account with at least low privileges (PR:L per CVSS) on a Windows 11 26H1 system where the Windows Container Isolation FS Filter Driver (unionfs.sys) is loaded and active. The Container Isolation feature must be installed - it is present on systems running Windows containers via Docker, Windows Sandbox, or similar runtimes, but is not universally active on all Windows 11 deployments. Remote exploitation is not possible (AV:L). No user interaction is required once local access is established. Limiting factors include: requirement for a valid local session or container process execution context; systems without the Container Isolation feature loaded are not affected; the unchanged scope (S:U) means the attacker cannot directly pivot to other networked systems through this flaw alone.

Real-world risk is moderate and context-dependent. The CVSS base score of 5.5 reflects genuine high confidentiality impact (C:H) but is tempered by local-only attack vector (AV:L) and low privilege requirement (PR:L) - meaning network-based mass exploitation is impossible. SSVC rates the technical impact as partial and automatable as no, consistent with a scenario requiring deliberate per-target interaction. No CISA KEV listing and no public exploit code further reduce urgency. The AC:L (low complexity) metric indicates exploitation is straightforward once local access is obtained, which is a meaningful concern in shared container hosting environments or multi-tenant Windows systems. The S:U scope prevents this from being a direct pivot vehicle. Overall, this is a real information disclosure risk for organizations running Windows 11 26H1 with container workloads, but not a crisis-tier vulnerability - treat as a standard patch-cycle item unless sensitive data is processed in containerized workloads, in which case prioritize accordingly.

A low-privileged local user or container process on a Windows 11 26H1 host issues crafted filesystem requests to unionfs.sys, triggering the incorrect authorization path in the FS filter driver. The driver grants access to filesystem objects outside the caller's authorized container namespace due to the CWE-863 flaw, allowing the attacker to read sensitive files - potentially including host-level data or data from peer container instances. No public exploit code has been identified at time of analysis, so exploitation currently requires independent vulnerability research.