Windows: Elevation of privilege in Container Isolation FS Filter Driver

Summary

Improper access control in the Windows Container Isolation FS Filter Driver (unionfs.sys) allows an authorized local user to elevate privileges. An attacker needs a valid low-privileged account on the affected host and can then gain SYSTEM-level rights, with high impact on confidentiality, integrity and availability. The risk is mainly relevant on multi-user systems, terminal servers, developer machines and hosts running containers. Microsoft rates the issue as Important, with a CVSS 3.1 base score of 7.8 (High).

Affected

• Windows 11 version 23H2: builds 10.0.22631.0 before 10.0.22631.7652
• Windows 11 version 24H2: builds 10.0.26100.0 before 10.0.26100.9711 (per CVE record; verify on MSRC)
• Windows 11 version 25H2: builds 10.0.26200.0 before 10.0.26200.9711 (per CVE record; verify on MSRC)
• Windows 11 version 26H2: builds 10.0.26300.0 before 10.0.26300.9711 (per CVE record; verify on MSRC)
• Windows Server 2022: builds 10.0.20348.0 before 10.0.20348.5761
• Windows Server 2025 (including Server Core): builds 10.0.26100.0 before 10.0.26100.33650

Fixed in

• Windows 11 version 23H2: build 10.0.22631.7652 (KB5126653)
• Windows Server 2025 (including Server Core): build 10.0.26100.33650 (KB5126646)
• Windows Server 2022: build 10.0.20348.5761 (KB5126655)
• Windows 11 versions 24H2, 25H2 and 26H2: Unknown. Check the MSRC Security Update Guide for the exact fixed builds.

Workaround

Unknown. No vendor-published mitigation is known; applying the security update is the recommended fix.

Exploitation

• CISA SSVC: Exploitation none, Automatable no, Technical Impact total
• Not listed in CISA KEV; EPSS below 1%
• No public proof of concept or known in-the-wild exploitation at the time of research

Our recommendation

• Install the Windows security update for the affected build as part of the normal monthly cycle, and prioritize hosts with Docker or containers and multi-user access (terminal servers, developer machines).
• Verify that each host is on the fixed build for its Windows branch (23H2, 24H2, 25H2, 26H2, Server 2022, Server 2025).
• Restrict local logon rights and remove unneeded local accounts on shared systems.
• Check related IDs CVE-2026-102202, CVE-2026-97794 and CVE-2026-97787, which describe the same unionfs.sys issue, and confirm they are patched too.

Public exploits iAttack code is publicly available (PoC on GitHub, Metasploit or Exploit-DB).

PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.

Research sources

• MSRC Security Update Guide: CVE-2026-97792 msrc.microsoft.com
• Vulners CVE list entry: CVE-2026-97792 vulners.com
• OpenCVE: CVE-2026-97792 app.opencve.io
• Vulners NVD: CVE-2026-102202 (same unionfs.sys issue, KB5126653 build reference) vulners.com
• Vulners EUVD-2026-100357 (KB references for other branches) vulners.com
• OpenCVE: CVE-2026-97794 (component description) app.opencve.io

Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 2 Nov 2026, 00:27.