Windows: Heap-based buffer overflow in Container Isolation FS Filter Driver

Summary

A heap-based buffer overflow (CWE-122) in the Windows Container Isolation FS Filter Driver (unionfs.sys) allows an authorized local attacker to elevate privileges. The attacker needs a local, low-privilege account and no user interaction is required. Remote attacks over the network are not described by the vendor.

Affected

• Windows 11 Version 23H2: 10.0.22631.0 to below 10.0.22631.7652
• Windows 11 Version 24H2: 10.0.26100.0 to below 10.0.26100.9711
• Windows 11 Version 25H2: 10.0.26200.0 to below 10.0.26200.9711
• Windows 11 Version 26H1: 10.0.28000.0 to below 10.0.28000.3231
• Windows 11 Version 26H2: 10.0.26300.0 to below 10.0.26300.9711
• Windows Server 2022: 10.0.20348.0 to below 10.0.20348.5761
• Windows Server 2025 (including Server Core): 10.0.26100.0 to below 10.0.26100.33650

Fixed in

• Install the Microsoft security update released on October 13, 2026 for the affected branch, then restart the system.
• Fixed builds: 10.0.22631.7652 or later (23H2), 10.0.26100.9711 or later (24H2), 10.0.26200.9711 or later (25H2), 10.0.28000.3231 or later (26H1), 10.0.26300.9711 or later (26H2), 10.0.20348.5761 or later (Server 2022), 10.0.26100.33650 or later (Server 2025).
• KB number: Unknown (see the MSRC update guide).

Workaround

Unknown. No workaround or mitigation is documented in the sources reviewed.

Exploitation

• MSRC does not report public exploit code; the sources reviewed describe the exploit status as not exploited.
• CISA SSVC: exploitation none, not automatable, total technical impact.
• Not listed in the CISA KEV catalog; EPSS below 1%.

Our recommendation

• Apply the October 2026 security update to all listed Windows 11 and Windows Server systems, prioritizing shared workstations, terminal servers and hosts running Windows containers.
• Verify the affected builds in the MSRC update guide before rollout, as the version list was taken from the CNA record.
• Restrict local logon and limit local accounts on multi-user systems.
• Monitor for unusual privilege changes and new local services on exposed hosts.

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-2026-97794 msrc.microsoft.com
• CVE record mirror (Vulners CVELIST) vulners.com
• OpenCVE: CVE-2026-97794 app.opencve.io
• Strix AI: CVE-2026-97794 www.strix.ai

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.