Windows Container Isolation FS Filter Driver: Local privilege escalation
Summary
An improper access control flaw in the Windows Container Isolation FS Filter Driver (unionfs.sys) affects several Windows 11 and Windows Server versions. An authenticated local user with low privileges can exploit it to gain higher privileges, potentially up to SYSTEM. Exploitation requires local access and no user interaction.
Affected
- Windows 11 version 23H2: 10.0.22631.0 to before 10.0.22631.7652
- Windows 11 version 24H2: 10.0.26100.0 to before 10.0.26100.9711
- Windows 11 version 25H2: 10.0.26200.0 to before 10.0.26200.9711
- Windows 11 version 26H1: 10.0.28000.0 to before 10.0.28000.3231
- Windows 11 version 26H2: 10.0.26300.0 to before 10.0.26300.9711
- Windows Server 2022: 10.0.20348.0 to before 10.0.20348.5761
- Windows Server 2025 (including Server Core): 10.0.26100.0 to before 10.0.26100.33650
Fixed in
- Windows 11 version 23H2: build 10.0.22631.7652 or later
- Windows 11 version 24H2: build 10.0.26100.9711 or later
- Windows 11 version 25H2: build 10.0.26200.9711 or later
- Windows 11 version 26H1: build 10.0.28000.3231 or later
- Windows 11 version 26H2: build 10.0.26300.9711 or later
- Windows Server 2022: build 10.0.20348.5761 or later
- Windows Server 2025: build 10.0.26100.33650 or later
(Builds taken from the CVE record; verify the update numbers on the MSRC page.)
Workaround
Unknown. No vendor workaround specific to this CVE has been identified.
Exploitation
- CISA SSVC: exploitation none, not automatable.
- No public proof of concept found.
- EPSS 0.00353 (very low).
- Exploitation in the wild for this CVE is not confirmed.
Our recommendation
- Install the October 2026 security update on all affected Windows 11 and Windows Server systems.
- Prioritise multi-user systems, terminal servers and hosts running containers or development workloads.
- Verify the patch level after installation.
- Plan the upgrade of Windows 11 23H2 Enterprise and Education systems to a supported release, as end of servicing is approaching.
Information from Microsoft (Patch Tuesday October 2026)
- Severity (Microsoft)
- Important
- Impact
- Elevation of privilege – Windows Container Isolation FS Filter Driver (unionfs.sys)
- Status on Patch Tuesday
- Neither exploited nor publicly disclosed
- Exploitability assessment
- Exploitation less likely
- Product family
- Windows
- Updates (KB)
- KB5126655, KB5127646, KB5126653, KB5127648, KB5126646
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Microsoft Security Update Guide: CVE-2026-102202 msrc.microsoft.com
- NVD record mirror (Vulners): CVE-2026-102202 vulners.com
- CVE CNA record mirror (Vulners): CVE-2026-102202 vulners.com
- Qualys Patch Tuesday review, October 2026 blog.qualys.com
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, 05:15.
Original description (NVD)
Improper access control in Windows Container Isolation FS Filter Driver (unionfs.sys) allows an authorized attacker to elevate privileges locally.
NVD references (1)
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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