Microsoft Windows 11: Elevation of privilege in unionfs.sys filter driver
Summary
A type confusion flaw in the Windows Container Isolation FS Filter Driver (unionfs.sys) allows an authorized local attacker to elevate privileges. The attacker needs a valid local account and a foothold on the system, and the attack is complex. The CVE record lists only Windows 11 version 26H1. Microsoft has released a fix.
Affected
- Microsoft Windows 11 version 26H1, builds 10.0.28000.0 to before 10.0.28000.3501
Fixed in
- Microsoft Windows 11 version 26H1, build 10.0.28000.3501 or later
Workaround
Unknown. No vendor workaround is listed; applying the update is the remedy.
Exploitation
- CISA SSVC assessment: exploitation none, automatable no, technical impact total
- No public exploit or known exploitation found at the time of research
- Not listed in CISA KEV at the time of research
Our recommendation
- Inventory Windows 11 26H1 devices and record their build numbers
- Install the update that brings the build to 10.0.28000.3501 or later, after confirming the KB on the MSRC page
- Prioritise shared workstations, terminal servers and hosts running Windows containers
- Monitor for public exploits and KEV listing after patching
Information from Microsoft (Patch Tuesday November 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)
- KB5132059
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Microsoft Security Response Center: CVE-2026-112753 msrc.microsoft.com
- CVE Record CVE-2026-112753 www.cve.org
- Strix: CVE-2026-112753 www.strix.ai
- OSV: AZL-112753 osv.dev
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 11 Nov 2026, 09:27.
Original description (NVD)
Access of resource using incompatible type ('type confusion') 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.
Affected? We can help.
We check whether your systems are affected, install updates and close the gap – continuously with the System Health Checker if you wish.