Microsoft Windows 11: Use-after-free in Win32 kernel subsystem allows privilege escalation
Summary
A use-after-free vulnerability (CWE-416) in the Windows Win32 Kernel Subsystem allows an attacker with local access and low privileges to elevate privileges to SYSTEM. No user interaction is required. The flaw is not remotely exploitable, but it is a serious second stage after phishing, malware or a stolen low-privilege account, especially on shared or multi-user systems.
Affected
- Windows 11 Version 23H2 before 10.0.22631.7652 (x64 and arm64)
- Windows 11 Version 24H2 before 10.0.26100.9711
- Windows 11 Version 25H2 before 10.0.26200.9711
- Windows 11 Version 26H1 before 10.0.28000.3231
- Windows 11 Version 26H2 before 10.0.26300.9711
- Windows Server 2025 (including Server Core) before 10.0.26100.33650 (x64)
Fixed in
- Install the October 2026 cumulative update for each affected version (build numbers as listed in the affected section; verify on the MSRC Security Update Guide before rollout)
- Third-party trackers name KB5126653 (Windows 11 23H2) and KB5126646 (Windows Server 2025); confirm these on MSRC
Workaround
Unknown. No vendor-documented workaround has been identified. Apply the security update.
Exploitation
- Publicly disclosed: No (per MSRC data)
- Exploit code maturity: Unproven
- CISA SSVC: exploitation none, automatable no
- CISA KEV entry: not verified
- EPSS: low (about 0.0034)
Our recommendation
- Install the October 2026 security update on all affected Windows 11 and Windows Server 2025 systems, with priority on terminal servers, RDS hosts and shared workstations.
- Verify the exact fixed build numbers and KB articles on the MSRC Security Update Guide before deployment.
- Check that no KEV entry exists before concluding the flaw is not exploited.
- Review local accounts and limit low-privilege access on shared systems; monitor for unusual privilege changes and new SYSTEM processes.
Information from Microsoft (Patch Tuesday October 2026)
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Microsoft Security Update Guide: CVE-2026-85804 msrc.microsoft.com
- MSRC Security Update Guide (en-US): CVE-2026-85804 msrc.microsoft.com
- Vulners: NVD record CVE-2026-85804 vulners.com
- OpenCVE: CVE-2026-85804 app.opencve.io
- Talos: Microsoft Patch Tuesday for October 2026 blog.talosintelligence.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, 02:07.
Original description (NVD)
Use after free in Windows Win32 Kernel Subsystem 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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