Windows Win32k: Local privilege escalation via use-after-free
Summary
A use-after-free flaw in the Win32k kernel subsystem of Windows allows a locally authorized attacker to elevate privileges. An attacker with a low-privilege account on an affected host could gain SYSTEM rights. Attack complexity is high, and no in-the-wild exploitation or public proof of concept has been found.
Affected
- Windows 10 Version 1607 (builds before 10.0.14393.9612)
- Further Windows 10, Windows 11 and Windows Server versions are listed in the CNA record; check the MSRC table for exact builds.
Fixed in
- Windows 10 Version 1607: build 10.0.14393.9612 or later, included in Microsoft's October 2026 security updates
- Knowledge Base number for 1607: Unknown.
Workaround
- No vendor workaround known. Apply the update.
- General mitigation: restrict local user rights to what is needed (least privilege).
Exploitation
- No evidence of in-the-wild exploitation found. CISA SSVC: exploitation none.
- No public proof of concept found. Microsoft exploit code maturity: Unproven.
- EPSS score very low (approx. 0.3%).
Our recommendation
- Install the October 2026 Windows security updates, prioritizing Windows 10 1607 hosts and multi-user systems such as terminal servers.
- Verify the fixed build numbers against the MSRC table.
- Check whether 1607 is still supported and plan an upgrade or isolation of unsupported hosts.
- Restrict local logon and administrative rights on shared systems.
Information from Microsoft (Patch Tuesday October 2026)
- Severity (Microsoft)
- Important
- Impact
- Elevation of privilege – Windows Win32 Kernel Subsystem
- Status on Patch Tuesday
- Neither exploited nor publicly disclosed
- Exploitability assessment
- Exploitation less likely
- Product family
- Windows, Windows ESU (Extended Security Updates)
- Updates (KB)
- KB5126651, KB5126655, KB5126657, KB5126646, KB5127648, KB5126653
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Microsoft Security Update Guide (MSRC) msrc.microsoft.com
- NVD record via Vulners vulners.com
- CNA version data via Vulners vulners.com
- OpenCVE app.opencve.io
- Qualys October 2026 Patch Tuesday review blog.qualys.com
- GitHub watchlist issue github.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 4 Nov 2026, 09:02.
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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