Microsoft Windows Win32k: Use-after-free leads to local privilege escalation
Summary
A use-after-free flaw in the Win32k kernel subsystem of Windows 11 and Windows Server 2025 allows an authorized local user to elevate privileges. The attacker needs local access and a valid logon, and the attack is rated as complex. The flaw is not directly reachable from the internet; it matters once an attacker already has a foothold, for example through phishing or malware.
Affected
- 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 2025 (including Server Core): 10.0.26100.0 to before 10.0.26100.33650
- Windows 10 and older builds: Unknown.
Fixed in
- Windows 11 24H2: 10.0.26100.9711
- Windows 11 25H2: 10.0.26200.9711
- Windows 11 26H1: 10.0.28000.3231
- Windows 11 26H2: 10.0.26300.9711
- Windows Server 2025 (including Server Core): 10.0.26100.33650
- Update packages reported by third-party databases (verify on MSRC): KB5127648 (24H2/25H2/26H2), KB5127646 (26H1), KB5126646 (Server 2025).
Workaround
Unknown. No workaround or mitigation is documented in the sources reviewed. Patching is the available remedy.
Exploitation
- No public proof of concept found.
- No evidence of exploitation in the wild found.
- CISA SSVC: Exploitation none, Automatable no, Technical Impact total.
- Not listed in CISA KEV.
- EPSS is low (about 0.3%).
Our recommendation
- Install the October 2026 Windows security update on all affected Windows 11 and Server 2025 systems, prioritizing multi-user systems such as RDS/terminal servers and shared workstations.
- Check your asset inventory for affected builds, including 24H2 and 25H2 clients.
- Verify the affected and fixed builds on the MSRC advisory before rollout.
- Limit local logons on servers and monitor for unusual privilege changes until patched.
Information from Microsoft (Patch Tuesday October 2026)
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- MSRC Security Update Guide msrc.microsoft.com
- MSRC Security Update Guide (en-US) msrc.microsoft.com
- Talos October 2026 Patch Tuesday summary blog.talosintelligence.com
- Vulners CVE record (CVE List) vulners.com
- Vulners Microsoft CVE record vulners.com
- Vulners Rapid7 record vulners.com
- OpenCVE CVE record app.opencve.io
- Strix CVE record 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 4 Nov 2026, 08:53.
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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