Microsoft Windows Win32k: Use-after-free allows local privilege escalation
Summary
A use-after-free vulnerability in the ICOMP component of the Win32k kernel-mode subsystem in Windows allows an authorized local attacker to elevate privileges. Exploitation requires local code execution or a logged-in account with low privileges, and the attack complexity is high. According to the CVSS vector, successful exploitation can fully compromise confidentiality, integrity and availability of the system.
Affected
- Windows 11 Version 24H2 (10.0.26100.0 to before 10.0.26100.9711 per CNA data)
- 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 installation (10.0.26100.0 to before 10.0.26100.33650)
Fixed in
- Install the October 2026 Windows cumulative update for the affected branch.
- Windows 11 24H2: fixed build per CNA data is 10.0.26100.9711. An OpenCVE record lists 10.0.26100.33650 for the same range, which conflicts with this value. Unresolved; verify the exact fixed build in the MSRC table.
- KB number for Windows 11 24H2: Unknown.
Workaround
Unknown. No vendor workaround is documented in the sources reviewed. Patching is the remedy.
Exploitation
- CISA SSVC: Exploitation none, Automatable no, Technical Impact total.
- EPSS approximately 0.003 (very low).
- No public proof of concept or exploit found for this CVE.
- Not confirmed in the CISA KEV catalogue; KEV was not queried directly.
- A Tenable plugin for the Server 2025 October 2026 update reports an exploit flag, but it is a bundle-level flag and could not be linked to this CVE.
Our recommendation
- Patch Windows 11 and Windows Server 2025 systems in the October 2026 update cycle, with priority for servers, terminal servers and shared multi-user workstations.
- Verify the exact fixed build for 24H2 in the MSRC advisory, because sources conflict.
- Keep endpoint protection active and enforce least-privilege accounts as compensating controls until patched.
- Monitor for unusual privilege changes or suspicious local processes on affected systems.
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 (CVE-2026-83566) msrc.microsoft.com
- OpenCVE CVE-2026-83566 app.opencve.io
- Vulners NVD mirror CVE-2026-83566 vulners.com
- Vulners CNA data mirror CVE-2026-83566 vulners.com
- Strix CVE-2026-83566 www.strix.ai
- Tenable plugin 365473 (bundle-level exploit flag) www.tenable.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, 08:44.
Original description (NVD)
Use after free in Windows Win32K - ICOMP 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.