Microsoft Windows Win32 Kernel Subsystem: Local privilege escalation via out-of-bounds read
Summary
An out-of-bounds read in the Windows Win32 Kernel Subsystem allows an authorized local attacker to elevate privileges to SYSTEM. The attacker needs an existing local user account and the attack is rated as high complexity. Remote exploitation is not described in the advisory data. The official vector also shows a scope change, which Microsoft's details should be checked for.
Affected
- Windows 11 Version 23H2 before 10.0.22631.7652
- 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 2022 before 10.0.20348.5761
- Windows Server 2025 (including Server Core) before 10.0.26100.33650
- Build numbers taken from the CNA record; verify on the MSRC update guide.
Fixed in
- Security update from the October 2026 cumulative updates, per the CVE record builds listed above.
- Reported patch names (unverified): KB5126653 (Windows 11 23H2), KB5126646 (Server 2025). Confirm on the MSRC page.
Workaround
Unknown. The CVE record provides no workaround; install the Microsoft security update.
Exploitation
- CISA SSVC: exploitation none, automatable no, technical impact total.
- No evidence found of exploitation in the wild or of a public proof of concept in the research; the CISA KEV catalogue was not checked directly.
Our recommendation
- Inventory Windows 11 and Windows Server systems and check their builds against the fixed versions.
- Install the October 2026 cumulative update, prioritising multi-user PCs, shared workstations and terminal servers.
- Limit local accounts and review access on terminal servers.
- Monitor for unusual privilege escalation events until patching is complete.
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-2026-85858 msrc.microsoft.com
- OpenCVE: CVE-2026-85858 app.opencve.io
- Vulners MSCVE: MS:CVE-2026-85858 vulners.com
- Vulners NVD: CVE-2026-85858 vulners.com
- Strix: CVE-2026-85858 www.strix.ai
- VulDB: 419336 vuldb.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, 01:55.
Original description (NVD)
Out-of-bounds read 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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