Microsoft Windows Kernel: Heap-based buffer overflow allows local privilege escalation
Summary
A heap-based buffer overflow in the Windows Kernel affects several Windows 10, Windows 11 and Windows Server releases. An authorized local attacker with low privileges can elevate their privileges. The attack is not reachable directly from the internet and requires an existing foothold on the system, for example through phishing or a stolen credential.
Affected
- Windows 10 Version 1809 and Windows Server 2019 (including Server Core): builds from 10.0.17763.0 before 10.0.17763.9376
- Windows 10 Version 21H2: builds before 10.0.19044.7807
- Windows 10 Version 22H2: builds before 10.0.19045.7807
- Windows 11 Version 23H2: builds before 10.0.22631.7652
- Windows 11 Version 24H2: builds before 10.0.26100.9711
- Windows 11 Version 25H2: builds before 10.0.26200.9711
- Windows 11 Version 26H1: builds before 10.0.28000.3231
- Windows 11 Version 26H2: builds before 10.0.26300.9711
- Windows Server 2022: builds before 10.0.20348.5761
- Windows Server 2025 (including Server Core): builds before 10.0.26100.33650
Fixed in
- Windows 10 1809 and Server 2019: 10.0.17763.9376 (KB5126651, later KB5134124)
- Windows 10 21H2: 10.0.19044.7807
- Windows 10 22H2: 10.0.19045.7807
- Windows 11 23H2: 10.0.22631.7652
- 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 2022: 10.0.20348.5761
- Windows Server 2025: 10.0.26100.33650
No KB article explicitly listing this CVE was found; the build numbers come from the NVD and CNA data.
Workaround
Unknown. No vendor-documented workaround found. Patching is the required fix.
- Known issue with KB5126651: some on-premises Exchange servers had mail problems after the October 2026 update, and Microsoft documents a temporary registry workaround.
Exploitation
- Not known to be exploited in the wild.
- CISA SSVC assessment: exploitation none, not automatable, technical impact total.
- No public proof of concept found.
- EPSS about 0.0038 (low).
Our recommendation
- Install the newest cumulative update for your Windows branch on all affected systems, prioritising multi-user systems, terminal and file servers.
- Check Windows 10 1809 systems: they need ESU or LTSC to receive this fix.
- Before patching Exchange hosts, review the Microsoft known issues page for KB5126651.
- Limit local accounts and untrusted software on shared systems and monitor for privilege escalation.
- Verify version and patch details on the MSRC advisory, as it could not be retrieved during research.
Information from Microsoft (Patch Tuesday October 2026)
- Severity (Microsoft)
- Important
- Impact
- Elevation of privilege – Windows Kernel
- Status on Patch Tuesday
- Neither exploited nor publicly disclosed
- Exploitability assessment
- Exploitation unlikely
- 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 Response Center advisory msrc.microsoft.com
- NVD record mirror (Vulners) vulners.com
- CNA data (Vulners) vulners.com
- OpenCVE app.opencve.io
- Microsoft Update Catalog (KB5126651) www.catalog.update.microsoft.com
- Microsoft support, KB5134124 support.microsoft.com
- Microsoft known issues, Windows 10 1809 and Server 2019 learn.microsoft.com
- GitHub issue #91 (bug tracker entry) 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 2 Nov 2026, 02:43.
Original description (NVD)
Heap-based buffer overflow in Windows Kernel 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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