Windows 10 1809 Kernel: Heap-based buffer overflow enables privilege escalation
Summary
A heap-based buffer overflow in the Windows Kernel of Windows 10 version 1809 and Windows Server 2019 allows a local attacker to elevate privileges. The attacker needs an existing authorized, low-privilege account on the system. Successful exploitation can lead to full control of the system (SYSTEM rights).
Affected
- Windows 10 Version 1809: builds 10.0.17763.0 to below 10.0.17763.9376
- Windows Server 2019 (including Server Core): builds 10.0.17763.0 to below 10.0.17763.9376
Fixed in
- Windows 10 Version 1809 and Windows Server 2019: build 10.0.17763.9376 or higher, delivered by the October 2026 cumulative update KB5126651 (released 13 October 2026)
Workaround
Unknown. No vendor-documented workaround was found. Installing the update is the recommended fix.
Exploitation
- CISA SSVC: exploitation none, not automatable, total technical impact
- No public exploitation or proof of concept found in the reviewed sources
- EPSS score 0.00341; not verified against the CISA KEV catalog
Our recommendation
- Install KB5126651 or a later cumulative update on all Windows 10 1809 and Server 2019 systems
- Identify devices still running Windows 10 1809 and plan their replacement or upgrade, as the client edition is out of support
- Confirm the build number (17763.9376 or higher) in your asset inventory
- Prioritize multi-user terminal servers and shared PCs
- Verify the affected and fixed versions on the MSRC advisory before rollout
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
- MSRC Security Update Guide: CVE-2026-70121 msrc.microsoft.com
- Vulners NVD record: CVE-2026-70121 vulners.com
- Vulners CVE List record: CVE-2026-70121 vulners.com
- Vulners Microsoft CVE record: MS:CVE-2026-70121 vulners.com
- Microsoft Update Catalog: KB5126651 www.catalog.update.microsoft.com
- Microsoft Support: KB5126651 (Windows 10 1809) support.microsoft.com
- Theori public bug tracker entry for CVE-2026-70121 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, 04:08.
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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