Microsoft Windows Kerberos: Use-after-free leads to local privilege escalation
Summary
A use-after-free memory flaw in the Windows Kerberos implementation allows an authorized local user to elevate privileges. An attacker needs an existing low-privilege account and local access, so remote exploitation without prior access is not expected. The CNA record lists many Windows 10, 11 and Server builds, not only Windows 10 1607. Microsoft has published fixes in the October 2026 Patch Tuesday.
Affected
- Windows 10 Version 1607 and Windows Server 2016: builds below 10.0.14393.9612
- Windows 10 Version 1809 and Windows Server 2019: builds below 10.0.17763.9376
- Windows 10 Version 21H2: builds below 10.0.19044.7807
- Windows 10 Version 22H2: builds below 10.0.19045.7807
- Windows 11 Version 23H2: builds below 10.0.22631.7652
- Windows 11 Version 24H2: builds below 10.0.26100.9711
- Windows 11 Version 25H2 and 26H2: builds below 10.0.26200.9711 and 10.0.26300.9711
- Windows 11 Version 26H1: builds below 10.0.28000.3231
- Windows Server 2012 and 2012 R2 (including Server Core): builds below 6.2.9200.26434 and 6.3.9600.23470
- Windows Server 2022 and 2025: see MSRC for exact builds
Fixed in
- Microsoft has released fixes in the October 2026 security update for the affected builds listed above.
- Windows 10 1607 fixed build: 10.0.14393.9612 (per CNA range data).
- KB numbers for Windows 10 1607, 21H2 and 22H2: Unknown. Check the MSRC page.
Workaround
- Unknown. No vendor workaround was identified.
Exploitation
- No evidence of exploitation in the wild found.
- No public proof of concept found.
- CISA SSVC: Exploitation none, Automatable no, Technical Impact total.
- EPSS score is very low (about 0.003).
Our recommendation
- Install the October 2026 Windows security updates, prioritising servers, terminal servers, file servers and multi-user systems.
- Replace any Windows 10 1607 system; it is end-of-life and may receive no further fixes.
- Restrict local logon on shared systems and remove unneeded local accounts.
- Monitor for unusual privilege changes and failed or unexpected privileged activity.
- Re-check the MSRC page and CISA KEV for updates.
Information from Microsoft (Patch Tuesday October 2026)
- Severity (Microsoft)
- Important
- Impact
- Elevation of privilege – Windows Kerberos
- Status on Patch Tuesday
- Neither exploited nor publicly disclosed
- Exploitability assessment
- Exploitation more likely
- Product family
- Windows, Windows ESU (Extended Security Updates)
- Updates (KB)
- KB5127648, KB5126651, KB5126655, KB5126657, KB5126646, KB5126653
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Microsoft Security Update Guide: CVE-2026-70241 msrc.microsoft.com
- Vulners: CVE-2026-70241 CVE list record vulners.com
- Vulners: Microsoft advisory mirror (MS:CVE-2026-70241) vulners.com
- Rapid7 Vulners: Microsoft Windows CVE-2026-70241 vulners.com
- Qualys: Microsoft Patch Tuesday October 2026 review blog.qualys.com
- OpenCVE: CVE-2026-70241 (CISA SSVC data) app.opencve.io
- Strix: CVE-2026-70241 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, 09:00.
Original description (NVD)
Use after free in Windows Kerberos 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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