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Windows Kerberos: Integer underflow allows local privilege escalation

CVE-2026-70064High 7.8

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Summary

An integer underflow in the Windows Kerberos authentication component allows an attacker with a low-privilege local account to elevate privileges, potentially up to SYSTEM or domain-level control. The affected versions include Windows 10 1607, 1809, 21H2, 22H2, Windows 11 and Windows Server 2012 to 2016. The attack requires local access and no user interaction, and the vulnerability is not directly reachable from the internet.

Affected

  • Windows 10 Version 1607: builds below 10.0.14393.9612
  • Windows 10 Version 1809: 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 and 25H2, 26H2: builds below 10.0.26100.9711, 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 2016: builds below 10.0.14393.9612

Fixed in

  • Install the Microsoft security update of October 13, 2026 for the affected builds listed above.
  • Windows 10 Version 1607: build 10.0.14393.9612 or later.
  • The KB number for Windows 10 Version 1607 is unknown. Take it from the MSRC Security Update Guide.

Workaround

Unknown. No documented workaround was found. Installing the security update is the fix.

Exploitation

  • Not exploited in the wild according to the sources.
  • Not publicly disclosed, and no public exploit code is known.
  • Microsoft exploitability assessment: Exploitation Less Likely.
  • CISA SSVC: Exploitation none, Automatable no, Technical Impact total.
  • Not listed in the CISA KEV catalog.

Our recommendation

  • Inventory all Windows hosts and their exact builds, not only Windows 10 1607.
  • Install the October 2026 security update on every affected system.
  • Replace any Windows 10 1607 system that cannot be patched. Check the Microsoft Lifecycle page for the end of support of this version.
  • Restrict local logons on servers, terminal servers and shared machines, and limit who holds low-privilege accounts.
  • Monitor for unusual privilege changes and new administrative accounts on Active Directory member systems.

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 less likely
Product family
Windows, Windows ESU (Extended Security Updates)
Updates (KB)
KB5127648, KB5126651, KB5126655, KB5126657, KB5126646, KB5126653

Entry in the Microsoft Security Update Guide

Public exploits

PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.

Research sources

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, 04:26.

Original description (NVD)

Integer underflow (wrap or wraparound) 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:

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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