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Windows Credential Guard: Spoofing due to missing authentication

CVE-2026-70580High 7.8

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Summary

A critical function in Windows Credential Guard lacks authentication, so a local attacker can perform spoofing. The attacker needs a valid low-privilege account on the system, and no user interaction is required. Microsoft scores the impact as high for confidentiality, integrity and availability, with changed scope, and gives a base score of 8.8 (the CVE record shows 7.8). The flaw is not internet-facing, but it matters after a compromise, for example for lateral movement.

Affected

  • Windows 10 Version 1809 and Windows Server 2019 (including Server Core): 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 23H2: builds below 10.0.22631.7652
  • Windows 11 24H2: builds below 10.0.26100.9711
  • Windows 11 25H2: builds below 10.0.26200.9711
  • Windows 11 26H1: builds below 10.0.28000.3231
  • Windows 11 26H2: builds below 10.0.26300.9711
  • Windows Server 2022: builds below 10.0.20348.5761
  • Windows Server 2025 (including Server Core): builds below 10.0.26100.33650

Fixed in

  • Windows 10 1809 and Windows Server 2019: build 10.0.17763.9376 or later, expected in the October 2026 cumulative update
  • Update KB5126651 is mentioned by third parties but is not confirmed by the MSRC page. Verify it before rollout.
  • Windows 10 22H2: the fixed build is not confirmed, because one listing shows the 21H2 value. Check the MSRC advisory.

Workaround

Unknown. No vendor workaround or mitigation was found. Apply the patch.

Exploitation

  • Microsoft states the vulnerability is not publicly disclosed and not known to be exploited.
  • SSVC data in the NVD record: exploitation none, automatable no.
  • No public proof of concept and no CISA KEV entry were found. This is based on limited searches.

Our recommendation

  • Install the October 2026 cumulative update on affected systems after verifying the fixed build on the MSRC advisory.
  • Prioritise servers and admin workstations where Credential Guard is enabled.
  • Check whether systems still on Windows 10 1809 are supported (LTSC or Server 2019 lifecycle).
  • Review CVE-2026-70578, which affects the same component, in the same maintenance window.
  • Monitor authentication logs for unusual activity until patching is complete.

Information from Microsoft (Patch Tuesday October 2026)

Severity (Microsoft)
Important
Impact
Spoofing – Windows Credential Guard
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, 03:46.

Original description (NVD)

Missing authentication for critical function in Windows Credential Guard allows an authorized attacker to perform spoofing 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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