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Windows MDM: TOCTOU race condition allows local privilege escalation

CVE-2026-108396High 7.0

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Summary

A time-of-check time-of-use (TOCTOU) race condition in the Windows Modern Device Management (MDM) component allows an authorized local user to elevate privileges. The affected range covers supported Windows 10, Windows 11 and Windows Server builds, including Windows 10 version 1809 and Windows Server 2019. An attacker needs a local, low-privileged account and must win a timing race, which is hard to exploit reliably. A successful attack would give full control over confidentiality, integrity and availability of the system.

Affected

  • Windows 10 Version 1809 and Windows Server 2019 (including Server Core): builds 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

  • Fixed by the Microsoft October 2026 security updates for the builds listed above.
  • Windows 10 1809 / Server 2019: build 17763.9376 (reported as KB5126651, not yet verified against the MSRC advisory).
  • Verify the exact KB numbers for each build in the MSRC advisory before rollout.

Workaround

Unknown. No Microsoft-recommended interim mitigation was found in the sources.

Exploitation

  • Not known to be exploited in the wild; CISA SSVC lists exploitation as none and automatable as no.
  • No public proof of concept was found.
  • Not listed in CISA KEV at the time of research.

Our recommendation

  • Install the October 2026 cumulative update on all affected Windows and Server systems, starting with Windows 10 1809 and Server 2019 hosts.
  • Prioritise MDM-enrolled devices, shared PCs and terminal servers, where standard users can run code.
  • Check whether Windows 10 1809 hosts (LTSC/IoT) are still in use and verify their support status on Microsoft's lifecycle pages.
  • Monitor for a public proof of concept or KEV listing and reassess if one appears.

Information from Microsoft (Patch Tuesday October 2026)

Severity (Microsoft)
Important
Impact
Elevation of privilege – Windows Modern Device Management (MDM)
Status on Patch Tuesday
Neither exploited nor publicly disclosed
Exploitability assessment
Exploitation less likely
Product family
Windows, Windows ESU (Extended Security Updates)
Updates (KB)
KB5126651, KB5126657, KB5126655, KB5126653, KB5127648, KB5126646

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 4 Nov 2026, 09:43.

Original description (NVD)

Time-of-check time-of-use (toctou) race condition in Windows Modern Device Management (MDM) 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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