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Microsoft Windows VHD Miniport Driver: Heap overflow enables privilege escalation

CVE-2026-103555High 7.0

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Summary

A heap-based buffer overflow in the Virtual Hard Disk (VHD) Miniport Driver (vhdmp.sys) of Windows allows an authorized local user to elevate privileges to SYSTEM. The attacker needs local logon and low privileges, so the risk arises mainly after an initial foothold, for example through phishing or malware. Microsoft rates the issue Important with a CVSS 3.1 score of 7.0; no public exploit and no confirmed exploitation are known.

Affected

  • Windows 10 Version 1607 and Windows Server 2016: below 10.0.14393.9612
  • Windows 10 Version 1809: below 10.0.17763.9376
  • Windows 10 Version 21H2: below 10.0.19044.7807
  • Windows 10 Version 22H2: below 10.0.19045.7807
  • Windows 11 Version 23H2: below 10.0.22631.7652
  • Windows 11 Version 24H2 and 25H2: below 10.0.26100.9711 and 10.0.26200.9711
  • Windows 11 Version 26H1: below 10.0.28000.3231
  • Windows 11 Version 26H2: below 10.0.26300.9711
  • Windows Server 2012 and 2012 R2: below 6.2.9200.26434 and 6.3.9600.23470
  • Server Core installations of the above Server 2012 versions are also affected

The vendor table is authoritative; check the MSRC page for the complete list.

Fixed in

  • Windows 11 Version 23H2: KB5126653 (build 22631.7652)
  • Windows Server 2025 / Windows 11 24H2 line: KB5126646 (build 26100.33650)
  • Windows Server 2022: KB5126655 (build 20348.5761)
  • Monthly rollups: KB5126835 and KB5126836
  • Windows 10 1607 / Server 2016 and 1809 / Server 2019: KB number unknown; check the MSRC page before deployment

Workaround

Unknown. No mitigation was found in the sources reviewed; check the MSRC mitigations section directly.

Exploitation

  • Microsoft marks exploit code maturity as unproven (E:U) and report confidence as confirmed (RC:C).
  • A GitHub issue from October 11, 2026 describes the same bug in vhdmp.sys but is not a public exploit.
  • No public proof of concept found.
  • Exploitation in the wild: not known from the sources reviewed. CISA SSVC assessment: exploitation none, automatable no.
  • KEV and EPSS status not verified.

Our recommendation

  • Install the October 2026 Windows updates on all affected systems, starting with servers, terminal servers, and shared multi-user endpoints.
  • Determine the correct KB for each Windows version on the MSRC page.
  • Limit local logon on systems that cannot be patched, such as end-of-service Windows 10 1607, and document the risk acceptance.
  • Check the CISA KEV catalog and monitor vendor advisories for signs of exploitation.

Information from Microsoft (Patch Tuesday October 2026)

Severity (Microsoft)
Important
Impact
Elevation of privilege – Virtual Hard Disk (VHD) Miniport Driver
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 4 Nov 2026, 09:47.

Original description (NVD)

Heap-based buffer overflow in Virtual Hard Disk (VHD) Miniport Driver 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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