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Microsoft Windows: Elevation of privilege in Windows Installer via stack overflow

CVE-2026-83767High 7.8

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Summary

A stack-based buffer overflow in Windows Installer, the Windows component that installs, repairs and removes software packages, allows an authorized local user to elevate privileges. The attacker needs a valid low-privileged account or code already running on the device. Microsoft rates the flaw CVSS 7.8 (High), and the CVE record lists no exploitation details.

Affected

  • Windows 10 Version 1607 (10.0.14393.0 before 10.0.14393.9612)
  • Windows 10 Version 1809 (10.0.17763.0 before 10.0.17763.9376)
  • Windows 10 Version 21H2 (10.0.19044.0 before 10.0.19044.7807)
  • Windows 10 Version 22H2 (10.0.19045.0 before 10.0.19045.7807)
  • Windows 11 Version 23H2 (10.0.22631.0 before 10.0.22631.7652)
  • Windows 11 Version 24H2 (10.0.26100.0 before 10.0.26100.9711)
  • Windows 11 Version 25H2 (10.0.26200.0 before 10.0.26200.9711)
  • Windows 11 Version 26H1 (10.0.28000.0 before 10.0.28000.3231)
  • Windows 11 Version 26H2 (10.0.26300.0 before 10.0.26300.9711)
  • Windows Server 2012 incl. Server Core (6.2.9200.0 before 6.2.9200.26434)
  • Windows Server 2012 R2 incl. Server Core (6.3.9600.0 before 6.3.9600.23470)
  • Windows Server 2016 (10.0.14393.0 before 10.0.14393.9612)
  • The NVD CPE lists only Windows 10 1607; the CNA data covers the entries above.

Fixed in

  • Install the Microsoft October 2026 security update for each affected build.
  • Fixed builds: see the list above; the Windows 10 22H2 fixed build in secondary sources is inconsistent and must be verified on the MSRC page.
  • The KB numbers for the affected builds are not confirmed in the available sources; check the MSRC advisory.

Workaround

Unknown. No vendor-confirmed workaround is available. Until patching is complete, restrict local logon to required users, remove unneeded local accounts, and verify that the 'AlwaysInstallElevated' policy is disabled.

Exploitation

  • Not listed in CISA KEV.
  • CISA SSVC: exploitation none, automatable no, technical impact total.
  • EPSS 0.0031 (low).
  • No public proof-of-concept found; absence of evidence is not proof.

Our recommendation

  • Inventory all Windows 10, Windows 11 and Windows Server systems, not only Windows 10 1607.
  • Prioritize multi-user, terminal and server systems and any device still on Windows 10 1607, which is out of support in its own right.
  • Apply the October 2026 Microsoft security update and verify the installed build number.
  • Keep third-party software that uses MSI installers up to date.
  • Monitor for suspicious installer activity and new privilege escalation reports.

Information from Microsoft (Patch Tuesday October 2026)

Severity (Microsoft)
Important
Impact
Elevation of privilege – Windows Installer
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, 03:05.

Original description (NVD)

Stack-based buffer overflow in Windows Installer 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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