Microsoft Windows Installer: Elevation of privilege via race condition
Summary
A race condition (CWE-362) and a use-after-free weakness (CWE-416) in Windows Installer allow a local attacker with a standard account to elevate privileges. The attack requires high complexity and a local account, and the attacker gains full control of the host if successful. Exposure is mainly on multi-user servers, terminal servers and workstations with local user accounts.
Affected
- Windows 10 Version 1607 and Windows Server 2016: builds before 10.0.14393.9612
- Windows 10 Version 1809: 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 and Version 26H2: builds before 10.0.26200.9711 and 10.0.26300.9711
- Windows 11 Version 26H1: builds before 10.0.28000.3231
- Windows Server 2012 (including Server Core): builds before 6.2.9200.26434
- Windows Server 2012 R2 (including Server Core): builds before 6.3.9600.23470
Fixed in
Installation of the cumulative Windows update for November 2026 (Patch Tuesday, 10 November 2026) or later, which provides the fixed builds listed under affected. Verify the exact builds and KB numbers in the MSRC advisory.
Workaround
Unknown.
Exploitation
- Not known to be exploited in the wild.
- No public proof of concept or exploit code found.
- CISA SSVC: exploitation none, not automatable, total technical impact.
- Rapid7 rates exploitation as less likely.
Our recommendation
- Install the November 2026 cumulative update on all affected Windows systems, prioritising multi-user servers, terminal servers and workstations with local accounts.
- Limit local logon rights and standard-user rights on servers and shared workstations.
- Monitor for unexpected MSI installations and privilege changes.
- Verify the fixed builds in the MSRC advisory before rollout.
Information from Microsoft (Patch Tuesday November 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)
- KB5126835, KB5126836, KB5126868, KB5126651, KB5126657, KB5126655
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Microsoft Security Update Guide: CVE-2026-119865 msrc.microsoft.com
- CVE Record CVE-2026-119865 www.cve.org
- Rapid7: Patch Tuesday November 2026 www.rapid7.com
- ZDI: October 2026 Security Update Review www.zerodayinitiative.com
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 11 Nov 2026, 08:36.
Original description (NVD)
Concurrent execution using shared resource with improper synchronization ('race condition') 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:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
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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