Windows Installer: Local privilege escalation via integer underflow
Summary
An integer underflow in Windows Installer, the Windows component that installs, maintains and removes software packages, allows a locally authorized attacker to elevate privileges. The attacker needs a local account with low privileges and a high-complexity condition must be met. Microsoft has published fixes for the affected Windows 10, Windows 11 and Windows Server versions. CISA SSVC assessed exploitation as none, and no public proof of concept was found.
Affected
- Windows 10 Version 21H2: builds 10.0.19044.0 to below 10.0.19044.7807
- Windows 10 Version 22H2: builds 10.0.19045.0 to below 10.0.19045.7807
- Windows 11 Version 23H2: builds 10.0.22631.0 to below 10.0.22631.7652
- Windows 11 Version 24H2, 25H2, 26H2: builds 10.0.26100.0 / 10.0.26200.0 / 10.0.26300.0 to below 9711 of the respective build
- Windows 11 Version 26H1: builds 10.0.28000.0 to below 10.0.28000.3231
- Windows Server 2022: builds 10.0.20348.0 to below 10.0.20348.5761
- Windows Server 2025 (including Server Core): builds 10.0.26100.0 to below 10.0.26100.33650
Fixed in
- Windows 10 21H2: 10.0.19044.7807
- Windows 10 22H2: 10.0.19045.7807
- Windows 11 23H2: 10.0.22631.7652
- Windows 11 24H2 / 25H2 / 26H2: see MSRC for the exact build
- Windows 11 26H1: 10.0.28000.3231
- Windows Server 2022: 10.0.20348.5761
- Windows Server 2025: 10.0.26100.33650
- KB number: Unknown. The Microsoft security update table could not be verified; check MSRC or the Microsoft Update Catalog.
Workaround
- None documented. Applying the Microsoft security update is the fix.
- Hardening option only, not verified for this CVE: AppLocker or Windows Defender Exploit Guard can restrict or require signing for installers.
Exploitation
- CISA KEV: not listed.
- CISA SSVC: exploitation none, automatable no, technical impact total.
- Public proof of concept: none found.
- Unknown whether exploitation has been observed in the wild.
Our recommendation
- Patch affected systems with the Microsoft security update for CVE-2026-83676 as part of the normal monthly cycle; prioritize shared or multi-user systems.
- Windows 10 21H2 is out of general support; verify ESU enrollment before assuming a standard update covers it.
- Check whether any Windows 10 21H2 systems are still in use without ESU.
- Limit local accounts to least privilege and monitor for unexpected installer activity.
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)
- KB5126655, KB5126657, KB5126646, KB5127648, KB5126653, KB5127646
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Microsoft Security Update Guide: CVE-2026-83676 msrc.microsoft.com
- NVD record mirror (Vulners) vulners.com
- CVE List record mirror (Vulners) vulners.com
- OpenCVE entry app.opencve.io
- Tenable plugin for October 2026 Windows update www.tenable.com
- Positive Technologies PT-2026-112481 vulners.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 4 Nov 2026, 08:38.
Original description (NVD)
Integer underflow (wrap or wraparound) 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.
Affected? We can help.
We check whether your systems are affected, install updates and close the gap – continuously with the System Health Checker if you wish.