Windows Installer: Heap-based buffer overflow allows local privilege escalation

Summary

Windows Installer, the Windows component for installing, repairing and removing MSI packages, contains a heap-based buffer overflow. An attacker with a low-privileged local account and no user interaction can exploit it to gain SYSTEM privileges on affected Windows 10, Windows 11 and Windows Server systems. The flaw is not reachable from the internet, but it is relevant wherever staff have local sessions or shared PCs are used.

Affected

• Windows 10 Version 1607 and Windows Server 2016 (including Server Core): before 10.0.14393.9688
• Windows 10 Version 1809 and Windows Server 2019 (including Server Core): before 10.0.17763.9487
• Windows 10 Version 21H2: before 10.0.19044.7846
• Windows 10 Version 22H2: before 10.0.19045.7846
• Windows 11 Version 23H2: before 10.0.22631.7711
• Windows 11 Version 24H2: before 10.0.26100.9974
• Windows 11 Version 25H2: before 10.0.26200.9974
• Windows 11 Version 26H1: before 10.0.28000.3501
• Windows 11 Version 26H2: before 10.0.26300.9974
• Windows Server 2022: before 10.0.20348.5870

Fixed in

Install the Microsoft security update for your branch. Fixed builds according to the CVE record:

• Windows 10 1607 / Server 2016: 10.0.14393.9688
• Windows 10 1809 / Server 2019: 10.0.17763.9487
• Windows 10 21H2: 10.0.19044.7846
• Windows 10 22H2: 10.0.19045.7846
• Windows 11 23H2: 10.0.22631.7711
• Windows 11 24H2: 10.0.26100.9974
• Windows 11 25H2 and 26H2: 10.0.26200.9974 and 10.0.26300.9974
• Windows 11 26H1: 10.0.28000.3501
• Windows Server 2022: 10.0.20348.5870

Verify the KB numbers on the MSRC advisory.

Workaround

Unknown. No workaround is documented by the vendor. Interim hardening from general practice (not from the advisory): restrict local administrator rights and who can install MSI packages, and monitor for unexpected privilege changes.

Exploitation

• Exploited in the wild: unknown. CISA SSVC lists exploitation as none.
• Public proof of concept: none found.
• Automatable: no.
• CVSS 3.1 base score 7.8 (High), vector AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H.

Our recommendation

• Install the Microsoft security update on all affected Windows 10, Windows 11 and Windows Server systems in the next regular patch cycle, starting with shared PCs, remote-access systems and machines of staff with local admin rights.
• Check the MSRC advisory for the exact fixed builds before rollout, and confirm that Windows 10 1607 and 1809 still receive updates.
• Limit local administrator rights and restrict MSI installation to IT staff.
• Monitor endpoints for unexpected privilege changes.

Public exploits iAttack code is publicly available (PoC on GitHub, Metasploit or Exploit-DB).

PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.

Research sources

• CVE.org record CVE-2026-96085 www.cve.org
• Microsoft Security Update Guide CVE-2026-96085 msrc.microsoft.com
• Strix CVE-2026-96085 (third-party mirror, verify builds) www.strix.ai
• PT-2026-112485 (unconfirmed relation to this CVE) 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 11 Nov 2026, 02:36.