CVE-2026-50400 - Windows App Package Installer Elevation of Privilege Vulnerability - is a stack-based buffer overflow in Windows App Package Installer that can lead to elevation of privilege to SYSTEM. CVSS v3.1 base score is 7.8 (High) with a temporal score of 6.8; the attack vector is LOCAL, attack complexity is LOW, privileges required are LOW, and user interaction is NONE. Microsoft reports no public disclosure and no known exploitation, with exploit code maturity UNPROVEN and exploitation unlikely. Because this is a local privilege escalation issue, enterprise risk is highest on systems where an attacker can already run code or obtain local access.

Highlights:
- CVSS scores: Base 7.8 - Temporal 6.8
- Exploit status & code maturity: Publicly Disclosed: No; Exploited: No; Exploit Code Maturity: UNPROVEN.
- Impact: Elevation of Privilege; confidentiality, integrity, and availability impacts are all HIGH. Microsoft says a successful attacker could gain SYSTEM privileges.
- Exploitation likelihood: Exploitation Unlikely; vector is LOCAL with LOW attack complexity, LOW privileges required, and NO user interaction.
- Severity for enterprise: High severity in CVSS terms, but lower exposure than network-based issues because exploitation requires local access. Risk is most relevant on endpoints or servers where untrusted local code, users, or sessions are present.
- Patch status: available; customer action required.

Affected systems:
- Windows 10 1607
- Windows 10 1809
- Windows 10 21H2
- Windows 10 22H2
- Windows 11 24H2
- Windows 11 25H2
- Windows 11 26H1
- Windows 11 unspecified
- Windows Server 2012
- Windows Server 2012 R2
- Windows Server 2016
- Windows Server 2019
- Windows Server 2022
- Windows Server 2025