CVE-2026-58540 - Windows Installer Elevation of Privilege Vulnerability - is an improper authorization issue in Windows Installer that can allow elevation of privilege. The CVSS v3.1 base score is 7.8 (High) with a temporal score of 6.8. The vector is LOCAL, with LOW attack complexity, LOW privileges required, and no user interaction. Microsoft says exploitation is not publicly disclosed and has not been observed, with exploit code maturity UNPROVEN. Because this is a local-only elevation of privilege issue, enterprise risk is highest on systems where untrusted local code or users can run, rather than on network-exposed services.

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.
- Exploitation likelihood: Exploitation Less Likely; LOCAL vector, LOW attack complexity, LOW privileges required, and no user interaction.
- Severity for enterprise: High severity by CVSS, but lower exposure-driven risk than network-based issues because exploitation requires local access. Internal shared systems, endpoints, and environments that allow untrusted local execution are the main concern.
- Patch status: available; customer action is 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