CVE-2026-57091 is a Windows File History Service stack-based buffer overflow that can be used for elevation of privilege to SYSTEM. Microsoft rates it CVSS v3.1 base 7.8 and temporal 6.8, with a LOCAL attack vector, LOW attack complexity, LOW privileges required, and no user interaction. The issue has not been publicly disclosed or exploited according to the source data, but Microsoft marks exploitation as more likely. Because it is local-only, it is lower risk for internet-facing exposure than network-reachable flaws, but it remains important on systems where untrusted local access is possible.

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 More Likely; LOCAL vector with LOW attack complexity, LOW privileges required, and no user interaction.
- Severity for enterprise: High severity per CVSS, but enterprise exposure is mainly from local attackers rather than remote network attack paths. Risk is higher on shared systems, endpoints with untrusted local users, or environments where code execution has already been gained.
- 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 2016
- Windows Server 2019
- Windows Server 2022
- Windows Server 2025