Microsoft Fixes Windows Shell, UI Core, and File Explorer Privilege Escalation Flaws

Microsoft published security updates for multiple Windows elevation-of-privilege vulnerabilities affecting Windows Shell, Windows User Interface Core, and Windows File Explorer, including CVE-2026-27918, CVE-2026-27911, CVE-2025-64661, and CVE-2025-64658. The issues could allow attackers to gain higher privileges on a vulnerable system after obtaining local access, extending a pattern of privilege-escalation risk across core Windows components.

Microsoft provided the most detail for CVE-2026-27911, which it rated Important with a CVSS 3.1 score of 7.8. The flaw stems from a race condition and use-after-free weakness in Windows User Interface Core and can be exploited by a low-privileged local attacker without user interaction. Successful exploitation could let an attacker escape a contained environment such as an AppContainer, raising privileges from Low Integrity Level to Medium Integrity Level. Microsoft said exploitation requires winning a race condition, assessed exploitation as unlikely at publication, and reported that the vulnerability had neither been publicly disclosed nor exploited before fixes were released.