CVE-2025-21420: 
vulnerability analysis and mitigation

CVE-2025-21420 is a vulnerability in the Windows Disk Cleanup Tool (cleanmgr.exe) discovered and disclosed to Microsoft in February 2025. The vulnerability affects multiple versions of Windows operating systems including Windows 10, Windows 11, and Windows Server editions. This elevation of privilege vulnerability has been assigned a CVSS score of 7.8 (High) (NVD).

The vulnerability exists in the Windows Disk Cleanup Tool and involves a DLL sideloading technique that can be exploited through cleanmgr.exe. The flaw has a CVSS v3.1 base score of 7.8 with the following vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H, indicating local access, low attack complexity, low privileges required, and no user interaction needed (SecurityOnline).

If successfully exploited, the vulnerability allows an attacker to gain SYSTEM privileges on a vulnerable system, potentially leading to complete system compromise. The high CVSS impact scores for confidentiality, integrity, and availability (all rated as High) indicate the severe potential consequences of exploitation (SecurityOnline).

Microsoft has addressed this vulnerability in its February 2025 Patch Tuesday release. Users are strongly advised to apply the security update immediately to protect their systems. The patch is part of a larger update that addresses 55 security flaws, including four zero-day vulnerabilities (SecurityOnline).