CVE-2025-62221

CVE-2025-62221 is a use-after-free flaw (CWE-416) in the Windows Cloud Files Mini Filter Driver, the in-box kernel component that handles cloud storage placeholder files. An attacker who already has low-privileged access on a local machine can trigger the flaw through operations involving the affected driver, with no user interaction required. Successful exploitation elevates the attacker's privileges on the local host, with high impact on confidentiality, integrity, and availability (CVSS 7.8), meaning effective full compromise of the machine. All listed Windows 10, Windows 11, and Windows Server builds are affected, and Microsoft shipped fixes in its December 2025 Patch Tuesday releases. The flaw was added to CISA's Known Exploited Vulnerabilities catalog on 2025-12-09, indicating exploitation in the wild; EPSS is 2.5% (84th percentile) and no public proof-of-concept is known.

What to do: Deploy Microsoft's December 2025 Patch Tuesday cumulative updates (released on or around 2025-12-09) for each affected Windows 10, Windows 11, and Windows Server build via Windows Update, WSUS, or Intune, and confirm the update installed before treating hosts as remediated. Prioritize this patch given active exploitation and KEV status (federal agencies must follow BOD 22-01 timelines or the vendor's mitigations); no standalone workaround or public PoC is documented. Because this is a local privilege escalation, roll out first to fleets where low-privileged users routinely execute code, such as workstations and terminal/RDS servers.