CVE-2025-24985

CVE-2025-24985 is an integer overflow (CWE-190) in the Windows Fast FAT file system driver that can lead to a buffer overflow condition (CWE-122) when the driver processes crafted FAT file system structures. Because the Fast FAT driver handles FAT-formatted storage, the flaw is triggered locally, most plausibly by mounting or interacting with a specially crafted FAT-formatted disk image or removable medium, with user interaction required per the CVSS vector. A successful exploit allows an unauthorized local attacker to execute code on the affected machine, with high impact to confidentiality, integrity, and availability (CVSS 3.1 base score 7.8, High). All Windows client versions from Windows 10 1507 through Windows 11 24H2 and Windows Server 2008/2012/2016/2019 are in the affected scope, meaning essentially any unpatched Windows system on those version lines is exposed. The flaw is being actively exploited: CISA added it to the Known Exploited Vulnerabilities catalog on 2025-03-11, Microsoft fixed it in the March 2025 Patch Tuesday release as one of six actively exploited zero-days, and EPSS currently estimates a 3.8% chance of exploitation in the next 30 days (89th percentile); ransomware use is listed as unknown.

What to do: Install Microsoft's March 2025 Windows cumulative security updates on every affected Windows 10, Windows 11, and Windows Server host, and prioritize endpoints that mount untrusted removable media or disk images; federal agencies must apply the fix within the CISA BOD 22-01 deadline tied to the 2025-03-11 KEV listing. Until systems are patched, discourage or restrict use of untrusted FAT-formatted media and crafted disk images, and inventory your estate for the affected version branches (Windows 10 1507/1607/1809/21H2/22H2, Windows 11 22H2/23H2/24H2, Server 2008/2012/2016/2019). Because ransomware use is listed as unknown, treat this as a high-priority patch given active exploitation is confirmed.