CVE-2025-49721
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedHeap-based buffer overflow in Windows Fast FAT Driver allows an unauthorized attacker to elevate privileges locally.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceHeap-based buffer overflow in the Windows Fast FAT Driver allows a local attacker to corrupt heap memory and achieve privilege escalation from unprivileged user context to elevated system privileges. The vulnerability resides in kernel-mode driver code responsible for FAT filesystem operations.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data< 10.0.10240.21073< 10.0.14393.8246< 10.0.17763.7558< 10.0.19044.6093< 10.0.19045.6093< 10.0.22621.5624< 10.0.22631.5624< 10.0.26100.4652CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Local
- Complexity
- Low
- Privileges
- None
- User interaction
- Required
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Check Windows version against affected rangesOpen Command Prompt and run 'winver' or 'systeminfo | findstr /B /C:"OS Name" /C:"OS Version"'. Compare the displayed version to the affected version ranges: Windows 10 1507 < 10.0.10240.21073, Windows 10 1607 < 10.0.14393.8246, Windows 10 1809 < 10.0.17763.7558, Windows 10 21h2 < 10.0.19044.6093, Windows 10 22h2 < 10.0.19045.6093, Windows 11 22h2 < 10.0.22621.5624, Windows 11 23h2 < 10.0.22631.5624, Windows 11 24h2 < 10.0.26100.4652Affected if The installed Windows version matches one of the affected versions and is lower than the patched version listed
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Check fastfat.sys driver file versionOpen Command Prompt and run 'dir C:\Windows\System32\drivers\fastfat.sys' or right-click the file in File Explorer, select Properties, and view the Details tab to see the File Version. Compare this version to the patched builds for your Windows release.Affected if The fastfat.sys file version is lower than the version corresponding to the patched build for your Windows release
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Check for loaded Fast FAT DriverOpen Command Prompt and run 'driverquery /v | findstr fastfat' or use PowerShell 'Get-Process | Where-Object {$_.ProcessName -like "*fastfat*"}' (though kernel drivers may not show in user processes). Alternatively, check loaded drivers with 'sc query fastfat'Affected if The fastfat driver is loaded or loaded at boot time (driver state shows RUNNING) on an affected Windows version
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Check for FAT filesystem volumesOpen Command Prompt and run 'mountvol' or 'wmic logicaldisk get name,filesystem' to list mounted volumes and their filesystem types. Also check 'fsutil fsinfo volumeinfo <drive letter>' for each drive.Affected if The system has any FAT-formatted volumes (FAT12, FAT16, FAT32, or exFAT) mounted, as these trigger the Fast FAT Driver to load
You are affected if your Windows version matches one of the affected builds AND the fastfat.sys version has not been updated to the patched version, particularly if the system uses FAT volumes.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scoped10.0.10240.2107310.0.14393.824610.0.17763.7558
Apply Microsoft security updates for Windows to patch the Fast FAT Driver vulnerability. Prioritize affected endpoints and verify successful patch deployment via vulnerability management or Windows Update.
Windows Security Update (Cumulative Update containing fix for CVE-2025-49721)
- Open Windows Settings and navigate to Update & Security > Windows Update
- Click 'Check for updates' to ensure you have the latest security patches
- Install any available updates, particularly cumulative security updates for your Windows version
- If automatic updates are disabled, enable them or manually download updates from the Microsoft Update Catalog
- After installation, restart the system to apply the kernel driver updates
- Verify the installed Windows version meets or exceeds the fixed version for your release: Windows 10 1507 >= 10.0.10240.21073, Windows 10 1607 >= 10.0.14393.8246, Windows 10 1809 >= 10.0.17763.7558, Windows 10 21h2 >= 10.0.19044.6093, Windows 10 22h2 >= 10.0.19045.6093, Windows 11 22h2 >= 10.0.22621.5624, Windows 11 23h2 >= 10.0.22631.5624, Windows 11 24h2 >= 10.0.26100.4652
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation6.0 h
- Implementation12.0 h
- Testing8.0 h
- Review / QA4.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2025-49721 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2025-49721 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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