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FreeBSDOperating system

CVE-2020-25579

MEDIUM · 5.3 CVSS v3.1 Published 2021-03-26
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
62/100
Remediation priority · Elevated
Remotely reachable No privileges Zero-click

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 · unedited
In FreeBSD 12.2-STABLE before r368969, 11.4-STABLE before r369047, 12.2-RELEASE before p3, 12.1-RELEASE before p13 and 11.4-RELEASE before p7 msdosfs(5) was failing to zero-fill a pair of padding fields in the dirent structure, resulting in a leak of three uninitialized bytes.

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 confidence

The msdosfs filesystem driver in FreeBSD fails to zero-fill padding fields in the dirent structure when reading directory entries from FAT filesystems, causing 3 bytes of uninitialized kernel stack/heap memory to leak into user-space.

MitigationUpdate FreeBSD to version 12.2-RELEASE p3, 12.1-RELEASE p13, 11.4-RELEASE p7 or later, or corresponding STABLE branches after r368969 (12.2) and r369047 (11.4).

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
FreeBSDOperating system
Affected:= 11.4= 12.1= 12.2

CVSS 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
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
None
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

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 checks

Work through these to decide whether this CVE applies to you.

  1. Identify FreeBSD version
    Run `freebsd-version` or `uname -r` to determine the installed FreeBSD release version
    Affected if The version matches 11.4, 12.1, or 12.2 specifically (not later patch levels)
  2. Verify msdosfs driver availability
    Check if the msdosfs kernel module is loaded: `kldstat | grep msdosfs` or attempt to mount a FAT filesystem to confirm driver presence
    Affected if The msdosfs driver is loaded or loadable on the system
  3. Detect mounted FAT filesystems
    Run `mount | grep msdosfs` or `df -t msdosfs` to list any currently mounted FAT-based filesystems
    Affected if Any FAT or FAT32 filesystems are mounted using the msdosfs driver
  4. Check for FAT filesystem access
    Inspect running processes or scripts that may access FAT-formatted media (USB drives, SD cards) via msdosfs, or use `fstat` to find open files on FAT mounts
    Affected if The system accesses or can access FAT filesystems through the msdosfs driver

A system is affected if it runs FreeBSD 11.4, 12.1, or 12.2 and uses the msdosfs driver to access FAT filesystems, as the uninitialized memory leak occurs when reading directory entries from those filesystems.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Update FreeBSD to version 12.2-RELEASE p3, 12.1-RELEASE p13, 11.4-RELEASE p7 or later, or corresponding STABLE branches after r368969 (12.2) and r369047 (11.4).

Fix this in FreeBSD Scoped from the published advisory
  • Consultation1.0 h
  • Implementation2.0 h
  • Testing3.0 h
  • Review / QA1.0 h
7.0 hours of engineering $1,190
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Scan for this in your stack

Free · runs locally
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2020-25579 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • 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
  • No spam, self-promotion, credentials, or personal data