dbcve.org
Debian LinuxOperating system · Debian

CVE-2021-39256

HIGH · 7.8 CVSS v3.1 Published 2021-09-07
Fix available
A fix is available. Upgrade to 2021.8.22 or later.
See remediation →
80/100
Remediation priority · High
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
A crafted NTFS image can cause a heap-based buffer overflow in ntfs_inode_lookup_by_name in NTFS-3G < 2021.8.22.

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

A heap-based buffer overflow vulnerability exists in NTFS-3G's ntfs_inode_lookup_by_name function when parsing a specially crafted NTFS image. An attacker can trigger this by providing a malicious NTFS filesystem to a user or application that mounts it, potentially leading to code execution or denial of service.

MitigationUpdate NTFS-3G to version 2021.8.22 or later. Avoid mounting untrusted NTFS images from unknown sources until the update is applied.

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
Debian LinuxOperating system
Affected:= 9.0= 10.0= 11.0
Ntfs 3gApplication
Affected:< 2021.8.22

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
Local
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/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 checks

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

  1. Check if NTFS-3G is installed
    Run 'which ntfs-3g' or 'dpkg -l | grep ntfs-3g' on Debian-based systems to verify the ntfs-3g package is present
    Affected if NTFS-3G is not installed means the system does not use this vulnerable component, but if installed proceed to version check
  2. Identify the installed NTFS-3G version
    Run 'ntfs-3g --version' or 'dpkg -s ntfs-3g | grep Version' to obtain the exact version number
    Affected if Version is below 2021.8.22 (for Tuxera NTFS-3G) or the package version matches Debian 9.0, 10.0, or 11.0 repositories (which ship vulnerable versions)
  3. Check the Debian package source version
    Run 'apt-cache policy ntfs-3g' to see which version is currently installed and what versions are available in the repository
    Affected if The installed version is the one shipped with Debian 9, 10, or 11 (check the version number against Debian release package repositories)
  4. Verify if untrusted NTFS images are mounted
    Review system logs or mount history for 'mount -t ntfs' commands, and check if there are automated mounts of external or untrusted NTFS media
    Affected if The system mounts NTFS images from untrusted or unknown sources without verification, making exploitation possible if the NTFS-3G version is vulnerable

A system is affected if NTFS-3G is installed with a version prior to 2021.8.22 (or the Debian-shipped version matching Debian 9/10/11) AND the system mounts NTFS images from potentially untrusted sources.

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.

dbcve · scoped
Upgrade available Upgrade to 2021.8.22 or later
Fixed in 2021.8.22
Interim mitigation

Update NTFS-3G to version 2021.8.22 or later. Avoid mounting untrusted NTFS images from unknown sources until the update is applied.

Recommended fix High confidence

NTFS-3G 2021.8.22 or later

  1. Update the NTFS-3G package to version 2021.8.22 or later through your distribution's package manager
  2. For Debian systems: Run 'apt update && apt install ntfs-3g' to get the latest fixed version
  3. Verify the installed version with 'ntfs-3g --version' to confirm the update was successful

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Debian Linux Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing3.0 h
  • Review / QA1.0 h
8.0 hours of engineering $1,390
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Scan for this in your stack

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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-2021-39256 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