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Debian LinuxOperating system · Debian

CVE-2021-39261

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_compressed_pwrite 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 the ntfs_compressed_pwrite function of NTFS-3G versions prior to 2021.8.22. The flaw is triggered when mounting a specially crafted malicious NTFS image, allowing potential 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. Verify NTFS-3G is installed
    Run 'ntfs-3g --version' or check your package manager (dpkg -l | grep ntfs-3g, rpm -qa | grep ntfs, or apt list --installed 2>/dev/null | grep ntfs)
    Affected if NTFS-3G package is not installed means the system does not use this component
  2. Determine installed NTFS-3G version
    Execute 'ntfs-3g --version' and note the output version number, or use 'dpkg -l ntfs-3g' on Debian-based systems
    Affected if Version is displayed as less than 2021.8.22 or the version string contains a date earlier than August 22, 2021
  3. Check Debian distribution version
    Run 'cat /etc/debian-version' or 'lsb_release -a' to identify your Debian release
    Affected if Running Debian 9, 10, or 11 and NTFS-3G is installed from the distribution's repositories (these ship vulnerable versions)
  4. Identify NTFS-3G package source
    Run 'apt-cache policy ntfs-3g' on Debian/Ubuntu to see the installed version and repository origin, or check /usr/bin/ntfs-3g file properties
    Affected if NTFS-3G originates from the distribution vendor rather than a current upstream build compiled after August 2021

A system is affected if NTFS-3G is installed with a version earlier than 2021.8.22, particularly on Debian 9/10/11 where the vendor ships vulnerable versions.

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 version 2021.8.22 or later (or Debian package ntfs-3g_1:2021.8.22-1 or later)

  1. 1. Update your system's package repository metadata: sudo apt-get update
  2. 2. Upgrade the ntfs-3g package to the fixed version: sudo apt-get install --only-upgrade ntfs-3g
  3. 3. Verify the installed version is 2021.8.22 or later: ntfs-3g --version
  4. 4. If the system has NTFS volumes mounted, unmount and remount them to ensure the patched library is in use
Caveat Minimal risk; NTFS-3G is a stable utility and this is a bugfix release. However, always test with critical data before production deployment.

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
  • Testing4.0 h
  • Review / QA2.0 h
10.0 hours of engineering $1,720
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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-2021-39261 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