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CVE Record

CVE-2021-39261: A crafted NTFS image can cause a heap-based buffer overflow in ntfs_compressed_pwrite in NTFS-3G < 2021.8.22.

A crafted NTFS image can cause a heap-based buffer overflow in ntfs_compressed_pwrite in NTFS-3G < 2021.8.22.

MediumCVSS 6.7Not KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

NTFS-3G before 2021.8.22 can mishandle a malicious NTFS filesystem image and corrupt heap memory. The issue requires local access with high privileges, so it is not internet-facing. It matters where privileged systems mount or write untrusted NTFS drives or images.

Executive priority

Treat as a targeted local exposure issue, not an emergency internet-wide risk. Prioritize patching systems that process untrusted NTFS media or images with privileged tools.

Technical view

The flaw is a heap-based buffer overflow in ntfs_compressed_pwrite, triggered by a crafted NTFS image. The CVSS vector is local, low complexity, high privileges required, no user interaction, with high confidentiality, integrity, and availability impact.

Likely exposure

Exposure is most likely on Linux or Unix systems using NTFS-3G older than 2021.8.22, especially systems that handle removable media, forensic images, backups, or user-supplied NTFS filesystem images.

Exploitation context

The provided sources do not show CISA KEV listing or active exploitation. Practical exploitation requires a crafted NTFS image and a privileged local context that causes vulnerable NTFS-3G write handling to process it.

Researcher notes

Evidence identifies NTFS-3G before 2021.8.22 and distribution updates, but the supplied affected-product metadata is incomplete. Avoid assuming exploit availability or affected downstream versions beyond cited advisories.

Mitigation direction

  • Upgrade NTFS-3G to 2021.8.22 or later where available.
  • Apply fixed distribution packages from Debian, Gentoo, or the relevant vendor.
  • Restrict privileged mounting or writing of untrusted NTFS images until patched.
  • Review workflows that process removable drives or externally supplied filesystem images.

Validation and detection

  • Inventory installed ntfs-3g versions across Linux and Unix systems.
  • Confirm packages are at upstream 2021.8.22 or a vendor-fixed backport.
  • Identify privileged services or operators that process NTFS images.
  • Check vendor advisories for platform-specific fixed package versions.
Prepared
Confidence
high
Sources
7

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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CVE-2021-39261 mapping review

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Vulnerability profileCVE Program record
Severity
Medium
CVSS
6.7 (3.1)
Known Exploited
No
Published

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

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

1CVSS vectors
0Timeline events
0ADP providers
6Source links

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
6.7CVSS 3.1MediumCVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H0.85.9Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

6.7Medium
CVSS 3.1 vector shape for CVE-2021-39261Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
n/an/an/aListed
Weakness

CWE details

CWE-20

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Improper Input Validation

Improper Input Validation represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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