CVE-2021-39255

Out-of-bounds read via invalid NTFS attribute

Published Sep 7, 2021 · Updated Dec 2, 2025

Out-of-bounds read in NTFS-3G before 2021.8.22 allows local users to trigger an invalid memory read via a crafted NTFS image. The ntfs_attr_find_in_attrdef function processes an invalid filesystem attribute without enforcing the bounds required for safe access. Reaching the flaw requires NTFS-3G to process attacker-controlled filesystem metadata; public sources do not establish whether this specific read discloses memory or only interrupts the process.

CVSS severity7.8
High
EPSS probability0.42%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Out-of-bounds read in NTFS-3G before 2021.8.22 allows local users to trigger an invalid memory read via a crafted NTFS image. The ntfs_attr_find_in_attrdef function processes an invalid filesystem attribute without enforcing the bounds required for safe access. Reaching the flaw requires NTFS-3G to process attacker-controlled filesystem metadata; public sources do not establish whether this specific read discloses memory or only interrupts the process.

The record

CVE
CVE-2021-39255
Published
Sep 7, 2021
Updated
Dec 2, 2025
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-20, CWE-125, T1200
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Sep 7, 2021CVE publishedPublication date reported by the CVE source.
  2. Dec 2, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.8NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-20Improper Input Validation
CWE-125Out-of-bounds Read
T1200Hardware Additions

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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