CVE-2021-39261

Privileged code execution via compressed-write heap overflow

Published Sep 7, 2021 · Updated Dec 5, 2025

Heap-based buffer overflow in NTFS-3G before 2021.8.22 allows local users to execute privileged code via a crafted NTFS image. The ntfs_compressed_pwrite function processes insufficiently validated NTFS metadata while writing compressed attribute data, allowing a heap buffer to be overrun. Exploitation requires local access to a setuid-root ntfs-3g binary or physical access to storage that the host processes, and successful exploitation can run code with elevated privileges.

CVSS severity7.8
High
EPSS probability0.45%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Heap-based buffer overflow in NTFS-3G before 2021.8.22 allows local users to execute privileged code via a crafted NTFS image. The ntfs_compressed_pwrite function processes insufficiently validated NTFS metadata while writing compressed attribute data, allowing a heap buffer to be overrun. Exploitation requires local access to a setuid-root ntfs-3g binary or physical access to storage that the host processes, and successful exploitation can run code with elevated privileges.

The record

CVE
CVE-2021-39261
Published
Sep 7, 2021
Updated
Dec 5, 2025
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-787, CWE-20, T1068
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Sep 7, 2021CVE publishedPublication date reported by the CVE source.
  2. Dec 5, 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

6.7CISA-ADPCVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
7.8NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
6.9NIST NVDAV:L/AC:M/Au:N/C:C/I:C/A:C

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-787Out-of-bounds Write
CWE-20Improper Input Validation
T1068Exploitation for Privilege Escalation

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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