CVE-2026-81727Public exploitHinoki check available

Outside-root file overwrite via pre-existing hardlinks

Published Aug 27, 2026 · Updated Aug 27, 2026

Filesystem containment bypass in NLTK before 3.10.3 allows local users to overwrite outside-root files through pre-existing hardlinks. Downloader.download and Downloader.incr_download accept an existing hardlink as an in-root extraction target and write package data through it to the linked inode. Exploitation requires write access to a shared downloader directory on the target file's filesystem and can modify or destroy data accessible to the downloader process.

CVSS severity7.1
High
EPSS probability0.14%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

Filesystem containment bypass in NLTK before 3.10.3 allows local users to overwrite outside-root files through pre-existing hardlinks. Downloader.download and Downloader.incr_download accept an existing hardlink as an in-root extraction target and write package data through it to the linked inode. Exploitation requires write access to a shared downloader directory on the target file's filesystem and can modify or destroy data accessible to the downloader process.

The record

CVE
CVE-2026-81727
Published
Aug 27, 2026
Updated
Aug 27, 2026
Vendor
NLTK Project
Product
NLTK
Classifications
CWE-61, CWE-59, CWE-73, T1565.001
Attack vector
local
Privileges
Unavailable

Timeline

How it unfolded

  1. Aug 27, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 27, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <3.10.3

What conditions does exploitation require?

Attack vectorlocal
Required privilegesUnavailable in this record.

What is affected?

NLTK Project · NLTKversion=0 <3.10.3

Published CVSS scores

7.1GitHub Security AdvisoryCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/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.

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

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
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-61UNIX Symbolic Link (Symlink) Following
CWE-59Improper Link Resolution Before File Access ('Link Following')
CWE-73External Control of File Name or Path
T1565.001Stored Data Manipulation

Public exploit references

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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