GHSA-4xw3-jf9x-x7mf: Duplicate Advisory Downloader.download Follows Hardlinks And Overwrites Vulnerability

MODERATE
Share
CVSS 7.1
CWE-59
Published
Advisory Summary

GHSA-4xw3-jf9x-x7mf is a MODERATE (CVSS 7.1) downloader.download follows hardlinks and overwrites vulnerability (CWE-59: Improper Link Resolution Before File Access ('Link Following')) affecting Duplicate Advisory libraries in the PyPI ecosystem. The issue involves downloader.download follows hardlinks and overwrites outside-root files. Remediation is available in the latest vendor maintenance releases.

GHSA-4xw3-jf9x-x7mf at a Glance

CVE Identifier N/A
GHSA Identifier GHSA-4xw3-jf9x-x7mf
Severity MODERATE
CVSS v3.1 Base Score 7.1
CWE Classification CWE-59: Improper Link Resolution Before File Access ('Link Following')
Affected Product Duplicate Advisory
Package Ecosystem PyPI
Published Date
Last Updated

Security Impact

CVSS: 7.1

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H).

Attack Vector Local (AV:L)
Attack Complexity Low (AC:L)
Privileges Required Low (PR:L)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity High (I:H)
Availability High (A:H)

How to Fix GHSA-4xw3-jf9x-x7mf

To remediate this vulnerability, upgrade all affected Duplicate Advisory dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

nltk fixed: Latest secure release 
pip install nltk>=Latest secure release
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

pip show nltk

How to Check if You Are Affected

To determine whether your Python environment is affected by GHSA-4xw3-jf9x-x7mf, inspect your installed packages using pip:

pip show nltk

Analyze the terminal output to locate any version of Duplicate Advisory in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than the patched release), your application is affected.

Note: The pip show nltk command checks currently installed packages in your active Python environment.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-59: Improper Link Resolution Before File Access ('Link Following'), where the product attempts to access a file based on the filename, but it does not properly prevent that filename from identifying a link or shortcut that resolves to an unintended resource. In Duplicate Advisory, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

## Duplicate Advisory This advisory has been withdrawn because it is a duplicate of GHSA-f794-5jv7-7672. This link is maintained to preserve external references. ## Original Description NLTK versions before 3.10.3 contain a filesystem containment bypass vulnerability in the Downloader.download and Downloader.incr_download methods that allows attackers to overwrite files outside the install root through pre-existing hardlinks. Attackers with write access to a shared downloader directory can create hardlinks pointing to outside-root files that are then overwritten during normal package extraction, mutating files outside the intended install tree.

GHSA-4xw3-jf9x-x7mf Affected Duplicate Advisory Versions

1 component(s)
Product / Package Ecosystem Affected Versions Fixed Version
nltk
pypi/nltk
PyPI
≤ 3.10.2

References

GitHub Advisory / Wiki ADVISORY
https://github.com/nltk/nltk/security/advisories/GHSA-f794-5jv7-7672
NVD — GHSA-4xw3-jf9x-x7mf NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-81727
www.vulncheck.com/advisories/nltk-bef... WEB
https://www.vulncheck.com/advisories/nltk-before-3.10.3-hardlink-file-overwrite-via-downloader

Frequently Asked Questions

What is GHSA-4xw3-jf9x-x7mf?
GHSA-4xw3-jf9x-x7mf is a security vulnerability in Duplicate Advisory involving Downloader.download follows hardlinks and overwrites outside-root files under CWE-59: Improper Link Resolution Before File Access ('Link Following').
Which Duplicate Advisory versions are affected?
Affected versions include releases prior to current release patches across affected packages: nltk.
What version fixes GHSA-4xw3-jf9x-x7mf?
Upgrading to current release patches (or the latest patched release for your respective branch) resolves the vulnerability.
Is nltk affected?
Yes, nltk is affected in releases prior to Latest secure release. Upgrade your dependency to Latest secure release or later.
What is the CVSS score of GHSA-4xw3-jf9x-x7mf?
GHSA-4xw3-jf9x-x7mf has a CVSS v3.1 base score of 7.1 (MODERATE) with vector string CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H.
What CWE is associated with GHSA-4xw3-jf9x-x7mf?
GHSA-4xw3-jf9x-x7mf is classified under CWE-59: Improper Link Resolution Before File Access ('Link Following') (The product attempts to access a file based on the filename, but it does not properly prevent that filename from identifying a link or shortcut that resolves to an unintended resource.).
How can I check PyPI dependencies for GHSA-4xw3-jf9x-x7mf?
Run the dependency tree command: 'pip show nltk'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-4xw3-jf9x-x7mf",
  "modified" : "2026-09-02T14:35:28Z",
  "published" : "2026-08-27T18:32:30Z",
  "withdrawn" : "2026-09-02T14:35:28Z",
  "aliases" : [ ],
  "summary" : "Duplicate Advisory:  Downloader.download follows hardlinks and overwrites outside-root files",
  "details" : "## Duplicate Advisory\n\nThis advisory has been withdrawn because it is a duplicate of GHSA-f794-5jv7-7672. This link is maintained to preserve external references.\n\n## Original Description\nNLTK versions before 3.10.3 contain a filesystem containment bypass vulnerability in the Downloader.download and Downloader.incr_download methods that allows attackers to overwrite files outside the install root through pre-existing hardlinks. Attackers with write access to a shared downloader directory can create hardlinks pointing to outside-root files that are then overwritten during normal package extraction, mutating files outside the intended install tree.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "nltk"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "last_affected" : "3.10.2"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/nltk/nltk/security/advisories/GHSA-f794-5jv7-7672"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-81727"
  }, {
    "type" : "WEB",
    "url" : "https://www.vulncheck.com/advisories/nltk-before-3.10.3-hardlink-file-overwrite-via-downloader"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-59" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-02T14:35:28Z",
    "nvd_published_at" : "2026-08-27T17:21:03Z"
  }
}