CVE-2026-0847: Nltk Path Traversal Vulnerability

HIGH
Advisory Identifier: GHSA-68j8-pq59-fqgm
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CVSS 8.6
CWE-22
Published
Advisory Summary

CVE-2026-0847 is a HIGH (CVSS 8.6) path traversal vulnerability (CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')) affecting Nltk libraries in the PyPI ecosystem. The issue involves nltk has a path traversal issue. Remediation is available in the latest vendor maintenance releases.

CVE-2026-0847 at a Glance

CVE Identifier CVE-2026-0847
GHSA Identifier GHSA-68j8-pq59-fqgm
Severity HIGH
CVSS v3.1 Base Score 8.6
CWE Classification CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
Affected Product Nltk
Package Ecosystem PyPI
Published Date
Last Updated

Security Impact

CVSS: 8.6

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:L).

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

How to Fix CVE-2026-0847

To remediate this vulnerability, upgrade all affected Nltk 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 CVE-2026-0847, inspect your installed packages using pip:

pip show nltk

Analyze the terminal output to locate any version of Nltk 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-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal'), where the product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory. In Nltk, 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

A vulnerability in NLTK versions up to and including 3.9.2 allows arbitrary file read via path traversal in multiple CorpusReader classes, including WordListCorpusReader, TaggedCorpusReader, and BracketParseCorpusReader. These classes fail to properly sanitize or validate file paths, enabling attackers to traverse directories and access sensitive files on the server. This issue is particularly critical in scenarios where user-controlled file inputs are processed, such as in machine learning APIs, chatbots, or NLP pipelines. Exploitation of this vulnerability can lead to unauthorized access to sensitive files, including system files, SSH private keys, and API tokens, and may potentially escalate to remote code execution when combined with other vulnerabilities.

CVE-2026-0847 Affected Nltk Versions

1 component(s)
Product / Package Ecosystem Affected Versions Fixed Version
nltk
pypi/nltk
PyPI
≤ 3.9.2

References

NVD — CVE-2026-0847 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-0847
Nltk Source Repository REPOSITORY
https://github.com/nltk/nltk
Nltk Source Repository REPOSITORY
https://github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2026-98.yaml
huntr.com/bounties/fc69914f-3... WEB
https://huntr.com/bounties/fc69914f-36a9-4c18-8503-10013b39f966

Frequently Asked Questions

What is CVE-2026-0847?
CVE-2026-0847 is a security vulnerability in Nltk involving NLTK has a Path Traversal issue under CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal').
Which Nltk versions are affected?
Affected versions include releases prior to current release patches across affected packages: nltk.
What version fixes CVE-2026-0847?
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 CVE-2026-0847?
CVE-2026-0847 has a CVSS v3.1 base score of 8.6 (HIGH) with vector string CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:L.
What CWE is associated with CVE-2026-0847?
CVE-2026-0847 is classified under CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') (The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.).
How can I check PyPI dependencies for CVE-2026-0847?
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-68j8-pq59-fqgm",
  "modified" : "2026-06-08T18:36:26Z",
  "published" : "2026-03-04T21:32:45Z",
  "aliases" : [ "CVE-2026-0847" ],
  "summary" : "NLTK has a Path Traversal issue",
  "details" : "A vulnerability in NLTK versions up to and including 3.9.2 allows arbitrary file read via path traversal in multiple CorpusReader classes, including WordListCorpusReader, TaggedCorpusReader, and BracketParseCorpusReader. These classes fail to properly sanitize or validate file paths, enabling attackers to traverse directories and access sensitive files on the server. This issue is particularly critical in scenarios where user-controlled file inputs are processed, such as in machine learning APIs, chatbots, or NLP pipelines. Exploitation of this vulnerability can lead to unauthorized access to sensitive files, including system files, SSH private keys, and API tokens, and may potentially escalate to remote code execution when combined with other vulnerabilities.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:L"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "nltk"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "last_affected" : "3.9.2"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-0847"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/nltk/nltk"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2026-98.yaml"
  }, {
    "type" : "WEB",
    "url" : "https://huntr.com/bounties/fc69914f-36a9-4c18-8503-10013b39f966"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-22" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-06T19:18:16Z",
    "nvd_published_at" : "2026-03-04T19:16:10Z"
  }
}