CVE-2026-0846: Nltk NLTK Has Arbitrary File Read Vulnerability

HIGH
Advisory Identifier: GHSA-h8wq-7xc4-p3qx
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CVSS 8.6
CWE-36
Published
Advisory Summary

CVE-2026-0846 is a HIGH (CVSS 8.6) nltk has arbitrary file read vulnerability (CWE-36: Absolute Path Traversal) affecting Nltk libraries in the PyPI ecosystem. The issue involves nltk has arbitrary file read via absolute path input in nltk.util.filestring(). Remediation is available by upgrading affected packages to version 3.9.3.

CVE-2026-0846 at a Glance

CVE Identifier CVE-2026-0846
GHSA Identifier GHSA-h8wq-7xc4-p3qx
Severity HIGH
CVSS v3.1 Base Score 8.6
CWE Classification CWE-36: Absolute 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-2026-0846

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: 3.9.3 
pip install nltk>=3.9.3
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-2026-0846, 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 3.9.3), 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-36: Absolute Path Traversal, where the product uses external input to construct a pathname that should be within a restricted directory, but it does not properly neutralize absolute path sequences such as "/abs/path" that can resolve to a location that is outside of that 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 the `filestring()` function of the `nltk.util` module in nltk version 3.9.2 allows arbitrary file read due to improper validation of input paths. The function directly opens files specified by user input without sanitization, enabling attackers to access sensitive system files by providing absolute paths or traversal paths. This vulnerability can be exploited locally or remotely, particularly in scenarios where the function is used in web APIs or other interfaces that accept user-supplied input.

CVE-2026-0846 Affected Nltk Versions

1 component(s)
Fixed Versions:
3.9.3
Product / Package Ecosystem Affected Versions Fixed Version
nltk
pypi/nltk
PyPI
< 3.9.3
3.9.3

References

NVD — CVE-2026-0846 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-0846
Nltk Source Repository REPOSITORY
https://github.com/nltk/nltk/pull/3485
Security Fix Commit FIX COMMIT
https://github.com/nltk/nltk/commit/b2e1164bf89277f79b65406c829b99fb20ca1974
Nltk Source Repository REPOSITORY
https://github.com/nltk/nltk
Nltk Source Repository REPOSITORY
https://github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2026-97.yaml
huntr.com/bounties/007b84f8-4... WEB
https://huntr.com/bounties/007b84f8-418e-4300-99d0-bf504c2f97eb

Frequently Asked Questions

What is CVE-2026-0846?
CVE-2026-0846 is a security vulnerability in Nltk involving NLTK has Arbitrary File Read via Absolute Path Input in nltk.util.filestring() under CWE-36: Absolute Path Traversal.
Which Nltk versions are affected?
Affected versions include releases prior to 3.9.3 across affected packages: nltk.
What version fixes CVE-2026-0846?
Upgrading to 3.9.3 (or the latest patched release for your respective branch) resolves the vulnerability.
Is nltk affected?
Yes, nltk is affected in releases prior to 3.9.3. Upgrade your dependency to 3.9.3 or later.
What is the CVSS score of CVE-2026-0846?
CVE-2026-0846 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-2026-0846?
CVE-2026-0846 is classified under CWE-36: Absolute Path Traversal (The product uses external input to construct a pathname that should be within a restricted directory, but it does not properly neutralize absolute path sequences such as "/abs/path" that can resolve to a location that is outside of that directory.).
How can I check PyPI dependencies for CVE-2026-0846?
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-h8wq-7xc4-p3qx",
  "modified" : "2026-06-08T18:36:48Z",
  "published" : "2026-03-09T21:31:38Z",
  "aliases" : [ "CVE-2026-0846" ],
  "summary" : "NLTK has Arbitrary File Read via Absolute Path Input in nltk.util.filestring()",
  "details" : "A vulnerability in the `filestring()` function of the `nltk.util` module in nltk version 3.9.2 allows arbitrary file read due to improper validation of input paths. The function directly opens files specified by user input without sanitization, enabling attackers to access sensitive system files by providing absolute paths or traversal paths. This vulnerability can be exploited locally or remotely, particularly in scenarios where the function is used in web APIs or other interfaces that accept user-supplied input.",
  "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"
      }, {
        "fixed" : "3.9.3"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-0846"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nltk/nltk/pull/3485"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nltk/nltk/commit/b2e1164bf89277f79b65406c829b99fb20ca1974"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/nltk/nltk"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2026-97.yaml"
  }, {
    "type" : "WEB",
    "url" : "https://huntr.com/bounties/007b84f8-418e-4300-99d0-bf504c2f97eb"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-36" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-18T01:14:15Z",
    "nvd_published_at" : "2026-03-09T20:16:05Z"
  }
}