CVE-2025-71408: Nltk NLTK Vulnerable To Eval Injection Vulnerability

HIGH
Advisory Identifier: GHSA-848c-c2cx-j7qx
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CVSS 7.8
CWE-95
Published
Advisory Summary

CVE-2025-71408 is a HIGH (CVSS 7.8) nltk vulnerable to eval injection vulnerability (CWE-95: Improper Neutralization of Directives in Dynamically Evaluated Code ('Eval Injection')) affecting Nltk libraries in the PyPI ecosystem. The issue involves nltk vulnerable to eval injection via collocations cli arguments. Remediation is available by upgrading affected packages to version 3.9.3.

CVE-2025-71408 at a Glance

CVE Identifier CVE-2025-71408
GHSA Identifier GHSA-848c-c2cx-j7qx
Severity HIGH
CVSS v3.1 Base Score 7.8
CWE Classification CWE-95: Improper Neutralization of Directives in Dynamically Evaluated Code ('Eval Injection')
Affected Product Nltk
Package Ecosystem PyPI
Published Date
Last Updated

Security Impact

CVSS: 7.8

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:H/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 High (C:H)
Integrity High (I:H)
Availability High (A:H)

How to Fix CVE-2025-71408

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-2025-71408, 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-95: Improper Neutralization of Directives in Dynamically Evaluated Code ('Eval Injection'), where the product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes code syntax before using the input in a dynamic evaluation call (e.g. "eval"). 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

NLTK (Natural Language Toolkit) before version 3.9.3 contains an eval injection vulnerability in the nltk.collocations module that allows an attacker who controls command-line arguments to execute arbitrary Python code. When collocations.py is invoked directly, the __main__ block passes command-line arguments directly to eval() as suffixes of BigramAssocMeasures without allowlist validation or sanitization, enabling an attacker to supply a Python expression that escapes the intended attribute lookup and executes arbitrary code including OS commands via the os module.

CVE-2025-71408 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-2025-71408 NVD
https://nvd.nist.gov/vuln/detail/CVE-2025-71408
Nltk Source Repository REPOSITORY
https://github.com/nltk/nltk/pull/3465
Security Fix Commit FIX COMMIT
https://github.com/nltk/nltk/commit/66f14096d952ec8f04934f515e027534bd4eb0ac
aydinnyunus.github.io/2026/06/07/command-... WEB
https://aydinnyunus.github.io/2026/06/07/command-injection-nltk-collocations-eval
Nltk Source Repository REPOSITORY
https://github.com/nltk/nltk
Nltk Release RELEASE
https://github.com/nltk/nltk/releases/tag/3.9.3
Nltk Source Repository REPOSITORY
https://github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2026-3657.yaml
www.vulncheck.com/advisories/nltk-eva... WEB
https://www.vulncheck.com/advisories/nltk-eval-injection-via-collocations-py-command-line-arguments

Frequently Asked Questions

What is CVE-2025-71408?
CVE-2025-71408 is a security vulnerability in Nltk involving NLTK vulnerable to Eval Injection via collocations CLI arguments under CWE-95: Improper Neutralization of Directives in Dynamically Evaluated Code ('Eval Injection').
Which Nltk versions are affected?
Affected versions include releases prior to 3.9.3 across affected packages: nltk.
What version fixes CVE-2025-71408?
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-2025-71408?
CVE-2025-71408 has a CVSS v3.1 base score of 7.8 (HIGH) with vector string CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H.
What CWE is associated with CVE-2025-71408?
CVE-2025-71408 is classified under CWE-95: Improper Neutralization of Directives in Dynamically Evaluated Code ('Eval Injection') (The product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes code syntax before using the input in a dynamic evaluation call (e.g. "eval").).
How can I check PyPI dependencies for CVE-2025-71408?
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-848c-c2cx-j7qx",
  "modified" : "2026-08-12T19:30:21Z",
  "published" : "2026-07-25T00:31:47Z",
  "aliases" : [ "CVE-2025-71408" ],
  "summary" : "NLTK vulnerable to Eval Injection via collocations CLI arguments",
  "details" : "NLTK (Natural Language Toolkit) before version 3.9.3 contains an eval injection vulnerability in the nltk.collocations module that allows an attacker who controls command-line arguments to execute arbitrary Python code. When collocations.py is invoked directly, the __main__ block passes command-line arguments directly to eval() as suffixes of BigramAssocMeasures without allowlist validation or sanitization, enabling an attacker to supply a Python expression that escapes the intended attribute lookup and executes arbitrary code including OS commands via the os module.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N"
  } ],
  "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-2025-71408"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nltk/nltk/pull/3465"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nltk/nltk/commit/66f14096d952ec8f04934f515e027534bd4eb0ac"
  }, {
    "type" : "WEB",
    "url" : "https://aydinnyunus.github.io/2026/06/07/command-injection-nltk-collocations-eval"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/nltk/nltk"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nltk/nltk/releases/tag/3.9.3"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2026-3657.yaml"
  }, {
    "type" : "WEB",
    "url" : "https://www.vulncheck.com/advisories/nltk-eval-injection-via-collocations-py-command-line-arguments"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-95" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-08-12T19:30:21Z",
    "nvd_published_at" : "2026-07-24T22:16:50Z"
  }
}