CVE-2026-63310: Duplicate Advisory NLTK: Missing Post-Download Integrity Verification Vulnerability

CRITICAL
Advisory Identifier: GHSA-gf32-cmjh-8m9v
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CVSS 7.1
CWE-494
Published
Advisory Summary

CVE-2026-63310 is a CRITICAL (CVSS 7.1) nltk: missing post-download integrity verification vulnerability (CWE-494: Download of Code Without Integrity Check) affecting Duplicate Advisory libraries in the PyPI ecosystem. The issue involves nltk: missing post-download integrity verification allows malicious package injection. Remediation is available in the latest vendor maintenance releases.

CVE-2026-63310 at a Glance

CVE Identifier CVE-2026-63310
GHSA Identifier GHSA-gf32-cmjh-8m9v
Severity CRITICAL
CVSS v3.1 Base Score 7.1
CWE Classification CWE-494: Download of Code Without Integrity Check
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:N/AC:H/PR:N/UI:R/S:U/C:L/I:H/A:H).

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

How to Fix CVE-2026-63310

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 CVE-2026-63310, 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-494: Download of Code Without Integrity Check, where the product downloads source code or an executable from a remote location and executes the code without sufficiently verifying the origin and integrity of the code. 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-5wp5-5229-5g6q. This link is maintained to preserve external references. ## Original Description NLTK before 3.9.3 fails to verify file integrity after downloading packages and before extraction in the downloader module. Attackers can perform man-in-the-middle attacks or DNS poisoning to inject malicious package contents that are extracted without validation.

CVE-2026-63310 Affected Duplicate Advisory Versions

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

References

GitHub Advisory / Wiki ADVISORY
https://github.com/nltk/nltk/security/advisories/GHSA-5wp5-5229-5g6q
NVD — CVE-2026-63310 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-63310
www.vulncheck.com/advisories/nltk-bef... WEB
https://www.vulncheck.com/advisories/nltk-before-missing-post-download-integrity-verification

Frequently Asked Questions

What is CVE-2026-63310?
CVE-2026-63310 is a security vulnerability in Duplicate Advisory involving NLTK: Missing Post-Download Integrity Verification Allows Malicious Package Injection under CWE-494: Download of Code Without Integrity Check.
Which Duplicate Advisory versions are affected?
Affected versions include releases prior to current release patches across affected packages: nltk.
What version fixes CVE-2026-63310?
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-2026-63310?
CVE-2026-63310 has a CVSS v3.1 base score of 7.1 (CRITICAL) with vector string CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:H/A:H.
What CWE is associated with CVE-2026-63310?
CVE-2026-63310 is classified under CWE-494: Download of Code Without Integrity Check (The product downloads source code or an executable from a remote location and executes the code without sufficiently verifying the origin and integrity of the code.).
How can I check PyPI dependencies for CVE-2026-63310?
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-gf32-cmjh-8m9v",
  "modified" : "2026-09-09T16:33:54Z",
  "published" : "2026-08-22T15:31:03Z",
  "withdrawn" : "2026-09-09T16:33:54Z",
  "aliases" : [ "CVE-2026-63310" ],
  "summary" : "Duplicate Advisory: NLTK: Missing Post-Download Integrity Verification Allows Malicious Package Injection",
  "details" : "## Duplicate Advisory\n\nThis advisory has been withdrawn because it is a duplicate of GHSA-5wp5-5229-5g6q. This link is maintained to preserve external references.\n\n## Original Description\nNLTK before 3.9.3 fails to verify file integrity after downloading packages and before extraction in the downloader module. Attackers can perform man-in-the-middle attacks or DNS poisoning to inject malicious package contents that are extracted without validation.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:H/A:H"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/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" : "3.9.2"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/nltk/nltk/security/advisories/GHSA-5wp5-5229-5g6q"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-63310"
  }, {
    "type" : "WEB",
    "url" : "https://www.vulncheck.com/advisories/nltk-before-missing-post-download-integrity-verification"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-494" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-09T16:33:54Z",
    "nvd_published_at" : "2026-08-22T15:16:19Z"
  }
}