1. Home
  2. CVE Database
  3. CVE-2026-12261
MEDIUM · 5.3

CVE-2026-12261

A vulnerability in `nltk.downloader` in nltk/nltk versions <= 3.9.4 allows for cross-package resource and model poisoning. The downloader extracts package archives into shared namespaces such as `corp...

Vulnerability Description

A vulnerability in `nltk.downloader` in nltk/nltk versions <= 3.9.4 allows for cross-package resource and model poisoning. The downloader extracts package archives into shared namespaces such as `corpora/` and `taggers/` instead of package-isolated roots, and validates package integrity only after the archive has been written and extracted. This design flaw enables one package to overwrite another package's trusted resources within the same namespace, making the changes immediately active through ordinary NLTK APIs. This issue persists across fresh interpreter restarts and can affect downstream workflows, including machine learning pipelines and reproducibility-sensitive environments.

CVSS Score

5.3

MEDIUM

CVSS:3.0/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N
Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
NONE
User Interaction
REQUIRED
Scope
UNCHANGED
Confidentiality
NONE
Integrity
HIGH
Availability
NONE

Related Weaknesses (CWE)

CWE-284

References

FAQ

What is CVE-2026-12261?

CVE-2026-12261 is a vulnerability with a CVSS score of 5.3 (MEDIUM). A vulnerability in `nltk.downloader` in nltk/nltk versions <= 3.9.4 allows for cross-package resource and model poisoning. The downloader extracts package archives into shared namespaces such as `corp...

How severe is CVE-2026-12261?

CVE-2026-12261 has been rated MEDIUM with a CVSS base score of 5.3/10. Review the CVSS metrics above for detailed severity breakdown.

Is there a patch for CVE-2026-12261?

Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.