Reference page — cumulative record through Sunday, October 4, 2026 UTC. Reference pages update as the archive grows; only dated daily editions are immutable pages of record.

CVE-2026-12261

CVE-2026-12261MEDIUM

nltk nltk/nltk — Improper Access Control in nltk/nltk

  AV  AC  PR  UI  S  C  I  A   CVSS    EPSS   %ile   KEV
   N   L   N   R  U  N  H  N    6.5   .0021    9.5     —

AFFECTED
  Product    Versions       Fixed
  nltk/nltk  unspecified –  —

TIMELINE
  Jun 15  Reserved by @huntr_ai
  Aug 7   Published (CNA: @huntr_ai)
  Sep 4   RESCORED — CVE-2026-12261 (nltk/nltk). CVSS 5.3 → 6.5 (NVD).

CWE-284 · CNA: @huntr_ai · CVSS v3.1 · 1 reference · NVD status: Analyzed

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.

Lifecycle

Complete event history — 3 events, chronological
Date	Event	Detail
June 15, 2026	Reserved	Reserved by @huntr_ai
August 7, 2026	Published	Published (CNA: @huntr_ai)
September 4, 2026	RESCORED	RESCORED — CVE-2026-12261 (nltk/nltk). CVSS 5.3 → 6.5 (NVD).

Affected

Affected products and packages — 1 row
Vendor	Product / Package	Ecosystem	Version introduced	Fixed
nltk	nltk/nltk	—	unspecified	—

Weaknesses

CWE-284

References (1)

https://huntr.com/bounties/8b8c381e-08a8-4e4f-bb46-a320c96a364f [Permissions Required]

Authoritative record: CVE-2026-12261 at cve.org

Vendors: nltk

Weaknesses: CWE-284

About this page

This is a reference page, not a dated page of record. It assembles the complete lifecycle of CVE-2026-12261 from the CVE Program record, NVD enrichment, the CISA KEV catalog, EPSS, and OSV advisories. The box score's numbers (CVSS, EPSS, KEV status) are current as of Sunday, October 4, 2026 UTC and are re-derived as the archive grows; only dated daily editions are immutable pages of record. The authoritative source for this identifier is cve.org.