Vulnerability · Published Aug 7, 2026 · Assigned by @huntr_ai
CVE-2026-12261Improper Access Control in nltk/nltk
Medium 5.3
In plain English
A medium-severity improper access control in nltk/nltk from nltk. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 11% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | nltk | no fix listed | DEBIAN-CVE-2026-12261 |
| Debian:13 | nltk | no fix listed | DEBIAN-CVE-2026-12261 |
| Debian:14 | nltk | no fix listed | DEBIAN-CVE-2026-12261 |
| PyPI | nltk | 3.10.0 | GHSA-ffj6-66c4-86gw |
| PyPI | nltk | 3.10.0 | PYSEC-2026-3954 |
| Ubuntu:26.10 | nltk | no fix listed | UBUNTU-CVE-2026-12261 |
Affected products (as reported)
Weakness: CWE-284 · Vector: CVSS:3.0/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N