CVE catalog
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
- Severity
- Medium · CVSS 6.5
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N - Published
- Source
- [NVD] · [CVE record]
- EPSS
- 0.21% · Oct 25, 2026
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.
Vulnerable and fixed packages
Distribution-reported package versions and fixes. These do not depend on matching against the OpenFactory package catalog.
| Distribution | Package | Release | Version | Status |
|---|---|---|---|---|
| Debian | nltk | sid | 3.10.3-1 | vulnerable |
| Debian | nltk | forky | 3.10.3-1 | vulnerable |
| Debian | nltk | trixie | 3.9.1-2 | vulnerable |
| Debian | nltk | bookworm | 3.8-1 | vulnerable |
| Cpe | nltk | Not reported | Not reported | unknown |
| PyPI | nltk | Not reported | 0.8 | vulnerable |
| PyPI | nltk | Not reported | 0.9 | vulnerable |
| PyPI | nltk | Not reported | 0.9.3 | vulnerable |
| PyPI | nltk | Not reported | 0.9.4 | vulnerable |
| PyPI | nltk | Not reported | 0.9.5 | vulnerable |
| PyPI | nltk | Not reported | 0.9.6 | vulnerable |
| PyPI | nltk | Not reported | 0.9.7 | vulnerable |
| PyPI | nltk | Not reported | 0.9.8 | vulnerable |
| PyPI | nltk | Not reported | 0.9.9 | vulnerable |
| PyPI | nltk | Not reported | 2.0.1 | vulnerable |
| PyPI | nltk | Not reported | 2.0.1rc1 | vulnerable |
| PyPI | nltk | Not reported | 2.0.1rc2-git | vulnerable |
| PyPI | nltk | Not reported | 2.0.1rc3 | vulnerable |
| PyPI | nltk | Not reported | 2.0.1rc4 | vulnerable |
| PyPI | nltk | Not reported | 2.0.2 | vulnerable |
| PyPI | nltk | Not reported | 2.0.3 | vulnerable |
| PyPI | nltk | Not reported | 2.0.4 | vulnerable |
| PyPI | nltk | Not reported | 2.0.5 | vulnerable |
| PyPI | nltk | Not reported | 2.0b4 | vulnerable |
| PyPI | nltk | Not reported | 2.0b5 | vulnerable |
| PyPI | nltk | Not reported | 2.0b6 | vulnerable |
| PyPI | nltk | Not reported | 2.0b7 | vulnerable |
| PyPI | nltk | Not reported | 2.0b8 | vulnerable |
| PyPI | nltk | Not reported | 2.0b9 | vulnerable |
| PyPI | nltk | Not reported | 3.0.0 | vulnerable |
| PyPI | nltk | Not reported | 3.0.0b1 | vulnerable |
| PyPI | nltk | Not reported | 3.0.0b2 | vulnerable |
| PyPI | nltk | Not reported | 3.0.1 | vulnerable |
| PyPI | nltk | Not reported | 3.0.2 | vulnerable |
| PyPI | nltk | Not reported | 3.0.3 | vulnerable |
| PyPI | nltk | Not reported | 3.0.4 | vulnerable |
| PyPI | nltk | Not reported | 3.0.5 | vulnerable |
| PyPI | nltk | Not reported | 3.1 | vulnerable |
| PyPI | nltk | Not reported | 3.2 | vulnerable |
| PyPI | nltk | Not reported | 3.2.1 | vulnerable |
| PyPI | nltk | Not reported | 3.2.2 | vulnerable |
| PyPI | nltk | Not reported | 3.2.3 | vulnerable |
| PyPI | nltk | Not reported | 3.2.4 | vulnerable |
| PyPI | nltk | Not reported | 3.2.5 | vulnerable |
| PyPI | nltk | Not reported | 3.3 | vulnerable |
| PyPI | nltk | Not reported | 3.4 | vulnerable |
| PyPI | nltk | Not reported | 3.4.1 | vulnerable |
| PyPI | nltk | Not reported | 3.4.2 | vulnerable |
| PyPI | nltk | Not reported | 3.4.3 | vulnerable |
| PyPI | nltk | Not reported | 3.4.4 | vulnerable |
| PyPI | nltk | Not reported | 3.4.5 | vulnerable |
| PyPI | nltk | Not reported | 3.5 | vulnerable |
| PyPI | nltk | Not reported | 3.5b1 | vulnerable |
| PyPI | nltk | Not reported | 3.6 | vulnerable |
| PyPI | nltk | Not reported | 3.6.1 | vulnerable |
| PyPI | nltk | Not reported | 3.6.2 | vulnerable |
| PyPI | nltk | Not reported | 3.6.3 | vulnerable |
| PyPI | nltk | Not reported | 3.6.4 | vulnerable |
| PyPI | nltk | Not reported | 3.6.5 | vulnerable |
| PyPI | nltk | Not reported | 3.6.6 | vulnerable |
| PyPI | nltk | Not reported | 3.6.7 | vulnerable |
| PyPI | nltk | Not reported | 3.7 | vulnerable |
| PyPI | nltk | Not reported | 3.8 | vulnerable |
| PyPI | nltk | Not reported | 3.8.1 | vulnerable |
| PyPI | nltk | Not reported | 3.9 | vulnerable |
| PyPI | nltk | Not reported | 3.9.1 | vulnerable |
| PyPI | nltk | Not reported | 3.9.2 | vulnerable |
| PyPI | nltk | Not reported | 3.9.3 | vulnerable |
| PyPI | nltk | Not reported | 3.9.4 | vulnerable |
| PyPI | nltk | Not reported | 3.9b1 | vulnerable |
| PyPI | nltk | Not reported | 3.10.0 | fixed |
| Pip | nltk | Not reported | 3.10.0 | fixed |
Fixed-version evidence
| Distribution | Package | Type | Release | Fixed version | Urgency | Origin | Bugs |
|---|---|---|---|---|---|---|---|
| Debian | nltk | source | sid | (unfixed) | not yet assigned | Not reported | [1144456] |
| Debian | nltk | source | forky | (unfixed) | not yet assigned | Not reported | [1144456] |
| Debian | nltk | source | trixie | (unfixed) | not yet assigned | Not reported | [1144456] |
| Debian | nltk | source | bookworm | (unfixed) | not yet assigned | Not reported | [1144456] |
| PyPI | nltk | PyPI | Not reported | 3.10.0 | Not reported | PYSEC-2026-3954 | Not reported |
| Pip | nltk | pip | Not reported | 3.10.0 | Not reported | GHSA-FFJ6-66C4-86GW | Not reported |
Notes
[trixie] nltk: Minor issue [bookworm] nltk: Minor issue
OpenFactory catalog packages
[Debian 12 (Bookworm)]
- [python3-nltk]Affected
Source package: [nltk]
Details (2)
3.8-1· all · bookwormAffected
nvd · nltk · debian · bookworm; nvd · nltk · debian · 12
3.8-1· all · bookwormAffected
nvd · nltk · debian · bookworm; nvd · nltk · debian · 12
[Debian 13 (Trixie)]
- [python3-nltk]Affected
Source package: [nltk]
Details (2)
3.9.1-2· all · trixieAffected
nvd · nltk · debian · 13
3.9.1-2· all · trixieAffected
nvd · nltk · debian · 13
Observed:
References
- [https://huntr.com/bounties/8b8c381e-08a8-4e4f-bb46-a320c96a364f]
- [https://nvd.nist.gov/vuln/detail/CVE-2026-12261]
- [https://osv.dev/vulnerability/DEBIAN-CVE-2026-12261]
- [https://osv.dev/vulnerability/PYSEC-2026-3954]
- [https://security-tracker.debian.org/tracker/CVE-2026-12261]
- [https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-12261.json]
[Debian Security Tracker] · [FIRST EPSS] · [GitHub Advisory Database] · [National Vulnerability Database (NVD)] · [OSV Package Vulnerability Database] · [Red Hat security advisories and VEX]