CVE-2026-12261: Gptline · NLTK downloader allows cross-package resource and model poisoning
Affects gptlineSource GCVE Database
Not known to be exploited · CVSS 5.3 Medium : upgrade to 1.0.8_22 when convenient.
Data as of 5 Nov 2026, 23:24 UTC
- EPSS
- 0.2% chance of exploitation in 30 days – higher than 11% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
- Patch
- Available – fixed in 3.10.0, 3.8.1_1, 1.0.8_22
CVSS:3.0/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:NExploitation evidence
Disclosed: evidence found.
CVE published 7 Aug 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 5 Nov 2026.
What to do
Upgrade gptline to 1.0.8_22; nltk to 3.10.0; safety to 3.8.1_1.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
PyPInltkpkg:pypi/nltkOther threats | Affected
| Fixed in– |
| PyPInltk | Affected
| Fixed in
|
Homebrewsafetypkg:brew/safetyOther threats | Affected
| Fixed in
|
Homebrewgptlinepkg:brew/gptlineOther threats | Affected
| Fixed in
|
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
AI-suggested
A patch is available for this vulnerability. Users should upgrade to a fixed version of nltk beyond 3.9.4 and 3.10.0 to prevent cross-package resource poisoning. Until patched, avoid installing untrusted packages via nltk.downloader and consider isolating environments to limit impact. Check the official vendor advisory for specific fixed versions and update instructions.
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.
References
- nvd.nist.gov/vuln/detail/CVE-2026-12261 (opens in a new tab)
- huntr.com/bounties/8b8c381e-08a8-4e4f-bb46-a320c96a364f (opens in a new tab)
- github.com/nltk/nltk/pull/3625 (opens in a new tab)
- github.com/nltk/nltk/commit/7a5740af89feeb739193db766e11e85dfe78339c (opens in a new tab)
- github.com/nltk/nltk (opens in a new tab)
- github.com/nltk/nltk/releases/tag/v3.10.0 (opens in a new tab)
- github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2026-3954.yaml (opens in a new tab)