Nltk Nltk
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 `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.
What this means for your business
- It affects Nltk. It matters if your company, or a supplier that handles your data, runs it.
- An attacker can use it remotely, over a network, without a login, but only after tricking someone into an action such as opening a file or a link.
- FIRST's prediction model gives it a 0.2% chance of attack attempts being seen in the next 30 days, ranking above 10% of all known flaws.
What to do
- 1Check whether your company or your suppliers run Nltk, and which version. The affected versions are listed further down this page.
- 2If you do, follow the vendor's guidance. No patch reference has been published yet.
Not sure if your company is exposed?
Fastnexa’s certified penetration testers can check whether attackers could use this flaw, or others like it, against your websites, apps and network. The full test is free for our first 10 founding clients until 31 December 2026.
Scoring
- CVSS
- 6.5 (v3.1)
- Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N- Weakness
- CWE-284
- Assigned by
- security@huntr.dev
Dates
- Published
- 2026-08-07
- Last modified
- 2026-09-04
- Sources
- NVD
Affected products
- Nltk Nltk- 3.9.4
As listed in the NVD configuration data. Not a statement about your estate.