{"cve":"CVE-2026-12261","nvd":{"published":"2026-08-07T07:16:26.377","modified":"2026-10-23T21:10:00.157","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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N","score":6.5},"cwes":["CWE-284"],"references":["https://huntr.com/bounties/8b8c381e-08a8-4e4f-bb46-a320c96a364f","https://huntr.com/bounties/8b8c381e-08a8-4e4f-bb46-a320c96a364f"],"products":["nltk:nltk"],"source":"nvd","synced_at":"2026-10-24T16:53:34.184483516+00:00"},"epss":{"cve":"CVE-2026-12261","score":0.00211,"percentile":0.11208,"date":"2026-10-25"},"kev":null,"osv":[{"id":"GHSA-ffj6-66c4-86gw","url":"https://osv.dev/vulnerability/GHSA-ffj6-66c4-86gw","summary":"NLTK downloader allows cross-package resource and model poisoning","modified":"2026-10-02T23:40:50.637389089Z","packages":[{"ecosystem":"PyPI","name":"nltk","purl":"pkg:pypi/nltk","ranges":["<3.10.0"],"fixed":["3.10.0"]}]},{"id":"PYSEC-2026-3954","url":"https://osv.dev/vulnerability/PYSEC-2026-3954","summary":"","modified":"2026-10-15T14:45:11.781131372Z","packages":[{"ecosystem":"PyPI","name":"nltk","purl":"pkg:pypi/nltk","ranges":["<3.10.0"],"fixed":["3.10.0"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}