{"cve":"CVE-2026-12259","nvd":{"published":"2026-08-03T08:17:17.880","modified":"2026-10-23T22:10:00.160","status":"Analyzed","description":"In nltk version 3.9.4, the `nltk.downloader.Downloader._download_package()` function writes downloaded package bytes to disk and may extract them before enforcing SHA-256 or MD5 checksum validation. This allows an attacker to tamper with the package response body for `info.url` through a compromised mirror, malicious proxy, or other source-substitution condition, leading to the installation of attacker-controlled package bytes. The vulnerability can result in malicious corpus or model content being trusted by downstream users or applications.","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-494"],"references":["https://huntr.com/bounties/659ccf6d-12d4-4d4a-84c0-078633c35a5d"],"products":["nltk:nltk"],"source":"nvd","synced_at":"2026-10-24T16:53:34.184483516+00:00"},"epss":{"cve":"CVE-2026-12259","score":0.00101,"percentile":0.00893,"date":"2026-10-25"},"kev":null,"osv":[{"id":"GHSA-5wp5-5229-5g6q","url":"https://osv.dev/vulnerability/GHSA-5wp5-5229-5g6q","summary":"NLTK: Missing Post-Download Integrity Verification Allows Malicious Package Injection","modified":"2026-10-16T10:56:05.808390648Z","packages":[{"ecosystem":"PyPI","name":"nltk","purl":"pkg:pypi/nltk","ranges":["<3.9.3"],"fixed":["3.9.3"]}]},{"id":"PYSEC-2026-3729","url":"https://osv.dev/vulnerability/PYSEC-2026-3729","summary":"","modified":"2026-10-16T10:56:05.808390648Z","packages":[{"ecosystem":"PyPI","name":"nltk","purl":"pkg:pypi/nltk","ranges":["<3.9.3"],"fixed":["3.9.3"]}]},{"id":"PYSEC-2026-4318","url":"https://osv.dev/vulnerability/PYSEC-2026-4318","summary":"","modified":"2026-10-16T10:56:05.808390648Z","packages":[{"ecosystem":"PyPI","name":"nltk","purl":"pkg:pypi/nltk","ranges":["<=3.9.4"],"fixed":[]}]}],"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."]}