{"id":"CVE-2026-12259","state":"PUBLISHED","title":"Improper Input Validation in nltk/nltk","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.","publishedAt":"2026-08-03T07:09:35.262Z","updatedAt":"2026-08-03T14:59:01.815Z","severity":{"score":5.3,"label":"Medium","version":"3.0","vector":"CVSS:3.0/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N","source":"@huntr_ai"},"assigner":"@huntr_ai","products":["nltk nltk/nltk"],"affected":[{"vendor":"nltk","product":"nltk/nltk","versions":[{"version":"unspecified","status":"affected","lessThanOrEqual":"latest","versionType":"custom"}]}],"references":["https://huntr.com/bounties/659ccf6d-12d4-4d4a-84c0-078633c35a5d"],"weaknesses":["CWE-494"],"ingestedAt":"2026-10-29T20:10:52.580Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/12xxx/CVE-2026-12259.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-12259","state":"PUBLISHED","datePublished":"2026-08-03T07:09:35.262Z","dateUpdated":"2026-08-03T14:59:01.815Z","assignerShortName":"@huntr_ai","assignerOrgId":"c09c270a-b464-47c1-9133-acb35b22c19a","dateReserved":"2026-06-15T09:55:01.162Z"},"containers":{"cna":{"title":"Improper Input Validation in nltk/nltk","descriptions":[{"lang":"en","value":"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."}],"affected":[{"vendor":"nltk","product":"nltk/nltk","versions":[{"version":"unspecified","status":"affected","lessThanOrEqual":"latest","versionType":"custom"}]}],"references":[{"url":"https://huntr.com/bounties/659ccf6d-12d4-4d4a-84c0-078633c35a5d"}],"metrics":[{"cvssV3_0":{"version":"3.0","attackComplexity":"HIGH","attackVector":"NETWORK","availabilityImpact":"NONE","confidentialityImpact":"NONE","integrityImpact":"HIGH","privilegesRequired":"NONE","scope":"UNCHANGED","userInteraction":"REQUIRED","vectorString":"CVSS:3.0/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N","baseScore":5.3,"baseSeverity":"MEDIUM"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-494","type":"CWE","lang":"en","description":"CWE-494 Download of Code Without Integrity Check"}]}],"providerMetadata":{"shortName":"@huntr_ai","orgId":"c09c270a-b464-47c1-9133-acb35b22c19a","dateUpdated":"2026-08-03T07:09:35.262Z"},"source":{"advisory":"659ccf6d-12d4-4d4a-84c0-078633c35a5d","discovery":"EXTERNAL"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-08-03T14:55:19.698104Z","id":"CVE-2026-12259","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-08-03T14:59:01.815Z"}}]}}}