NLTK before 3.9.3 Missing Post-Download Integrity Verification

{
  "id": "86adb8ce734e335801a5e267f624f06e0dfa9672a0ae635225378aa6edb079a8",
  "url": "https://osv.dev/vulnerability/CVE-2026-63310",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "NLTK before 3.9.3 Missing Post-Download Integrity Verification",
    "summary": "NLTK before 3.9.3 fails to verify file integrity after downloading packages and before extraction in the downloader module. Attackers can perform man-in-the-middle attacks or DNS poisoning to inject malicious package contents that are extracted without validation.",
    "evidence": "osv:CVE-2026-63310",
    "products": [],
    "severity": "critical",
    "structured": {
      "id": "CVE-2026-63310",
      "aliases": [
        "CVE-2026-12259",
        "CVE-2026-63310",
        "GHSA-5wp5-5229-5g6q",
        "GHSA-gf32-cmjh-8m9v",
        "PYSEC-2026-3729",
        "PYSEC-2026-4318"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/nltk/nltk",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "4154eb85e832f266660a09286c7e37e308292284"
                }
              ],
              "database_specific": {
                "cpe": "cpe:2.3:a:nltk:nltk:*:*:*:*:*:*:*:*",
                "source": [
                  "AFFECTED_FIELD",
                  "CPE_RANGE"
                ],
                "extracted_events": [
                  {
                    "introduced": "0"
                  },
                  {
                    "fixed": "3.9.3"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v3.9.2",
            "3.9.2",
            "3.9.1",
            "3.9",
            "3.8.2",
            "3.8.1",
            "3.8",
            "3.7",
            "3.6.7",
            "3.6.6",
            "3.6.5",
            "3.6.2",
            "3.6.1",
            "3.6",
            "3.5",
            "3.5b1",
            "3.4.4",
            "3.4.3",
            "3.4.1",
            "3.4",
            "3.3",
            "3.2.5",
            "3.2.4",
            "3.2.3",
            "3.2.2",
            "3.2.1",
            "3.2",
            "3.1",
            "3.0.5",
            "3.0.4",
            "3.0.3",
            "3.0.2",
            "3.0.0b1",
            "3.0a4",
            "2.0.1rc4",
            "2.0.1rc3",
            "2.0.1rc2",
            "2.0.1rc1"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-63310.json"
          }
        }
      ],
      "modified": "2026-10-16T10:56:05.808390648Z",
      "provider": "osv",
      "references": [
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/63xxx/CVE-2026-63310.json",
        "https://github.com/nltk/nltk/security/advisories/GHSA-5wp5-5229-5g6q",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-63310",
        "https://www.vulncheck.com/advisories/nltk-before-missing-post-download-integrity-verification"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-494"
        ],
        "cna_assigner": "VulnCheck",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/63xxx/CVE-2026-63310.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-12259",
        "evidence": "/aliases"
      },
      {
        "value": "CVE-2026-63310",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 340602,
  "published_at": "2026-08-22T14:12:39.36+00:00"
}