GHSA-pv39-qrfq-g8gc.json

{
  "schema_version": "1.4.0",
  "id": "GHSA-pv39-qrfq-g8gc",
  "modified": "2026-08-03T09:32:38Z",
  "published": "2026-08-03T09:32:37Z",
  "aliases": [
    "CVE-2026-12259"
  ],
  "summary": "NLTK Checksum Validation Bypass in Package Downloads",
  "details": "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.",
  "severity": [
    {
      "type": "CVSS_V3",
      "score": "CVSS:3.0/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N"
    }
  ],
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "nltk"
      },
      "ranges": [
        {
          "type": "ECOSYSTEM",
          "events": [
            {
              "introduced": "0"
            }
          ]
        }
      ]
    }
  ],
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-12259"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/nltk/nltk"
    },
    {
      "type": "WEB",
      "url": "https://huntr.com/bounties/659ccf6d-12d4-4d4a-84c0-078633c35a5d"
    }
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-494"
    ],
    "severity": "MODERATE",
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-08-03T08:17:17Z"
  }
}