{
  "affected": [
    {
      "ranges": [
        {
          "database_specific": {
            "extracted_events": [
              {
                "introduced": "0"
              },
              {
                "fixed": "3.10.3"
              }
            ],
            "source": [
              "AFFECTED_FIELD",
              "DESCRIPTION"
            ]
          },
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "303f6e2ba8e4548a5f54fd65d86bb5c9a949f1db"
            }
          ],
          "repo": "https://github.com/nltk/nltk",
          "type": "GIT"
        }
      ]
    }
  ],
  "aliases": [
    "GHSA-f794-5jv7-7672"
  ],
  "database_specific": {
    "cna_assigner": "VulnCheck",
    "cwe_ids": [
      "CWE-59"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/81xxx/CVE-2026-81727.json"
  },
  "details": "NLTK versions before 3.10.3 contain a filesystem containment bypass vulnerability in the Downloader.download and Downloader.incr_download methods that allows attackers to overwrite files outside the install root through pre-existing hardlinks. Attackers with write access to a shared downloader directory can create hardlinks pointing to outside-root files that are then overwritten during normal package extraction, mutating files outside the intended install tree.",
  "id": "CVE-2026-81727",
  "modified": "2026-08-30T03:30:44.428292407Z",
  "published": "2026-08-27T14:51:19.564Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/81xxx/CVE-2026-81727.json"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/nltk/nltk/security/advisories/GHSA-f794-5jv7-7672"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-81727"
    },
    {
      "type": "ADVISORY",
      "url": "https://www.vulncheck.com/advisories/nltk-before-3.10.3-hardlink-file-overwrite-via-downloader"
    }
  ],
  "schema_version": "1.9.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:H/VA:H/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "NLTK before 3.10.3 Hardlink File Overwrite via downloader"
}