Vulnerability in nltk (CVE-2026-65915)
Summary
Vulnerability in nltk (CVE-2026-65915). Confidential information can be exposed externally. Exploitable via False. Mitigation: upgrade to 3.10.0 or later.
Original description
The description as published by the source.
Summary
There's a logic bug in FileSystemPathPointer.open() inside nltk/data.py
that makes the sandbox check permanently inert. The guard condition is always
False — meaning any file the process can read is accessible by passing a
file:// URL to nltk.data.load().
Details
In nltk/data.py, FileSystemPathPointer.open() was patched at some point
with a comment saying "SECURITY PATCH ENFORCING SANDBOX", but the check
doesn't work:
def open(self, encoding=None):
path = os.path.normpath(self._path)
# Block raw absolute reads such as "/" "C:\\Windows" etc.
if os.path.isabs(path) and path != os.path.normpath(self._path):
raise ValueError(f"Direct absolute file access blocked: {path}")
stream = open(self._path, "rb")
path is set to os.path.normpath(self._path) on line 1, then compared
against os.path.normpath(self._path) again in the condition. They are
always equal. The ValueError never fires.
On top of that, __init__ already calls os.path.abspath() before storing
self._path, so it's normalized before open() is even called. Running
normpath on it again changes nothing.
The stream = open(self._path, "rb") line is always reached regardless of
what path was passed in.
PoC
Tested on Python 3.11, NLTK 3.9.1, Ubuntu 22.04.
import nltk
from nltk.data import FileSystemPathPointer
# direct construction
ptr = FileSystemPathPointer("/etc/passwd")
with ptr.open() as f:
print(f.re…
Source: GitHub Security Advisories (Global) NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-65915 has been found in nltk.
Attackers can target a specific entry point like False over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 6.5/10.
What to do: upgrade nltk to 3.10.0 or later.
If unsure, ask your IT team or search "nltk CVE-2026-65915" on the vendor's site.
CVE-2026-65915 (nltk) — CWE-284 / CVSS v3 6.5
Attack vector: remote (network-reachable) / no user interaction
Attack surface: False / path / ValueError / __init__
Patched: 3.10.0 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-284) exists in nltk. Attackers reach the vulnerable code path via False.
Check the vendor advisory for the affected versions of nltk. Attack surface: False / path / ValueError / __init__.
Severity: Medium (CVSS 6.5/10). Confidential information can be exposed externally.
Update to 3.10.0.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'nltk' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'nltk' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
nltkを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade nltk to 3.10.0ステージング環境で 3.10.0 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
- advisory disclosure@vulncheck.com
- exploit github.com
- web nvd.nist.gov
- web github.com
- web github.com
- web github.com
- web github.com
- web huntr.com
- web github.com