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CVE-2026-63312 high CVSS 7.5

Path Traversal in nltk (CVE-2026-63312)

Summary

Path traversal in nltk (CVE-2026-63312). Confidential information can be exposed externally. Exploitable via PermissionError. Mitigation: upgrade to 3.10.0 or later.

Original description

The description as published by the source.

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…

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-2026-63312 has been found in nltk.
Attackers can target a specific entry point like PermissionError over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 7.5/10.
What to do: upgrade nltk to 3.10.0 or later.
If unsure, ask your IT team or search "nltk CVE-2026-63312" on the vendor's site.

CVE-2026-63312 (nltk) — CWE-22 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: PermissionError / StreamBackedCorpusView / fileid / ENFORCE
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.

❓ What is the problem

Path traversal (CWE-22) exists in nltk. Attackers reach the vulnerable code path via PermissionError without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of nltk. Attack surface: PermissionError / StreamBackedCorpusView / fileid / ENFORCE.

🔥 Severity

Severity: High (CVSS 7.5/10). Confidential information can be exposed externally.

🔧 How to fix

Update to 3.10.0.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

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

  1. 1
    Identify 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。

  2. 2
    Apply 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。

  3. 3
    Post-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

pip nltk
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.10.0"}]}]
PyPI nltk
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.10.0"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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