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CVE-2026-70626 medium CVSS 6.2

Vulnerability in nltk (CVE-2026-70626)

Summary

Vulnerability in nltk (CVE-2026-70626). Confidential information can be exposed externally. Exploitable via CorpusReader. Mitigation: upgrade to 3.9.4 or later.

Original description

The description as published by the source.

Summary

nltk.corpus.reader.api.CorpusReader.open() can be used to read files outside the intended corpus root via a symlink placed inside that root. Although NLTK blocks absolute paths and .. traversal, the current boundary check is only lexical and does not account for symlink resolution. This leads to an arbitrary local file read / filesystem sandbox bypass for applications that rely on CorpusReader or FileSystemPathPointer to restrict file access.

Details

The vulnerable flow is:

  • nltk/corpus/reader/api.py:222

    • CorpusReader.open() blocks absolute paths and .., then calls self._root.join(file).open()

  • nltk/data.py:398

    • FileSystemPathPointer.join() joins the requested file ID and checks whether the resulting path still appears to remain under the configured root

The problem is that the check is based on the lexical path after os.path.normpath(), not on the resolved path after following symlinks.

Current behavior:

  1. CorpusReader.open() rejects:
    • absolute paths
    • .. path traversal
  2. FileSystemPathPointer.join() computes:
    • joined = os.path.normpath(os.path.join(self._path, fileid))
    • root = os.path.normpath(self._path)
  3. It allows the access if joined starts with root

This misses the case where a path stays inside the root lexically, but resolves outside the root via a symlink already presen…

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-2026-70626 has been found in nltk.
Attackers can target a specific entry point like CorpusReader over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 6.2/10.
What to do: upgrade nltk to 3.9.4 or later.
If unsure, ask your IT team or search "nltk CVE-2026-70626" on the vendor's site.

CVE-2026-70626 (nltk) — CWE-59 / CVSS v3 6.2
Attack vector: local / unauthenticated / no user interaction
Attack surface: CorpusReader / FileSystemPathPointer / joined / root
Patched: 3.9.4 — 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

A vulnerability (CWE-59) exists in nltk. Attackers reach the vulnerable code path via CorpusReader without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of nltk. Attack surface: CorpusReader / FileSystemPathPointer / joined / root.

🔥 Severity

Severity: Medium (CVSS 6.2/10). Confidential information can be exposed externally.

🔧 How to fix

Update to 3.9.4.

🛡️ 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 3.9.4

    ステージング環境で 3.9.4 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":"3.9.4"}]}]
PyPI nltk
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.9.4"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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