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CVE-2026-79676 medium CVSS 5.9

Path Traversal in nltk (CVE-2026-79676)

Summary

Path traversal in nltk (CVE-2026-79676). Confidential information can be exposed externally. Exploitable via nltk.corpus.reader.ipipan. Mitigation: upgrade to 3.10.3 or later.

Original description

The description as published by the source.

Summary

Several corpus readers still step outside NLTK's symlink-aware trusted-root model. They derive in-root paths from trusted corpus state, convert those paths back into plain strings, and reopen them with built-in open() rather than nltk.pathsec.open().

Details

  • Vulnerability type: Path traversal and symlink boundary bypass
  • Affected component: nltk.corpus.reader.ipipan, nltk.corpus.reader.crubadan, nltk.corpus.reader.lin
  • Affected versions: Published 3.9.4 and current source v3.10.0-rc2 both reproduced.
  • Patched versions: Not yet patched
  • Root cause: Root-derived paths are reopened with raw open() without preserving the trusted-root boundary.

IPIPANCorpusReader opens header.xml derived from morph.xml, CrubadanCorpusReader opens table.txt directly, and LinThesaurusCorpusReader opens simN.lsp paths returned from its own root helpers. Under pathsec.ENFORCE=True, a symlink placed inside the trusted corpus root can point outside the root and still be parsed successfully. It was confirmed parsed outside-root content is returned through public methods such as channels(), domains(), categories(), langs(), crubadan_to_iso(), synonyms(), and scored_synonyms().

PoC

Preconditions

  • The application processes attacker-influenced corpora inside a trusted NLTK data root or trusted corpus directory.

Steps

  1. Create a trusted corpus root and keep pathsec.ENFORCE=True with that root allowli…

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-2026-79676 has been found in nltk.
Attackers can target a specific entry point like nltk.corpus.reader.ipipan over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 5.9/10.
What to do: upgrade nltk to 3.10.3 or later.
If unsure, ask your IT team or search "nltk CVE-2026-79676" on the vendor's site.

CVE-2026-79676 (nltk) — CWE-22 / CVSS v3 5.9
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: nltk.corpus.reader.ipipan / nltk.corpus.reader.crubadan / nltk.corpus.reader.lin / IPIPANCorpusReader
Patched: 3.10.3 — 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 nltk.corpus.reader.ipipan without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of nltk. Attack surface: nltk.corpus.reader.ipipan / nltk.corpus.reader.crubadan / nltk.corpus.reader.lin / IPIPANCorpusReader.

🔥 Severity

Severity: Medium (CVSS 5.9/10). Confidential information can be exposed externally.

🔧 How to fix

Update to 3.10.3.

🛡️ 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 3.10.3

    ステージング環境で 3.10.3 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":"3.10.3"}]}]
PyPI nltk
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.10.3"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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