Vulnerability in nltk (DEBIAN-CVE-2026-12243)

Summary

Vulnerability in nltk (DEBIAN-CVE-2026-12243). Confidential information can be exposed externally. Exploitable via _UNSAFE_NO_PROTOCOL_RE.

Original description

The description as published by the source.

NLTK version 3.9.4 is vulnerable to a path traversal attack due to an incomplete fix for GitHub Issue #3504. The _UNSAFE_NO_PROTOCOL_RE regex in nltk/data.py checks for literal ../ sequences but fails to account for percent-encoded traversal sequences such as ..%2f. The url2pathname() function decodes these sequences after the validation step, allowing an attacker to bypass the protection. This vulnerability enables an attacker to read arbitrary files accessible to the Python process by controlling the resource name parameter passed to nltk.data.load() or nltk.data.find(). The issue affects applications that rely on NLTK for resource loading, including NLP web applications, Jupyter notebooks, and CLI tools. The default pathsec.ENFORCE=False setting exacerbates the impact by not blocking the file read at the open() stage.

Source: OSV.dev (Open Source Vulnerabilities) OSV

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 DEBIAN-CVE-2026-12243 has been found in nltk.
Attackers can target a specific entry point like _UNSAFE_NO_PROTOCOL_RE over the network to misuse the product.
Confidential information can be exposed externally.
What to do: apply the vendor's official patched release.
If unsure, ask your IT team or search "nltk DEBIAN-CVE-2026-12243" on the vendor's site.

DEBIAN-CVE-2026-12243 (nltk)
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: _UNSAFE_NO_PROTOCOL_RE
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 (unclassified) exists in nltk. Attackers reach the vulnerable code path via _UNSAFE_NO_PROTOCOL_RE without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of nltk. Attack surface: _UNSAFE_NO_PROTOCOL_RE.

🔥 Severity

Severity: ?. Confidential information can be exposed externally.

🔧 How to fix

Update to the patched release per vendor advisory.

🛡️ 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
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
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

Debian:11 nltk

[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}]

Debian:12 nltk

[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}]

Debian:13 nltk

[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}]

Debian:14 nltk

[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}]

References

advisory security-tracker.debian.org