Vulnerability in nltk (CVE-2026-12259)
Summary
Vulnerability in nltk (CVE-2026-12259). Data can be tampered with by attackers. Mitigation: upgrade to 3.9.3 or later.
Original description
The description as published by the source.
In nltk version 3.9.4, the nltk.downloader.Downloader._download_package() function writes downloaded package bytes to disk and may extract them before enforcing SHA-256 or MD5 checksum validation. This allows an attacker to tamper with the package response body for info.url through a compromised mirror, malicious proxy, or other source-substitution condition, leading to the installation of attacker-controlled package bytes. The vulnerability can result in malicious corpus or model content being trusted by downstream users or applications.
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-2026-12259 has been found in nltk.
Data can be tampered with by attackers. CVSS score: 6.5/10.
What to do: upgrade nltk to 3.9.3 or later.
If unsure, ask your IT team or search "nltk CVE-2026-12259" on the vendor's site.
CVE-2026-12259 (nltk) — CWE-494 / CVSS v3 6.5
Attack vector: remote (network-reachable) / unauthenticated
Patched: 3.9.3 — 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.
A vulnerability (CWE-494) exists in nltk.
Check the vendor advisory for the affected versions of nltk.
Severity: Medium (CVSS 6.5/10). Data can be tampered with by attackers.
Update to 3.9.3.
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
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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 3.9.3ステージング環境で 3.9.3 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。
-
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
Fix status by distribution
Fixed packages published by each distribution for this CVE
- Debian DEBIAN-CVE-2026-12259 nltk
- Ubuntu UBUNTU-CVE-2026-12259 nltk
References
- advisory nvd.nist.gov
- advisory vulncheck.com
- advisory github.com
- advisory nvd.nist.gov
- package github.com
- report huntr.com
- report github.com
- web github.com
- web github.com
- web github.com
- web github.com
- web github.com