Vulnerability in nltk (CVE-2026-81727)
Summary
Vulnerability in nltk (CVE-2026-81727). Data can be tampered with by attackers. Exploitable via nltk.downloader.Downloader.download. Mitigation: upgrade to 3.10.3 or later.
Original description
The description as published by the source.
NLTK versions before 3.10.3 contain a filesystem containment bypass vulnerability in the Downloader.download and Downloader.incr_download methods that allows attackers to overwrite files outside the install root through pre-existing hardlinks. Attackers with write access to a shared downloader directory can create hardlinks pointing to outside-root files that are then overwritten during normal package extraction, mutating files outside the intended install tree.
Source: NIST National Vulnerability Database 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-2026-81727 has been found in nltk.
Attackers can target a specific entry point like nltk.downloader.Downloader.download over the network to misuse the product.
Data can be tampered with by attackers. CVSS score: 7.1/10.
What to do: upgrade nltk to 3.10.3 or later.
If unsure, ask your IT team or search "nltk CVE-2026-81727" on the vendor's site.
CVE-2026-81727 (nltk) — CWE-59 / CVSS v3 7.1
Attack vector: local / no user interaction
Attack surface: nltk.downloader.Downloader.download / nltk.downloader.Downloader.incr_download
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.
A vulnerability (CWE-59) exists in nltk. Attackers reach the vulnerable code path via nltk.downloader.Downloader.download.
Check the vendor advisory for the affected versions of nltk. Attack surface: nltk.downloader.Downloader.download / nltk.downloader.Downloader.incr_download.
Severity: High (CVSS 7.1/10). Data can be tampered with by attackers.
Update to 3.10.3.
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
-
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 3.10.3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。
-
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-2026-81727 nltk
- Ubuntu UBUNTU-CVE-2026-81727 nltk
References
- advisory github.com
- advisory vulncheck.com
- advisory nvd.nist.gov
- advisory github.com
- web github.com
- web github.com
- web github.com
- web github.com
- web github.com
- web github.com