Vulnerability in nltk (CVE-2026-81725)
Summary
Vulnerability in nltk (CVE-2026-81725). Risk of unauthorized operations or information disclosure. Exploitable via Pl196xCorpusReader. Mitigation: upgrade to 3.10.3 or later.
Original description
The description as published by the source.
NLTK before 3.10.3 contains a regular expression denial of service vulnerability in Pl196xCorpusReader that allows attackers to cause quadratic CPU consumption by supplying malformed TEI blocks with many unmatched opening tags. Attackers can exploit lazy regex patterns in the read_block method through public APIs like words() and tagged_words() to force repeated rescans and achieve near-quadratic runtime growth.
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-2026-81725 has been found in nltk.
Attackers can target a specific entry point like Pl196xCorpusReader over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 3.7/10.
What to do: upgrade nltk to 3.10.3 or later.
If unsure, ask your IT team or search "nltk CVE-2026-81725" on the vendor's site.
CVE-2026-81725 (nltk) — CWE-400 / CVSS v3 3.7
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: Pl196xCorpusReader
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-400) exists in nltk. Attackers reach the vulnerable code path via Pl196xCorpusReader without authentication.
Check the vendor advisory for the affected versions of nltk. Attack surface: Pl196xCorpusReader.
Severity: Low (CVSS 3.7/10). Risk of unauthorized operations or information disclosure.
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-2026-81725 nltk
- Ubuntu UBUNTU-CVE-2026-81725 nltk
References
- advisory github.com
- advisory vulncheck.com
- advisory nvd.nist.gov
- advisory github.com
- package github.com
- web github.com
- web github.com
- web github.com
- web github.com
- web github.com