Vulnerability in nltk (CVE-2026-81724)
Summary
Vulnerability in nltk (CVE-2026-81724). Risk of unauthorized operations or information disclosure. Exploitable via nltk.featstruct.FeatStructReader. Mitigation: upgrade to 3.10.3 or later.
Original description
The description as published by the source.
NLTK before 3.10.3 contains an uncontrolled recursion vulnerability in nltk.featstruct.FeatStructReader that allows unauthenticated attackers to cause a denial of service by supplying deeply nested feature-structure input. Attackers can craft trivial payloads with nested brackets that exceed Python's recursion limit and raise an unhandled RecursionError, crashing applications that parse user-supplied feature structures or feature grammars.
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-2026-81724 has been found in nltk.
Attackers can target a specific entry point like nltk.featstruct.FeatStructReader over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 5.3/10.
What to do: upgrade nltk to 3.10.3 or later.
If unsure, ask your IT team or search "nltk CVE-2026-81724" on the vendor's site.
CVE-2026-81724 (nltk) — CWE-674 / CVSS v3 5.3
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: nltk.featstruct.FeatStructReader / RecursionError / ValueError / LogicalExpressionException
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-674) exists in nltk. Attackers reach the vulnerable code path via nltk.featstruct.FeatStructReader without authentication.
Check the vendor advisory for the affected versions of nltk. Attack surface: nltk.featstruct.FeatStructReader / RecursionError / ValueError / LogicalExpressionException.
Severity: Medium (CVSS 5.3/10). 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
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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 3.10.3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-2026-81724 nltk
- Ubuntu UBUNTU-CVE-2026-81724 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