CVE-2026-81724

MEDIUMPre-NVD 5.35.3—
EchelonGraph scoreHIGH confidence

Score 5.3 from GitHub Security Advisory published 2026-08-27. a secondary CVSS source baseline 5.3; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, secondary
5.3EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 5.3Exploit: None knownExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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.

CVSS v3
5.3
EG Score
5.3(high)
EG Risk
28(Track)
EG Risk 28/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity53% × 45%
Exploitation0% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
19%
KEV
Not listed

Published

August 27, 2026

Last Modified

August 31, 2026

Advisory Details (2)

Auto-updated Aug 27, 2026
🔬 Proof of concept available. Patch available. Sources: github.
generic

NLTK before 3.10.3 Denial of Service via Uncontrolled Recursion | Advisories | VulnCheck

https://www.vulncheck.com/advisories/nltk-before-3.10.3-denial-of-service-via-uncontrolled-recursion
github Patch Available🟡 PoC Available

Uncontrolled recursion in nltk.featstruct.FeatStructReader causes unhandled RecursionError (DoS) via deeply nested feature-structure input · Advisory · nltk/nltk · GitHub

https://github.com/nltk/nltk/security/advisories/GHSA-cw6x-m8jw-qmrh

Vendor Advisories for CVE-2026-81724(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Affected Packages

(4 across 4 ecosystems)
Debian:12(1)
PackageVulnerable rangeFixed inDependents
nltk3.10.0-1 ... 3.9.3-1 (9 versions)——
Debian:13(1)
PackageVulnerable rangeFixed inDependents
nltk3.10.0-1 ... 3.9.3-1 (6 versions)——
Debian:14(1)
PackageVulnerable rangeFixed inDependents
nltk3.10.0-1, 3.10.1-1, 3.9.1-2, 3.9.2-1, 3.9.3-13.10.3-1—
PyPI(1)
PackageVulnerable rangeFixed inDependents
nltk0.8 ... 3.9b1 (68 versions)3.10.3—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 11× in last 7d / 48× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-09-18 21:29 UTCEG score recompute
  2. 2026-09-18 19:28 UTCEPSS rescore
  3. 2026-09-17 21:00 UTCEG score recompute
  4. 2026-09-16 21:30 UTCEG score recompute
  5. 2026-09-16 14:08 UTCEPSS rescore
  6. 2026-09-16 05:15 UTCEPSS rescore
  7. 2026-09-15 21:35 UTCEG score recompute
  8. 2026-09-15 03:12 UTCEPSS rescore
  9. 2026-09-15 03:12 UTCEPSS rescore
  10. 2026-09-13 22:30 UTCEG score recompute
  11. 2026-09-12 23:01 UTCEG score recompute
  12. 2026-09-11 23:31 UTCEG score recompute
  13. 2026-09-11 14:53 UTCEPSS rescore
  14. 2026-09-11 14:53 UTCEPSS rescore
  15. 2026-09-11 00:01 UTCEG score recompute
  16. 2026-09-09 00:40 UTCEG score recompute
  17. 2026-09-08 22:01 UTCEPSS rescore
  18. 2026-09-07 17:58 UTCEG score recompute
  19. 2026-09-06 18:29 UTCEG score recompute
  20. 2026-09-06 13:48 UTCEPSS rescore
  21. 2026-09-05 19:00 UTCEG score recompute
  22. 2026-09-05 15:31 UTCEPSS rescore
  23. 2026-09-04 19:30 UTCEG score recompute
  24. 2026-09-04 05:07 UTCEPSS rescore
  25. 2026-09-02 20:29 UTCEG score recompute
Show 23 more
  1. 2026-09-02 14:12 UTCEPSS rescore
  2. 2026-09-01 18:47 UTCEG score recompute
  3. 2026-09-01 18:46 UTCGHSA enrichment
  4. 2026-09-01 13:54 UTCEPSS rescore
  5. 2026-09-01 04:40 UTCEPSS rescore
  6. 2026-09-01 04:40 UTCEPSS rescore
  7. 2026-08-31 19:14 UTCGHSA enrichment
  8. 2026-08-31 17:35 UTCEG score recompute
  9. 2026-08-31 17:34 UTCGHSA enrichment
  10. 2026-08-30 19:18 UTCEPSS rescore
  11. 2026-08-30 19:17 UTCEPSS rescore
  12. 2026-08-30 18:05 UTCEG score recompute
  13. 2026-08-30 18:05 UTCGHSA enrichment
  14. 2026-08-30 01:22 UTCEPSS rescore
  15. 2026-08-29 18:36 UTCEG score recompute
  16. 2026-08-29 18:35 UTCGHSA enrichment
  17. 2026-08-28 21:42 UTCEPSS rescore
  18. 2026-08-28 19:03 UTCGHSA enrichment
  19. 2026-08-27 20:27 UTCEG score recompute
  20. 2026-08-27 20:27 UTCGHSA enrichment
  21. 2026-08-27 17:24 UTCEG score recompute
  22. 2026-08-27 16:47 UTCEG score recompute
  23. 2026-08-27 16:43 UTCMITRE cvelistV5first tracked

Frequently asked(5)

What is CVE-2026-81724?
CVE-2026-81724 is a medium vulnerability published on August 27, 2026. 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…
When was CVE-2026-81724 disclosed?
CVE-2026-81724 was first published in the National Vulnerability Database on August 27, 2026, with the most recent update on August 31, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-81724 actively exploited?
CVE-2026-81724 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 80.9% of all scored CVEs.
What is the CVSS score of CVE-2026-81724?
CVE-2026-81724 has a CVSS v3 base score of 5.3 (NVD).
How do I remediate CVE-2026-81724?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-81724, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

See which npm, PyPI, Go, and Maven packages are affected by CVE-2026-81724

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