---
id: "CVE-2026-126297"
page: "https://infrastack.ai/live/CVE-2026-126297"
kind: "vulnerability"
aliases: ["CVE-2026-126297"]
title: "NLTK: crafted CoNLL corpus file pins CPU for minutes"
severity: "high"
cvss: 8.7
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["nltk", "package", "python"]
not_affected_if: ["no-untrusted-corpus-input", "reader-not-used"]
published_at: "2026-11-13T10:17:34+00:00"
first_seen_at: "2026-11-13T10:47:14+00:00"
updated_at: "2026-11-13T10:50:31+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-126297", "first_seen_at": "2026-11-13T10:47:14+00:00"}]
exploit_sources: []
---

# NLTK: crafted CoNLL corpus file pins CPU for minutes

Link for people: https://infrastack.ai/live/CVE-2026-126297 (this .md is for agents)

NLTK before 3.10.4 has a quadratic-time flaw in ConllCorpusReader._get_srl_instances that re-scans spans in nested loops. A crafted CoNLL SRL corpus with many predicates and span columns can exhaust CPU and pin a core for minutes.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the installed NLTK version with `pip show nltk` or `python -c "import nltk; print(nltk.__version__)"`
- Look for code that calls ConllCorpusReader on corpus files that come from outside the team

## Fix

- NLTK: `3.10.4` or later (per the NVD description: before 3.10.4 is affected)

## Timeline

- 2026-11-13T10:47:14+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-126297

## Documents

- [advisory] Vendor advisory: github.com https://github.com/nltk/nltk/security/advisories/GHSA-v8f3-6phw-6mh9
- [advisory] Third-party advisory: www.vulncheck.com https://www.vulncheck.com/advisories/nltk-before-3.10.4-cpu-denial-of-service-via-conllcorpusreader-srl-instances

## From the sources

NLTK before 3.10.4 contains a quadratic-time denial of service vulnerability in ConllCorpusReader._get_srl_instances that allows remote attackers to exhaust CPU through nested span rescans. Attackers can supply a crafted CoNLL SRL corpus with many predicates and span columns, placing the head span last, to pin a core for minutes.

---

_Free to read, with fair use of about 60 pages a minute. For higher limits or API access: sales@infrastack.ai_