---
id: "GHSA-qvhx-rvgc-jhwf"
page: "https://infrastack.ai/live/GHSA-qvhx-rvgc-jhwf"
kind: "vulnerability"
aliases: ["GHSA-qvhx-rvgc-jhwf"]
title: "Duplicate Advisory: Quadratic-time CPU denial of service in ConllCorpusReader SRL instance builder via nested span rescan"
severity: "high"
cvss: 7.5
epss: null
exploited: false
status: "withdrawn"
category: "package"
products: [{"name": "nltk", "fixed": [], "affected": "< 3.10.4", "ecosystem": "pypi"}]
ecosystems: ["pypi"]
tags: ["cwe-400", "nlp", "nltk", "package", "python"]
not_affected_if: ["srl-reader-unused", "trusted-input-only"]
published_at: "2026-11-13T12:31:16+00:00"
first_seen_at: "2026-11-14T00:08:54+00:00"
updated_at: "2026-11-14T00:10:24+00:00"
sources: [{"source": "ghsa", "url": "https://github.com/advisories/GHSA-qvhx-rvgc-jhwf", "first_seen_at": "2026-11-14T00:08:54+00:00"}]
exploit_sources: []
---

# Duplicate Advisory: Quadratic-time CPU denial of service in ConllCorpusReader SRL instance builder via nested span rescan

Link for people: https://infrastack.ai/live/GHSA-qvhx-rvgc-jhwf (this .md is for agents)

NLTK before 3.10.4 has a quadratic-time flaw in the CoNLL SRL corpus reader, which runs when a corpus file is parsed. A crafted corpus with many predicates and span columns makes the process burn CPU for minutes, a denial of service.

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

## Affected

- pypi:nltk affected < 3.10.4 fixed no fixed version listed

## How to check

- Check the installed NLTK version with `pip show nltk`
- Look for `ConllCorpusReader` or `srl_instances` calls in code that parses CoNLL SRL files from untrusted input

## Fix

- `nltk` fixed in `3.10.4`
- This advisory is withdrawn as a duplicate of GHSA-v8f3-6phw-6mh9; check that advisory for the same fixed version

## Timeline

- 2026-11-14T00:08:54+00:00 ghsa https://github.com/advisories/GHSA-qvhx-rvgc-jhwf

## From the sources

## Duplicate Advisory

This advisory has been withdrawn because it is a duplicate of GHSA-v8f3-6phw-6mh9. This link is maintained to preserve external references.

## Original Description
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_