---
id: CVE-2026-80206
title: 'nltk: NLTK: Denial of Service vulnerability in tgrep module (CVE-2026-80206)'
summary: >-
  A flaw was found in NLTK, specifically within its tgrep module. This
  vulnerability, known as Regular Expression Denial of Service (ReDoS), allows a
  remote attacker to provide specially crafted regular expressions. When
  processed, these exp…
severity: medium
cvss: 5.9
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H'
cvssSource: vendor
cwe: CWE-1333
vendor: Red Hat
product: Red Hat OpenShift AI (RHOAI)
affected:
  - exploit_intelligence
  - lightspeed_core
  - openshift_lightspeed
  - ansible_automation_platform 2
  - openshift_ai_rhoai
patched:
  - nltk 3.10.3
published: '2026-08-26'
updated: '2026-10-15'
sourceUpdated: '2026-10-15T11:23:06+00:00'
source: CSAF
sourceUrl: 'https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-80206.json'
references:
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-80206.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-80206'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2524336'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-80206'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-80206'
  - url: 'https://github.com/nltk/nltk/security/advisories/GHSA-w3v8-gmh9-3wv7'
  - url: >-
      https://www.vulncheck.com/advisories/nltk-3.10.2-regular-expression-denial-of-service-via-tgrep
  - url: >-
      https://github.com/nltk/nltk/commit/0072ea2fb8be22e038a36e887b7061bb6b9339d9
  - url: 'https://github.com/nltk/nltk'
  - url: 'https://github.com/nltk/nltk/releases/tag/v3.10.3'
  - url: >-
      https://github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2026-3751.yaml
  - url: 'https://github.com/advisories/GHSA-w3v8-gmh9-3wv7'
tags:
  - csaf
  - vex
  - red-hat
  - osv
  - pip
  - ghsa
epss: 0.0044
epssPercentile: 0.38089
aliases:
  - GHSA-w3v8-gmh9-3wv7
  - PYSEC-2026-3751
ecosystem: pip
ingestedAt: '2026-09-02T19:31:25.120Z'
---

## Overview

A flaw was found in NLTK, specifically within its tgrep module. This vulnerability, known as Regular Expression Denial of Service (ReDoS), allows a remote attacker to provide specially crafted regular expressions. When processed, these expressions can cause indefinite CPU saturation, leading to a complete denial of service for the Python process utilizing the NLTK library.

## Vendor advisories

- **Red Hat VEX** · Moderate · affected: Exploit Intelligence, Lightspeed Core, OpenShift Lightspeed, Red Hat Ansible Automation Platform 2, Red Hat OpenShift AI (RHOAI) · no fix planned: Exploit Intelligence, Red Hat Ansible Automation Platform 2, Lightspeed Core, OpenShift Lightspeed, … · updated 2026-10-15 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-80206.json)

**nltk: NLTK: Denial of Service vulnerability in tgrep module** — rated Moderate by Red Hat. Released 2026-08-26, updated 2026-10-15.

Affected:

- Exploit Intelligence
- Lightspeed Core
- OpenShift Lightspeed
- Red Hat Ansible Automation Platform 2
- Red Hat OpenShift AI (RHOAI)

No fix planned:

- Exploit Intelligence
- Red Hat Ansible Automation Platform 2
- Lightspeed Core
- OpenShift Lightspeed
- Red Hat OpenShift AI (RHOAI)

## Remediation

Out of support scope

Workarounds / mitigations:

- Sanitize or restrict external input passed to NLTK's tgrep compilation functions to prevent execution of untrusted regular expressions, or enforce application-level timeouts using process isolation/multiprocessing wrappers to restrict CPU consumption.

## Package advisory (CVE-2026-80206)

Affected packages:

- `nltk < 3.10.3`

Patched in:

- `nltk 3.10.3`

Source: https://osv.dev/vulnerability/GHSA-w3v8-gmh9-3wv7