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Full vulnerability report · 2026
CVE-2026-33231High confidence

NLTK has unauthenticated remote shutdown in nltk.app.wordnet_app

nltk · nltk

7.5HighCVSS 3.1
Recommended action
Within 7 days

High technical severity with public exploit material referenced by a structured source; prioritise exposed affected systems while verifying vendor guidance.

Patch available
Distribution package intelligence

Ubuntu vendor package status

Canonical’s release and source-package findings are shown separately from local repository availability.

1 package state
Repository candidate not checked

A published vendor fix does not prove that a matching update is enabled and installable on a particular asset. Confirm the local package candidate before scheduling remediation.

Ubuntu releaseSource packageVendor stateFixed versionEvidence
Ubuntu 24.04 LTSnoble · esm-appsnltkVendor fix publishedCanonical reports that a fixed source package version has been published. Repository candidate availability is not checked by BlackTree.3.8.1-1ubuntu0.1~esm2Canonical record ↗Source updated 9 Sept 2026
Direct vendor intelligence

Authoritative vendor CSAF and VEX advisories

Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.

1 current
CVE-2026-33231 · CSAF 2.0 · revision 3 · finalRed Hat Product Securitynltk: NLTK: Denial of Service via unauthenticated remote shutdown
8 known affected

The vendor explicitly identifies these products as affected by this CVE.

  • lightspeed-core/lightspeed-stack-rhel9 as a component of Lightspeed Core
  • lightspeed-core/rag-tool-rhel9 as a component of Lightspeed Core
  • openshift-lightspeed/lightspeed-service-api-rhel9 as a component of OpenShift Lightspeed
  • ansible-automation-platform-24/de-supported-rhel8 as a component of Red Hat Ansible Automation Platform 2
  • ansible-automation-platform-25/de-minimal-rhel9 as a component of Red Hat Ansible Automation Platform 2
  • ansible-automation-platform-25/lightspeed-chatbot-rhel8 as a component of Red Hat Ansible Automation Platform 2
  • ansible-automation-platform-26/ee-minimal-rhel9 as a component of Red Hat Ansible Automation Platform 2
  • rhoai/odh-llama-stack-core-rhel9 as a component of Red Hat OpenShift AI (RHOAI)
Summary
A flaw was found in NLTK (Natural Language Toolkit), specifically in the `nltk.app.wordnet_app` component. An unauthenticated remote attacker can exploit this vulnerability by sending a specially crafted GET request to the local WordNet Browser HTTP server when it is running in its default configuration. This action causes the server process to terminate immediately, leading to a denial of service.
Remediation
For Red Hat OpenShift AI 2.25.7 see the following documentation, which will be updated shortly for this release, for important instructions on how to upgrade your cluster and fully apply this errata update: https://docs.redhat.com/en/documentation/red_hat_openshift_ai/
Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Select the national-authority views to include. The exact source language is shown on each matched advisory. Your choice is remembered on this device and encoded in the shareable URL.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2026-13885

No EUVD known-exploited evidence

NLTK (Natural Language Toolkit) is a suite of open source Python modules, data sets, and tutorials supporting research and development in Natural Language Processing. In versions 3.9.3 and prior, `nltk.app.wordnet_app` allows unauthenticated remote shutdown of the local WordNet Browser HTTP server when it is started in its default mode. A simple `GET /SHUTDOWN%20THE%20SERVER` request causes the process to terminate immediately via `os._exit(0)`, resulting in a denial of service. Commit bbaae83db86a0f49e00f5b0db44a7254c268de9b patches the issue.

EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
7.5 · CVSS 3.1
Advisory evidence
No linked advisory details stored yet
Recommended actionWithin 7 days

High technical severity with public exploit material referenced by a structured source; prioritise exposed affected systems while verifying vendor guidance.

Patch available
01

What, why and how

NLTK (Natural Language Toolkit) is a suite of open source Python modules, data sets, and tutorials supporting research and development in Natural Language Processing. In versions 3.9.3 and prior, `nltk.app.wordnet_app` allows unauthenticated remote shutdown of the local WordNet Browser HTTP server when it is started in its default mode. A simple `GET /SHUTDOWN%20THE%20SERVER` request causes the process to terminate immediately via `os._exit(0)`, resulting in a denial of service. Commit bbaae83db86a0f49e00f5b0db44a7254c268de9b patches the issue.

What

NLTK (Natural Language Toolkit) is a suite of open source Python modules, data sets, and tutorials supporting research and development in Natural Language Processing. In versions 3.9.3 and prior, `nltk.app.wordnet_app` allows unauthenticated remote shutdown of the local WordNet Browser HTTP server when it is started in its default mode. A simple `GET /SHUTDOWN%20THE%20SERVER` request causes the process to terminate immediately via `os._exit(0)`, resulting in a denial of service. Commit bbaae83db86a0f49e00f5b0db44a7254c268de9b patches the issue.

Why

A security-sensitive function is reachable without the authentication check that should protect it.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may disrupt the affected service.

What

NLTK (Natural Language Toolkit) is a suite of open source Python modules, data sets, and tutorials supporting research and development in Natural Language Processing. In versions 3.9.3 and prior, `nltk.app.wordnet_app` allows unauthenticated remote shutdown of the local WordNet Browser HTTP server when it is started in its default mode. A simple `GET /SHUTDOWN%20THE%20SERVER` request causes the process to terminate immediately via `os._exit(0)`, resulting in a denial of service. Commit bbaae83db86a0f49e00f5b0db44a7254c268de9b patches the issue.

Why

A security-sensitive function is reachable without the authentication check that should protect it.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may disrupt the affected service.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
Reference recorded

A structured CVE source labels at least one public reference as exploit material. BlackTree has not independently validated that it is safe, reliable or weaponised.

Likely attack path
a network path → Missing Authentication for Critical Function → disrupt the affected service
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
None
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Unchanged: impact remains within the vulnerable component's security authority
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-306 ↗

CWE-306: Missing Authentication for Critical Function. The product does not perform any authentication for functionality that requires a provable user identity or consumes a significant amount of resources.

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.

AVNetworkAttack vector: The vulnerable component can be reached over a network.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CNoneConfidentiality impact: No direct loss is represented by this metric.INoneIntegrity impact: No direct loss is represented by this metric.AHighAvailability impact: A successful attack can cause a major loss.
Post-exploitation / living off the land
No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
NetworkUnauthenticatedDenial of serviceCWE-306Public exploit reference
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

ENISA EUVD · EUVD-2026-13885Official EUVD mapping

NLTK (Natural Language Toolkit) is a suite of open source Python modules, data sets, and tutorials supporting research and development in Natural Language Processing. In versions 3.9.3 and prior, `nltk.app.wordnet_app` allows unauthenticated remote shutdown of the local WordNet Browser HTTP server when it is started in its default mode. A simple `GET /SHUTDOWN%20THE%20SERVER` request causes the process to terminate immediately via `os._exit(0)`, resulting in a denial of service. Commit bbaae83db86a0f49e00f5b0db44a7254c268de9b patches the issue.

Official EUVD record
BSI · German · WID-SEC-W-2026-0895IBM App Connect Enterprise: Mehrere Schwachstellen

Ein Angreifer kann mehrere Schwachstellen in IBM App Connect Enterprise ausnutzen, um Dateien zu manipulieren, um einen Denial of Service Angriff durchzuführen, um beliebigen Programmcode auszuführen, und um einen Cross-Site Scripting Angriff durchzuführen.

Official advisory
CERT-FR · French · CERTFR-2026-AVI-1094Multiples vulnérabilités dans les produits IBM

ord?id=CVE-2026-31411 Référence CVE CVE-2026-31419 https://www.cve.org/CVERecord?id=CVE-2026-31419 Référence CVE CVE-2026-31488 https://www.cve.org/CVERecord?id=CVE-2026-31488 Référence CVE CVE-2026-31692 https://www.cve.org/CVERecord?id=CVE-2026-31692 Référence CVE CVE-2026-31802 https://www.cve.org/CVERecord?id=CVE-2026-31802 Référence CVE CVE-2026-32286 https://www.cve.org/CVERecord?id=CVE-2026-32286 Référence CVE CVE-2026-3304 https://www.cve.org/CVERecord?id=CVE-2026-3304 Référence CVE CVE-2026-33227 https://www.cve.org/CVERecord?id=CVE-2026-33227 Référence CVE CVE-2026-33230 https://www.cve.org/CVERecord?id=CVE-2026-33230 Référence CVE CVE-2026-33231 https://www.cve.org/CVERecord?id=CVE-2026-33231 Référence CVE CVE-2026-33236 https://www.cve.org/CVERecord?id=CVE-2026-33236 Référence CVE CVE-2026-33416 https://www.cve.org/CVERecord?id=CVE-2026-33416 Référence CVE CVE-2026-33558 https://www.cve.org/CVERecord?id=CVE-2026-33558 Référence CVE CVE-2026-33671 https://www.cve.org/CVERecord?id=CVE-2026-33671 Référence CVE CVE-2026-33672 https://www.cve.org/CVERecord?id=CVE-2026-33672 Référence CVE CVE-2026-33750 https://www.cve.org/CVERecord?id=CVE-2026-33750 Référence CVE CVE-2026-33845 https://www.cve.org/CVERecord?id=CVE-2026-33845 Référence CVE CVE-2026-33846 https://www.cve.org/CVERecord?id=

Official advisory
CERT-FR · French · CERTFR-2026-AVI-0556Multiples vulnérabilités dans les produits VMware

ord?id=CVE-2026-32286 Référence CVE CVE-2026-32288 https://www.cve.org/CVERecord?id=CVE-2026-32288 Référence CVE CVE-2026-32289 https://www.cve.org/CVERecord?id=CVE-2026-32289 Référence CVE CVE-2026-32874 https://www.cve.org/CVERecord?id=CVE-2026-32874 Référence CVE CVE-2026-32875 https://www.cve.org/CVERecord?id=CVE-2026-32875 Référence CVE CVE-2026-3298 https://www.cve.org/CVERecord?id=CVE-2026-3298 Référence CVE CVE-2026-32990 https://www.cve.org/CVERecord?id=CVE-2026-32990 Référence CVE CVE-2026-33186 https://www.cve.org/CVERecord?id=CVE-2026-33186 Référence CVE CVE-2026-33230 https://www.cve.org/CVERecord?id=CVE-2026-33230 Référence CVE CVE-2026-33231 https://www.cve.org/CVERecord?id=CVE-2026-33231 Référence CVE CVE-2026-33236 https://www.cve.org/CVERecord?id=CVE-2026-33236 Référence CVE CVE-2026-33810 https://www.cve.org/CVERecord?id=CVE-2026-33810 Référence CVE CVE-2026-33816 https://www.cve.org/CVERecord?id=CVE-2026-33816 Référence CVE CVE-2026-33870 https://www.cve.org/CVERecord?id=CVE-2026-33870 Référence CVE CVE-2026-33871 https://www.cve.org/CVERecord?id=CVE-2026-33871 Référence CVE CVE-2026-34073 https://www.cve.org/CVERecord?id=CVE-2026-34073 Référence CVE CVE-2026-34267 https://www.cve.org/CVERecord?id=CVE-2026-34267 Référence CVE CVE-2026-34270 https://www.cve.org/CVERecord?id=

Official advisory
03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Patch available
Affected
lightspeed-core/lightspeed-stack-rhel9 as a component of Lightspeed Core; lightspeed-core/rag-tool-rhel9 as a component of Lightspeed Core; openshift-lightspeed/lightspeed-service-api-rhel9 as a component of OpenShift Lightspeed; ansible-automation-platform-24/de-supported-rhel8 as a component of Red Hat Ansible Automation Platform 2; ansible-automation-platform-25/de-minimal-rhel9 as a component of Red Hat Ansible Automation Platform 2; ansible-automation-platform-25/lightspeed-chatbot-rhel8 as a component of Red Hat Ansible Automation Platform 2; ansible-automation-platform-26/ee-minimal-rhel9 as a component of Red Hat Ansible Automation Platform 2; rhoai/odh-llama-stack-core-rhel9 as a component of Red Hat OpenShift AI (RHOAI)
Fixed
registry.redhat.io/rhoai/odh-pipeline-runtime-pytorch-llmcompressor-cuda-py312-rhel9@sha256:d34129a713ff030c034b5f927194119bd8f1996c1d84672f60d28171e048a294_amd64 as a component of Red Hat OpenShift AI 2.25; registry.redhat.io/rhoai/odh-ta-lmes-job-rhel9@sha256:12b22139069ac4f0679722c3020ae2ce5aa915d6aedd3837eb6a155e642acad0_ppc64le as a component of Red Hat OpenShift AI 2.25; registry.redhat.io/rhoai/odh-ta-lmes-job-rhel9@sha256:26d9256029f78df1b0d16a5d388d6caece5ad0c0639a76a99dbcc9f32c281002_amd64 as a component of Red Hat OpenShift AI 2.25; registry.redhat.io/rhoai/odh-ta-lmes-job-rhel9@sha256:429eee0ace6becaae1c63774098bce8df3c9e92a6d4bdc33cd2256dcec918025_arm64 as a component of Red Hat OpenShift AI 2.25; registry.redhat.io/rhoai/odh-ta-lmes-job-rhel9@sha256:ad7cc622e887ceffb195db5188e224a8c4bb1b52711eec195edadba77673c93f_s390x as a component of Red Hat OpenShift AI 2.25; registry.redhat.io/rhoai/odh-workbench-jupyter-pytorch-llmcompressor-cuda-py312-rhel9@sha256:2b8600182a04936b9c479c585c4e95d72574cbdfe3bea0571b4620db66865004_amd64 as a component of Red Hat OpenShift AI 2.25; registry.redhat.io/rhoai/odh-pipeline-runtime-pytorch-llmcompressor-cuda-py312-rhel9@sha256:159a74b15af89406e047216268997c2a4e828e75c146c8ee66419c6e0651b08d_amd64 as a component of Red Hat OpenShift AI 3.3; registry.redhat.io/rhoai/odh-trustyai-nemo-guardrails-server-rhel9@sha256:1bd8ef0344f81b51c980bd013c566c25641da1b1005e2a72161389d4aef589e8_amd64 as a component of Red Hat OpenShift AI 3.3; registry.redhat.io/rhoai/odh-trustyai-nemo-guardrails-server-rhel9@sha256:4cedbca17d308dc47345d65a582159e1f31febf2c419ee264229724b4ce92c4e_arm64 as a component of Red Hat OpenShift AI 3.3; registry.redhat.io/rhoai/odh-workbench-jupyter-pytorch-llmcompressor-cuda-py312-rhel9@sha256:25523480cba8eb7db0062e87ce3068e4a04c47fc448de852fc3e43cb4d0742e1_amd64 as a component of Red Hat OpenShift AI 3.3
Action
For Red Hat OpenShift AI 2.25.7 see the following documentation, which will be updated shortly for this release, for important instructions on how to upgrade your cluster and fully apply this errata update: https://docs.redhat.com/en/documentation/red_hat_openshift_ai/
Workaround
No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
04

Evidence and provenance

Published 20 Mar 2026 · Last source change 9 Sept 2026, 12:04 UTC · CWE-306 · Missing Authentication for Critical Function

CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2026-13885
Product sourceVendor CSAF · Red Hat Product Security
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceCNA
NVD statusNVD modified after enrichment

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates →
  1. Vendor guidanceAuthoritative vendor guidance changed from authoritative remediation link · patch, vendor advisory to authoritative remediation link · patch, vendor advisory.
    Before
    authoritative remediation link · patch, vendor advisory
    After
    authoritative remediation link · patch, vendor advisory
    security-advisories@github.com ↗
  2. Vendor guidanceAuthoritative vendor guidance changed from authoritative remediation link · patch, vendor advisory to authoritative remediation link · patch, vendor advisory.
    Before
    authoritative remediation link · patch, vendor advisory
    After
    authoritative remediation link · patch, vendor advisory
    security-advisories@github.com ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Fixed release or patch reference recorded
ENISA EUVD · EUVD-2026-13885↗Vendor CSAF · Red Hat Product Security↗CISA Vulnrichment SSVC evidence↗Public exploit reference↗Patch or update reference↗Official CVE record (CNA and ADP data)↗NVD record↗
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
Free version - for non-commercial use only.CVE-2026-33231 · cve.blacktree.nl