CVE-2026-33231Public exploitNetwork attack vector

Unauthenticated service shutdown via exposed HTTP route

Published Mar 20, 2026 · Updated Mar 20, 2026

Denial of service in NLTK 3.9.3 and earlier allows remote attackers to terminate the WordNet Browser HTTP server with one GET request. The nltk.app.wordnet_app handler URL-decodes the request path and calls os._exit(0) when it equals SHUTDOWN THE SERVER, without authentication. The server must be running in its default browser mode on a port reachable by the attacker; the consequence is an immediate service shutdown.

CVSS severity7.5
High
EPSS probability1.21%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in NLTK 3.9.3 and earlier allows remote attackers to terminate the WordNet Browser HTTP server with one GET request. The nltk.app.wordnet_app handler URL-decodes the request path and calls os._exit(0) when it equals SHUTDOWN THE SERVER, without authentication. The server must be running in its default browser mode on a port reachable by the attacker; the consequence is an immediate service shutdown.

The record

CVE
CVE-2026-33231
Published
Mar 20, 2026
Updated
Mar 20, 2026
Vendor
NLTK Project
Product
NLTK
Classifications
CWE-306, T1489
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 20, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 20, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=<= 3.9.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

NLTK Project · NLTKversion=<= 3.9.3

Published CVSS scores

7.5redhat-SADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
7.5GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-306Missing Authentication for Critical Function
T1489Service Stop

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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