How severe is CVE-2026-33231?

CVE-2026-33231 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2026-33231 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (54th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-33231?

CVE-2026-33231 affects Nltk. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-33231?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Does CVE-2026-33231 have an EU (EUVD) identifier?

Yes. CVE-2026-33231 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-13885.

When was CVE-2026-33231 published?

CVE-2026-33231 was published on 2026-03-20 and last updated on 2026-06-30.

CVE-2026-33231

CVE-2026-33231 is a high-severity vulnerability in Nltk with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-306.

Key facts

Severity: High (CVSS 3.x base score 7.5)
EPSS exploit prediction: 1% (54th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-13885
Weakness: CWE-306
Affected product: Nltk
Published: 2026-03-20
Last modified: 2026-06-30

Description

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.

Frequently asked questions

What is CVE-2026-33231?: 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.
How severe is CVE-2026-33231?: CVE-2026-33231 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2026-33231 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (54th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-33231?: CVE-2026-33231 affects Nltk. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-33231?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2026-33231 have an EU (EUVD) identifier?: Yes. CVE-2026-33231 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-13885.
When was CVE-2026-33231 published?: CVE-2026-33231 was published on 2026-03-20 and last updated on 2026-06-30.

References

Affected products (1)

cpe:2.3:a:nltk:nltk:*:*:*:*:*:*:*:*

More vulnerabilities in Nltk

CVE-2026-0848 — Critical (CVSS 10.0): NLTK versions <=3.9.2 are vulnerable to arbitrary code execution due to improper input validation in the…
CVE-2025-14009 — High (CVSS 8.8): A critical vulnerability exists in the NLTK downloader component of nltk/nltk, affecting all versions. The _unzip_iter…
CVE-2026-33236 — High (CVSS 8.1): NLTK (Natural Language Toolkit) is a suite of open source Python modules, data sets, and tutorials supporting research…
CVE-2026-12243 — High (CVSS 7.5): NLTK version 3.9.4 is vulnerable to a path traversal attack due to an incomplete fix for GitHub Issue #3504. The…
CVE-2026-54293 — High (CVSS 7.5): NLTK (Natural Language Toolkit) is a suite of open source Python modules, data sets, and tutorials supporting research…
CVE-2026-0846 — High (CVSS 7.5): A vulnerability in the `filestring()` function of the `nltk.util` module in nltk version 3.9.2 allows arbitrary file…

All CVEs affecting Nltk →

Other CWE-306 (Missing Authentication for Critical Function) vulnerabilities

CVE-2026-54309 — Critical (CVSS 10.0): n8n is an open source workflow automation platform. Prior to 2.25.7 and 2.26.2, when @n8n/mcp-browser is run in HTTP…
CVE-2026-50242 — Critical (CVSS 10.0): In JetBrains Hub before 2026.1.13757, 2025.3.148033, 2025.2.148048, 2025.1.148120, 2024.3.148430, 2024.2.148429…
CVE-2026-49257 — Critical (CVSS 10.0): mcp-pinot is a Python-based Model Context Protocol (MCP) server for interacting with Apache Pinot. In versions 3.0.1…
CVE-2026-46846 — Critical (CVSS 10.0): Vulnerability in the Oracle WebCenter Portal product of Oracle Fusion Middleware (component: Security Framework).…
CVE-2026-46803 — Critical (CVSS 10.0): Vulnerability in the Oracle WebCenter Portal product of Oracle Fusion Middleware (component: Security Framework).…
CVE-2026-46800 — Critical (CVSS 10.0): Vulnerability in the Oracle WebCenter Sites product of Oracle Fusion Middleware (component: WebCenter Sites).…

Browse all CWE-306 (Missing Authentication for Critical Function) vulnerabilities →