CVE-2026-33230
Received Received - Intake
Reflected XSS in NLTK WordNet App Allows Script Execution

Publication date: 2026-03-20

Last updated on: 2026-03-23

Assigner: GitHub, Inc.

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` contains a reflected cross-site scripting issue in the `lookup_...` route. A crafted `lookup_<payload>` URL can inject arbitrary HTML/JavaScript into the response page because attacker-controlled `word` data is reflected into HTML without escaping. This impacts users running the local WordNet Browser server and can lead to script execution in the browser origin of that application. Commit 1c3f799607eeb088cab2491dcf806ae83c29ad8f fixes the issue.
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Meta Information
Published
2026-03-20
Last Modified
2026-03-23
Generated
2026-06-16
AI Q&A
2026-03-21
EPSS Evaluated
2026-06-15
NVD
CVE-2026-33230
Affected Vendors & Products
Showing 1 associated CPE
Vendor Product Version / Range
nltk nltk to 3.9.3 (inc)
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Exploitability
CWE
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KEV
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CWE ID Description
CWE-79 The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.
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Executive Summary

This vulnerability exists in the Natural Language Toolkit (NLTK) versions 3.9.3 and prior, specifically in the WordNet Browser application component. It is a reflected cross-site scripting (XSS) issue in the lookup route, where an attacker can craft a URL containing malicious HTML or JavaScript payloads. Because the application reflects user-controlled input into the HTML response without proper escaping, the malicious code can be executed in the browser of anyone accessing that URL.

Impact Analysis

This vulnerability can lead to the execution of arbitrary scripts in the context of the WordNet Browser application running locally. An attacker could exploit this to perform actions such as stealing sensitive information, hijacking user sessions, or performing unauthorized actions within the application. The impact is limited to users running the local WordNet Browser server, but it poses a risk of client-side script execution.

Compliance Impact

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Detection Guidance

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Mitigation Strategies

To mitigate this vulnerability, update NLTK to a version later than 3.9.3 where the issue has been fixed (commit 1c3f799607eeb088cab2491dcf806ae83c29ad8f). Avoid running the local WordNet Browser server until the update is applied to prevent reflected cross-site scripting attacks.

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