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CVE-2021-43854

7.5 · HIGH

NLTK (Natural Language Toolkit) is a suite of open source Python modules, data sets, and tutorials supporting research and development in Natural Language Processing.

Published Dec 23, 2021CWE-400EPSS 2.60%

Overview

CVE-2021-43854 is a high-severity vulnerability. It was published on December 23, 2021 and has a CVSS 3.1 base score of 7.5 (HIGH).

This vulnerability has a CVSS 3.1 base score of 7.5, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical 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. Versions prior to 3.6.5 are vulnerable to regular expression denial of service (ReDoS) attacks. The vulnerability is present in PunktSentenceTokenizer, sent_tokenize and word_tokenize. Any users of this class, or these two functions, are vulnerable to the ReDoS attack. In short, a specifically crafted long input to any of these vulnerable functions will cause them to take a significant amount of execution time. If your program relies on any of the vulnerable functions for tokenizing unpredictable user input, then we would strongly recommend upgrading to a version of NLTK without the vulnerability. For users unable to upgrade the execution time can be bounded by limiting the maximum length of an input to any of the vulnerable functions. Our recommendation is to implement such a limit.

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

GitHubgithub.com/nltk/nltk/commit/1405aad979c6b8080dbbc8e0858f89b2e3690341GitHubgithub.com/nltk/nltk/issues/2866GitHubgithub.com/nltk/nltk/pull/2869GitHubgithub.com/nltk/nltk/security/advisories/GHSA-f8m6-h2c7-8h9xGitHubgithub.com/nltk/nltk/commit/1405aad979c6b8080dbbc8e0858f89b2e3690341GitHubgithub.com/nltk/nltk/issues/2866GitHubgithub.com/nltk/nltk/pull/2869GitHubgithub.com/nltk/nltk/security/advisories/GHSA-f8m6-h2c7-8h9x

How CyberStrike helps

Frequently asked questions

What is CVE-2021-43854?

CVE-2021-43854 is a high-severity vulnerability. It was published on December 23, 2021 and has a CVSS 3.1 base score of 7.5 (HIGH).

How severe is CVE-2021-43854?

This vulnerability has a CVSS 3.1 base score of 7.5, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2021-43854?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2021-43854?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2021-43854 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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